The most powerful piston engine in the world

Big is good, it’s official.
As you hopefully know, power is generated in our car engines by burning fuel. The heat makes the pressure go up which pushes the piston down just like you foot bearing down on a bicycle pedal. It’s a nice simple theory. The trouble is that most of the heat released into the cylinder is wasted, at full throttle about a third goes into the coolant and the other third goes down the exhaust pipe. At part throttle its even worse, up to 90% of the heat is wasted. A small fraction of the exhaust energy can be recovered with a turbo but basically it’s very wasteful.
So how can we improve things? Well, to retain more of the heat energy in the exhaust we can reduce engine speed, allowing longer for the heat to be used. But how can we reduce the heat absorbed by the cylinder wall? We could use some funky materials like ceramic but that has its own problems.

An engine, look carefully in the middle there is a bloke on the third floor! (Picture - WÄRTSILÄ)

However, one fundamental scaling rule applies to all things in the universe, if you double the volume of something, the surface area only increases by about 1.4. This is good for engines because a smaller proportion of the heat is lost to the cylinder walls. It’s not so good for creatures that breathe through their skin, like spiders which can never get much bigger than your hand without collapsing in a heap.
So why not use massive engines everywhere? Of course the efficiency bonus of big engines only applies at high loads, at part throttle the massive cooling effect of a high surface area ruins the fuel economy, so in the car world we size an engine to be appropriate for the job the car is supposed to do. For instance, when cruising down the motorway most cars only need about 18 bhp, so building a small engine that has peak efficiency at that power would be great for that single job, and indeed that is what the ‘mileage marathon’ cars do, but of course there is nothing left in reserve for accelerating, so we go for something closer to a 100bhp engine in a smallish car.
But what about something bigger? The biggest vehicles produced are ships, and in particular supertankers which can be the length of a drag race track.
So the subject our adoration is the mighty Wärtsilä-Sulzer RT-flex96-C, in particular the 14 cylinder version. Its total cylinder capacity is 25480 litres, I’ll just let that sink in for a moment.
It is a two stroke diesel engine with four, very large, turbos and computer controlled poppet type exhaust valves. It gobs out 84.4Mw which is 114800 bhp at only 102 rpm, and as you probably know torque is power divided by speed, that equates to about 6 million lb/ft of torque. Which is a lot.
Fuel economy is brilliant at full load – amazingly only 171 grams of fuel per kWh, ok that might not mean too much to most people but it is about twice as good as a diesel car. But if you drop the load to 85% and best efficiency the consumption is only 163g/kWh, which with the fuel containing 42.7 Mj/kg relates to about 51.7% efficiency. But this is not the best efficiency in the piston world, I think that is the Man S80ME-C7, catchy names.
Now that's a big crank, you should see the ballencing machine! (Picture - WÄRTSILÄ)

Everything about it is big in a whole new way; each cylinder is 960mm (37.8 inches) bore by 2500mm (98.4 inches) stroke, giving 1820 litres per pot. At full tilt, 102 rpm that is, a mean piston speed of 8.5 meters per second and the average pressure in the cylinder (MEP) is about 20 times higher than atmospheric which all means that each individual cylinder produces over 7700 bhp (the same as a top fuel drag race car) whilst consuming about 160 grams of heavy smelly fuel oil each stroke.
The outside is even more impressive, they call this type of thing a ‘cathedral engine’. At nearly 14 metres tall, 28 metres long it has four stories of walk ways round it. And weighing in at 2300 tonnes its not going to fit in a car!
Even the fuel pump is impressive, it looks like a huge V8 designed by Dr Frankenstein and delivers up to 1660 gallons per hour of heated fuel oil at 1000 bar to the common rail diesel injection system. Each cylinder has three injectors which are operated independently to control the combustion flow, the way the flame moves around the chamber, resulting in no smoke even at full load. The fuel control allows the engine to run over a wider range of speeds than older generation engines, indeed on the 12 cylinder version they managed to get it to run at only 7 rpm experimentally, that’s one ‘kaboom’ every 9 seconds, which is very slow.
It uses, more or less, the usual two stroke block scavenge intake system, that’s where the underside of the piston compresses the air. But that’s as far as normality goes, here it is refined with one way valves the size of tea trays and then the air hits four very impressive turbos, each the size of a small garden shed, before going through inter-coolers the size of Portacabins and entering the cylinder via a port near its lower edge. For starting, massive electric blowers pump in air at about 30 bar.
The exhaust poppet valves are fully computer controlled, a servo uses oil at 200 bar to move the valve up and down, so the cam profile exists only as software in the virtual world of the control box and is totally variable. The exhaust valve opening is reduced at part load to keep the exhaust temperature above 150 ºC to prevent tons of sulphur from the unrefined fuel corroding the exhaust after treatment system.
The pistons are mounted solidly onto an upper con rod, called a piston rod, that has a joint at the bottom that runs in guide rails, to keep the piston rod upright all the time. It’s called a cross head and ensures that the piston has no side loading and the oil control is tight enough to give the engine a 30 year service life, and most of the time in all those years the engine will be running flat out, which is pretty amazing. The lower end of this rod connects to the con rod proper and then on to the crank, the main bearing caps have ladders on them for the service crew to walk up.
Did I mention it’s quite big?
These engines are used in container ships like the Emma Maersk, about 170 thousand tons of it which is propelled at up to 26knots and is assisted by no less than five 8000 bhp Caterpillar engines just for helping with manoeuvring.
It’s got quite a big propeller too.

Ever wondered how to design a land speed record winning vehicle?

On the weekend of 22/23 May 2010 team Runningblade took the World Land Speed Record for lawnmowers. The magnificent machine was driven by Don Wales, grandson of Sir Malcolm Campbell, on the legendary Pendine sands reaching a speed of 87.833 mph and taking the record for the British team.

Pendine sands at 90mph on a mower!

The original idea was the brain child of team chief Steven Vokins, who’s day job is playing with cars at Beaugleigh Motor Museum, and I was thrilled when he asked me to come on board as technical advisor.
Making a genuine lawnmower do that speed is no mean feat, the machine was built by seasoned mower racers at Countax in their spare time, a quite magnificent effort which not only goes damn fast but is also very stable at speed, looks good and even cuts grass!
In fact part of the regulations required us to cut some grass before the speed attempt, so the lawn outside the Pendine Museum of Speed benefited from a quick trim in front of the world’s media. Currently the museum houses Bluebird, Malcolm Campbell’s land speed record car from the ’20s, so it’s fair to say there is a lot of family history there.
Runningblade also raises funds for two heart charities, so please look at the web site and spread the word. The record breaking run was witnessed by the previous record holder Bob Cleveland who has vowed to take the record back to the USA next year, but he also raised over 1000 dollars back home for our charities, now that is a damn good sport.

Designing a land speed record machine is a skill hard leaned by the pioneers of speed, luckily for us we can draw on their incredible tales to reduce the amount of pain we have to endure. The same rules apply no matter what sort of machine is being designed; stability at speed is essential for safety and to allow the pilot to apply full power, secondly you need to balance power and drag so you can reach the target speed in the distance available.

Early concept work with key parts held roughly in place.

Most speed machines gain stability by using a very long wheel base, in fact it’s the ratio of the track width to the wheel base length that influences the twitchiness of the car, or yaw stability if you prefer the technical term. But making a car to narrow makes it easier to roll, so we start by setting the track width then altering the wheelbase to suit.
The width is a big problem though, for speed we need to make the frontal area as small as possible so it pushes a small hole in the air. Air is heavy stuff, each cubic meter (about the amount of air under a coffee table) weighs about 1.1 kg, driving at 100 mph means that the average car (2 square meters of frontal area) is pushing 110kg of air out of the way every single second!
The ease or difficulty with which it manages to move the air is down to the shape of the car, sleek slippery shapes carve through the air but brick shapes shovel the air in front of them in a massive pile of pressure slowing the car horribly.
And here is the first problem; lawnmowers are traditionally shaped like tractors with a brick shaped bonnet. Luckily Countax make a fairly well streamlined bonnet which became the starting point for the whole vehicle. We also leaned the driver back as far as possible, unlike race cars the view forwards is surprisingly unimportant, usually they are looking a long way in front and so they can be sunk deep into the vehicle with their eyes at bonnet height.
In fact getting everything as low as possible is vital, a low centre of gravity helps stability and crucially reduces the effect of side winds. One of the great problems with a land speed machine is that the aerodynamics are set for minimal drag which means minimal down force, so at very high speed even a slight side wind can blow the car badly off course.
This means that land speed record cars run with a fairly high weight to hold them down at speed, the complete opposite of nearly every other form of motorsport. It’s not that we add weight, more that we don’t try to minimise it, making the structure very strong and the such like. Where the weight sits is very important though, we try to put the majority of the weight over the front axle so the steering wheels have grip, the worst case is the front going light at speed because then the car can spin and roll or on faster machines could flip over backwards. Loosing grip at the back makes the car twitchy and with rear wheel drive obviously acceleration is lost but generally the car stays on course. Going back to the problem of side winds, as the wind blows on the side of the vehicle the most force is applied in the biggest side area, on a mower this would normally be somewhere at the back of the engine area, the point where the car is pushed is the centre of pressure. setting the centre of gravity in front of the centre of pressure means the car is more stable, that’s one of the reasons why proper land speed record cars have a big tail fin.
Brum brum, beep beep...

With all these factors in mind one of the first things we did was to lay all the main components on the floor and get Don to sit on the seat so we could get everything in the right place. Apart from being a useful exercise it is also very funny, and yes we did force him to hold the steering wheel and make brum brum noises.
So now we had the height, width and length sorted out it was time to resolve the details, the most important one being the tyres. Again we have a dilemma, bigger diameter makes a smoother and more stable ride, a wider tyre reduces ground pressure on the soft sand which reduces rolling drag. But the greater the tyre frontal area the greater the aero drag. The decision was constrained by the fact there are no standard lawn mower tyres rated for 100mph, so we had to use ordinary car tyres. Tread pattern is critical on sand, to minimise power lost in breaking up the beach surface we needed the least aggressive tread pattern possible, we even considered slicks at one point, which may seem surprising. But remember we are not doing any cornering, just a straight line, and too much lateral grip could be a problem if it makes the steering too twitchy, if the vehicle does spin it is
Testing, testing and more testing, one day is not long enough.
desirable for it to slide rather than dig in when going sideways to avoid rolling.
Indeed, to stop the steering being too twitchy the rack ratio is reduced making it a lot slower to turn and increasing the turning circle many times.
With all these factors set, we needed to sort out the shape, the aerodynamics and crucially the drag dictates the power required from the engine. At this point well funded teams would model the vehicle on a computer and hone the bodywork in a virtual wind tunnel. We weren’t well funded so we had to do it the old fashioned way, we built a prototype and drove it down and airfield to see how fast it went. Using a data logger lent to us by Racelogic we could see how fast the vehicle accelerated and get accurate top speed readings. As we knew the weight of the vehicle and the engine power curve it was fairly straight forward to work out the drag coefficient.
Who needs a Stig, we've got a Don!

My good friends at Dunsfold Park, home of the Top Gear test track, very kindly let us use the runway for a day. It’s amazing how much work is required before a vehicle can actually drive onto the track, after arriving and unloading the van the initial checks are made and fuel added, I mounted the datalogger and set up the GPS speed reading. Don suited up and the engine was warmed up, that fairly large single cylinder mower engine sounded quite meaty with a race exhaust. A couple of low speed runs warm up the transmission and then it comes back in to check nothing is leaking before the propper test run.
Tring different seat hights and wind deflectors.

The prototype peaked at just over 60mph with a 27bhp engine, which may not sound impressive but it gave us the drag info needed to design the real deal. The prototype had another job to do too; every world land speed record team struggles to find the cash to go on and a vital part of the teams work is generating publicity and generating support, in fact if you saw Runningblade at the launch party at Beaugleigh you saw the prototype, the final version was still being built at that time.
A man with a blue helmet, behind Don is another Bluebird.

One key ingredient is power, in fact more than any other form of motorsport power is critical, and wee needed more. To cover the measured mile at the target speed the vehicle needs more power than you might think, first of all it needs enough power to maintain top speed as it overcomes drag and mechanical losses, but it also needs extra power to accelerate the vehicle comfortably in the run up zone. Not only this but the engine will be running flat out for a long time, so it needs to be able to generate this power reliably but also maintain it as everything runs at maximum speed and temperature, so a degree of safety margin is required and it is common to use an engine with at least 10% more power available than you need.
The problem on this project was the need to use a real lawnmower engine, these usually have the cylinder flat and the crank vertical to drive the front belt pulley. There are not many high power versions about. The 27bhp engine in the prototype was one of the biggest available, but this only gave us half our hoped for top speed, the trouble is the force due to air drag on the front goes up with the square of speed, and worse the power needed goes up with the cube of speed. So to double the top speed we need eight times as much power!
The bigest vertical crank mower motor we could find.

To meet the challenge we needed to drastically reduce the drag as well as increase the engine power. Kawasaki had just launched a new big mower engine and being fabulously helpful lent us one of the first in the country. This mighty 1000cc V twin engine produced well over 40bhp as standard and with a few tweaks we eventually got about double the power of the prototype.
To get the drag down the final version of Runningblade was slightly lower and narrower, the seat canted back a touch and the wheelbase extended to cope.
By now all funds and time had been exhausted, we had booked Pendine sands and the worlds media were pouring in, it was now time to prove we could do it even though we had no time for any final testing.
The view ahead. You need to double click and see this bigger to get it.

Pendine is a fantastically evocative place, there has been so much triumph and tragedy here and Don’s family ties are so great that the land speed museum there houses many of his ancestor’s artefacts. Tides dictate the days timing, as the water goes out it takes time for the moisture in the sand to ebb away, if you drive on it too soon it is too wet and the car will bog down, leave it too late in it is dust and the car digs in, there is a fairly brief window of opportunity of about an hour where the sand is firm and speeds are highest. As soon as the tide has gone the first job is to clear away all the debris by hand to prevent ‘foreign object damage’ or FOD, clearing the drift wood, shells and rubbish is known as fodding and a sterling band of volunteers form the local scouts assisted in this back breaking work. At the same time the course is laid out with the start and finish ‘gates’ being marked out and the electronic timing gear set up and tested. A FIA sanctioned timing official was hired for the day so we could give Guinness World Records verifiable data. Much of the setting up and moving kit about on the beach was done by the local Discovery Owners Club who’s help was vital, they also posted cars at set points on the course to act as emergency aid just in case.
Whilst all this was going on the mower was equipped with it’s cutting deck and a witnessed mow of the museum lawn took place in front of the officials and media, plus a fairly large gathering crowd. No pressure then.
Gina Campbell putting 'Mr Woppit' on Runningblade. Google them. Now!

Then the call came through that the course was ready and the tide time was spot on for the first run, so the cutting deck was removed for safety and we headed for the golden beach.
Initially we ran with a roll cage and harness as we had no idea how stable the mower would be at higher speeds, Don set off for the first timed run, the V twin sounded awesome with no silencing, a bit like a Harley. It soon got up to 80mph and was humming along brilliantly, but then disaster struck and the speed dropped dramatically. We all dived into support trucks and rushed to the scene, the Countax guys flipped the machine onto its tail stand and immediately we could see the drive belt has fragmented. The prolonged run at full power had made it so hot it just disintegrated. Adjustment were made to pulleys to minimise slip and flex and a new belt fitted.
On its tail stand you can see the pulleys that drive the axle and cutting deck.

The return run went without a hitch, Don got out and reported it felt incredibly stable at speed and the beach was at its best, so we decided to remove the roll cage to reduce drag.
The second run was faster, but still not near the target so more tweaks were tried, gradually run by run the speed crept up a tiny amount at a time. There was a gentle breeze up the beach and with a tail wind the machine broke 90mph, but the return run into the wind dropped the average to 86.7mph.
Sun, sand and sea air. How relaxing, oh hang on...

And that was enough to snatch the World Land Speed Record for lawnmowers, the mower had given everything it had to give and it was time to celebrate.

Speed records are strangely addictive, once you have had one you need another, it doesn’t matter how fast you go you want to go faster. Speed is a drug, and the competition at every level is fierce, there is a category for almost everything, even road legal furniture, you name it some one has driven it faster than you would think possible.
Just being part of a team is a real privilege and a thrill, if you love speed machines then why not get involved, I joined the Bloodhound SSC club who have loads of thing for members to join in with and it’s a real buzz. Go on, get involved!

See more about our mower at:

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Twin Turbo W12 vs Supercharged V8 vs 1.6 diesel estate, oh yeah!

Slightly odd Supersport group test

Both Super and Sporty

The ‘Supersport(s)’ label is shared between two of the worlds most powerful luxury cars, both Bentley and Jaguar field ultra fast chariots with force fed V engines. But whilst the Bentley is a stripped down version of its much acclaimed two seat Grand Tourer, the Jaguar is a full fat version of its four seater limo. Two very different markets, two very different cars, but one very good excuse to go thrashing fast cars round the fabulous Millbrook test tracks. Oh I’ve gone all misty eyed just thinking about it. But this is no ordinary ‘journo thrashes a fast car’ type article, oh no, there is an angle that may enlighten…
The Bentley Supersports

Just walking up to the truly magnificent Bentley Continental GT Supersports is an occasion. As I get closer details start revealing themselves, there are no less than four radiator grilles plus two elongated bonnet vents which all collude to give the impression of a barely contained massive powerhouse under the hood. The huge alloy wheels, polished to within an inch of their lives, do nothing to conceal the equally huge cross drilled brake discs and shiny black callipers with Bentley scripted in elegant white lettering. Everything about it spells power, pure and simple.
Bore quilt than a blanket factory

Inside is furnished with the obligatory herd of dead cows but with the addition of box quilted fabric inserts in the door cards and seat centres, this combined with the beautifully crafted and very usable knobs and leavers with polished and machined metals gives a feeling of a classic luxury aircraft. Maybe I should have worn a flying jacket for this one.
A knob, possibly the best knob, but still a knob.

Firing up the mighty W12 twin turbo engine is disappointingly undramatic, it just starts immediately and settles into a refined hum, surely this sort of machine should burst into life and crackle into a snarling and lumpy idle? OK, maybe that’s just me then. Being primarily a luxury car refinement is still prominent, but as the sporting variant the exhaust has been allowed a bit more freedom, the suspension is a touch firmer, its just over 100kg lighter and generally the driver feels more connected to the road. Which is nice.
Obviously with 630PS on tap from the 6 litre twin turbo W12 performance is brisk, in fact the 0-60 dash takes 3.7 seconds according to the spec sheet, but its delivered in a refined and constant wave of thrust as 800Nm of torque sweeps from a mere 1700rpm up to 5600rpm in an artificially constant level. This smoothness can be a bit deceptive, with the speed flooding in almost unnoticed. The stability control works with the 4×4 drive system delivering 60% of the thrust to the rear and allowing a tantalising amount of over steer drift when powering out of corners.
As an experiment I set it up for a long sweeping corner with a little over steer, then floored the accelerator pedal (can’t call it a throttle pedal any more as it
Arguably another knob.
isn’t directly connected to the throttles) to see what happens. Doing this in a 600bhp car a few years ago would have resulted in instant death as the back wheels spin into oblivion and the car pirouettes into the scenery, no such drama with modern cars as the stability control adjusts engine power as well as brake balance (yes it applies the brakes when you accelerate in a corner) left and right to keep the car pointing in what it thinks is the desired direction. All very clever, and essential if you are going to let ordinary members of the public loose in cars with twice the power of an original Countach! That’s why pretty much every modern car has some form of stability control, as an example going back a few years the Sierra Cosworth had a reputation of being a bit to powerful and wild, but that only had 204bhp which is less than an Audi diesel estate. How times have changed. Anyway, back to the Bentley which is still balanced on the power round that long corner…
When pushing hard the body roll is noticeable but controlled, you can feel the weight but it feels much less than the 2240kg that this ‘lightweight’ version of the Continental has. But it’s on the straights that the flying B excels, even on the damp Millbrook test track it rockets forward with unrelenting pace, luckily the massive ceramic brakes haul the speed down with even greater force, a testament to the amazing capabilities of the Pirelli 275/35ZR20 tyres. Interestingly the rear track width has been widened by two inches to improve handling, I say interesting because this now makes both the front and rear track near identical to the standard Jaguar XJ, strangely I never thought of the standard Continental GT as being a narrow car…
The last part of the stunning Millbrook ‘Alpine’ route, which I am sure used to be simply called the ‘Hill’ route before it featured in a James Bond film, is a little jump simulating a hump backed bridge. Actually it is not supposed to be a jump, drivers are supposed to slow down, but as the multitude of sump scars in the tarmac attest temptation to play can be irresistible. Anyway, the Bentley landed with minimal damage and carried on its way, ahem.
As I departed that circuit and drove gently back to the base camp situated in the middle of the complex of tracks and circuits the refined aspect of the car showed through, wafting me through roundabouts and junctions, pulling away on wet concrete T junctions with absolutely no drama, all in all a very usable and impressive car
Suportive seats, responsive controls and epic power = my Bentley of choice.
indeed. In another decade it would have been called a supercar, but in this moment it is just a blindingly fast big GT with epic presence.
Jaguar XJ Supersport

Stepping from the glitz of the Bentley, the stylish Jaguar feels almost minimalist with that wonderful thin sweeping arc of dark wood traversing the dash and door tops, and just two air vents to break up the lines, with the digital dash sunk deep into the binnacle.
Stylish interior, not sure I would choose grey though...

But here’s the thing; it is because I was just in the Bentley that the Jag looks Spartan, if I had just been driving a ‘normal’ car would it feel as empty?
And this is a crucial point, everything is relative, particularly in something as subjective as a road test. It’s all about reference points, it’s all very well for a motoring hack like me to go swanning around in super-fast luxo cars all day and say one has slightly better on the limit handling, but this is meaningless to anyone who doesn’t drive these cars on private test tracks.
So for this group test I brought in a bit of a wild card, possibly a joker, but in any case a dose of normality. The third car in this group test is the very capable Skoda Superb, the estate version, with a 1.6 diesel.
This is what normality looks like.

Now at this point you might think I have lost the plot, and obviously you might have a good point, but bare with me and hopefully things will start to make sense. No guarantees though.
A foot longer than the Bentley, but more elegant somehow.

Back to the Jaguar XJ Supersport, a totally different type of car to the Bentley with a full set of luxo seats and four zone climate control. The ‘sports’ aspect comes from the optional active differential and the supercharged 5.0 V8 engine. Pressing the start button breathes life into the surprisingly ecological recycled aluminium block, indeed it is amongst the smallest of the big engines (such as the Mercedes 6.3, the above mentioned Bentley 6.0 etc.) but punches well above its weight. Again this is a trend we will see more and more of, where manufacturers use smaller engines with more boost to deliver even higher performance levels than their older big engines, the VW Tsi uses a 1.4 to give 170bhp as an example.
Refinement is a Jaguar speciality and the car effortlessly glides away, as the speed rises the only thing that spoils the ride is the low profile tyres, a problem that infects far too many cars these days.
But the Mr Nice-guy pretence is dropped as soon as the big Jag hits the test track, flooring the loud pedal engages warp drive which turns the swooping hill roads into a high speed roller coaster and the engine note is transformed into a gruff roar by the exhaust muffler bypass valves and a very cunning device that brings a subtle sample of the superb intake noise into the cabin.
In gear acceleration on a real road feels very similar to the Bentley, the 6 speed gearbox has very swift and precise shifts (both cars use the same ZF 6 speed box) but going fast into corners the Jag seems to carry more speed with less roll and greater composure. This is not surprising when you consider that this short wheel base XJ (still a foot longer than the Bentley) weighs in at 1892Kg, that’s over 300kg less than the Bentley despite being bigger with more seats and toys.
There are two reasons for this massive weight difference, first is Jaguar’s use of an aluminium shell, a technology they first used with on the old XJ and refined on the XK. Many manufacturers have looked at ally shells and of course Audi use them on some cars, but production challenges make it a much more expensive process and requires a lot of specialist knowledge to get right. On premium cars manufacturers can sometimes pass on the extra cost, but for mid range cars it is still not commercially viable which is probably why Jaguar still use a steel shell for their XF.
But the world is changing, and now fuel consumption (and therefore CO2 emission) is under scrutiny. This may tip the balance in favour of ally shells, just look at the CO2 figures for the Bentley (388g/km) and the Jaguar (289g/km), that’s a huge difference. As laws come in that will set ever tightening limits on CO2 even supercar manufacturers will have to take action.
The second reason for the weight difference is because the Bentley has four wheel drive, so has an extra transfer box, front prop shaft, front diff and half shafts. You might be thinking that this is unnecessary baggage for a GT car, but consider this: much of Canada, Russia, Scandinavia and the new markets in China spend a fair chunk of the year covered in snow where a rear wheel drive car will struggle to get off the drive way, they also have a lot of new rich who want a car they can be seen out in, you do the maths. Right, back to the track.
It’s remarkable how similar two very different cars can feel when being thrashed round a track, both have more than enough grunt to power up the very steep twisty hills of Millbrook and fling the occupants over the crest at break neck speed. But pulling away at that damp concrete T junction in the Jag highlights the big advantage the Bentley has with its 4WD, the rear wheel drive Jaguar limits wheel spin as it maximises grip from just two wheels, and whilst there is no drama pulling away there is also less acceleration. I suspect this is why there is such a big difference in the 0-60 times with Bentley smashing it in 3.7 seconds and the Jaguar smartly stepping forward in 4.7.
Both these cars are quick, in slightly different ways, but how quick are they in real terms? And for that matter how quick is quick anyway? To find out I drove exactly the same route in the Skoda estate diesel. The first thing I notice is the noise, the estate is very good for noise in its class, but having just complained about road noise from the Supersports low profile tyres I take it all back compared to the road noise at motorway speeds from a normal car.
As I head onto the first section of track I accelerate, but nothing happens. Two things are worth noting, firstly in all three cars I started this bit at about 70mph, in a normal car flooring the accelerator at 70 will obviously result in only mild acceleration, but when you have become accustomed to the Bentley or Jaguar you automatically expect neck snapping acceleration at this speed. Secondly this section of road is up hill, in the other two cars I hadn’t even noticed it was up hill, in the normal car I am considering changing down just to keep the speed up.
After a few tight corners to get the tyres up to temperature I hit the long left hander, in the other two cars I went in slow, about 60mph, and powered out to asses how they handled hard acceleration in corners. In the normal car I struggled to get it round at all at 60mph, let alone accelerate. It was in fact a fairly tight corner, but the big cars just grabbed hold and got on with it in a way that a normal car could never do.
A very good car made a useful referance point.

Through the twisty bits I had noticed the Bentley had a bit of body roll, at a lower speed in the normal car changing direction mid corner resulted in a lurch rather than roll and enough tilt to worry about scraping the mirrors in the road, turns out that ‘bit of body roll’ was actually blooming impressive at that speed, and the fact that the Jag had even less turns out to be stunning. Again, totally different worlds.
Then there is the ability to be pushed hard all day, the hill route is relatively short, just a few miles, so the big cars had barely warmed up by the time it was over. By contrast the normal car was loosing power (modern diesels wind the power down when the intercooler or oil gets hot to preserve longevity) and the brakes just started to fade. This is no bad reflection on the car, no one in their right mind would drive a 1.6 diesel estate that hard for any length of time, it’s just silly and on anything other than a private test track it’s suicidal.
I think it’s important to get a sense of perspective, in order to better understand what is being looked at, I learned a lot about the Jaguar and Bentley by driving a Skoda Estate. Skoda also very kindly let me loose in their rather excellent VRS which is undoubtedly a fast car, in a different class of performance to the normal estate car, but again several classes behind the big boys.

All this goes to show the effectiveness of the Bentley and Jaguar suspension, brakes, control system, engine and transmissions. And indeed that of any of the very high performance cars about these days. There is a lot more engineering in one of those, and when I see the price tag the size of a house I can’t help but think that actually that’s not bad value. These cars are not just good, they are amazing.

De-mystifying the Jaguar V12

The Jaguar V12 engine is one of the greatest iconic powerplants ever made, powering the E Type, XJ12 and XJ-S models plus numerous successful race cars from Touring Cars to LeMans GTs. But for some the apparent complexity makes it a very scary option. Having raced these magnificent units I feel it’s time to set the record straight.

Looks simple enough....

The first time I opened the bonnet on my XJ-S V12 I just stared at it in disbelief for a few minuets, then gently shut the bonnet again and walked away. To say it was full would be an understatement, it looked like someone had emptied a very large bucket of automotive spaghetti into the engine bay until it was full, then smoothed it off with a very big oily trowel.
Which is a very great shame, because the engine itself is a fairly straight forward design, just with 12 of everything. Owning and driving one is a fantastic pleasure, round town the engine is silent from within the cabin and it is arguably more refined than a Rolls. On the open road it has a briskness that defies its size, and given enough space has a relentless thrust that just keeps on going.
So if you have a desire to own one then don’t let the tales of woe put you off. It is only that the parts bolted on to the engine, such as the fuel system, air control system and electrics that seem shockingly complex, and that is only until you get the hang of what does what.
The good news is that the engine itself is very reliable and can cope with a huge amount of abuse, the bad news is that because of this many older cars have many missed services, giving the new owner quite a lot to do. The base engine has gone through three main changes over the years; the original E Type and XJ engine had flat cylinder heads and is the one preferred by the racing fraternity, but it had an alarming thirst for fuel. The fuel crisis of the 70’s led to the High Efficiency HE engine, introduced in the early 80’s, with a very high compression ratio and very special combustion chambers with a heavily recessed intake valve for very high swirl rates, this limits tuning potential slightly but gives amazingly reasonable fuel consumption, I used to achieve about 25mpg on a run from my XJ-S HE. The HE stayed in production into the 90’s when it was replaced by the 6 litre bock which was largely the same but with a longer stroke.
All these engines are very robust, as they are derived from the XJ13 race engine the 5.3 revs to 6500rpm and the 6 litre goes to 6000rpm. Because they are designed to be quite happy running at these speeds, in an every day road car they are totally unstressed. Of course this pedigree means it is still great for classic racing today, many racers take engines straight out of scrap cars and merely change the oil before heading for the track.
Speaking of oil, it does take quite a lot of the slippery stuff, over 10 litres is usual making an oil change a substantial investment. The oil tends to last quite well however, an oil cooler is standard and the engine’s quick warm up system minimises oil contamination. When changing the oil it is best done with warm oil, as with most engines, but leave the exhaust for a while to cool down because the oil filter is right next to the down pipes and contact is inevitable.
The simplest incarnation was in the carburettor fed E Type and XJ12 models, but the engine was designed for fuel injection from the start, and as soon as a suitable system was available it was fitted to the XJ12, the XJ-S was injected from the start. The systems was very sophisticated with little extra features to enhance performance and emissions, all stacked on top of the engine, making it look so complicated. Breaking it down a bit, there are six main systems in that spaghetti; fuel, vacuum, engine management, ignition, cooling system and air con.
I will take a typical S3 XJ12 as an example, then go over differences on other models later. Opening the bonnet reveals a network of small bore tubing, some of this is the fuel system with the U shaped fuel rail feeding all 12 injectors, but most of the small tubing is the complex vacuum operated control system for the distributor. The front of the engine is dominated by the air con pump with its cylindrical silencer, yes that’s right the air con pump has a silencer, very refined.
You will also notice it has two cooling system pressure caps, one at the front of the engine and one on the expansion bottle on the wing. Nearer the rear of the engine is the throttle pedastle, this is where the throttle cable operates a circular device that in turn operates the two throttle links, more of that later.
With a gearbox on its over 7 foot long and weighs half a ton
Lets start with a potted history of the ignition system, it has gone through several major changes over the years, most models of the 70’s and 80’s use the 12 cylinder Lucas Opus distributor, similar to many other BL cars of the time. The HE engine’s high compression ratio required much more spark energy at high speed than the older engines, and feeding a spark to 12 cylinders at engine speeds up to 6500rpm require the coil to store a lot of energy, it was too big a job for just one coil back in those days so the cunning chaps at Jaguar doubled up the coils, one coil has the king lead to the dizzy and the other sharing only the low tension 12v side of things. This secondary coil looks a bit odd, as the king lead post is blocked off, the main coil is located next to the dizzy but the secondary coil is mounted right at the front of the car, in front of the radiator, if its faulty or missing then the engine will misfire at high rpm but may well run perfectly round town.
Later models managed to use just one, more modern, coil. But when computerized mapped ignition was installed the need to have the coil towers further apart required a novel system from Mirelli which effectively incorporated two 6 cylinder distributors in one, stacked one on top of the other in the same housing. This system has two coils next to the distributor and two king leads feeding a split level rotor arm.
The final iteration of the V12 ignition saga happened after the change to 6 litres when the distributor was deleted in the and replaced with individual coils for each cylinder.
Of these systems the most common is the Opus, and it is also the one with the most complicated vacuum advance system ever made. Its also very clever. To get the best from an engine the ignition advance must adapt to all engine operating conditions, a simple vacuum advance system is a big compromise but back in the 70’s full computer controlled mapped ignition was not an option for mass production. So the vacuum capsule is connected to several air solenoids, a vacuum regulator, a vacuum dump valve. The biggest problem with this comes from old rubber hoses perishing, the second biggest problem comes from people re-assembling the system incorrectly. One of the clever things the system does is warm the engine up quickly, and its huge amount of coolant. The ignition is retarded when cold and extra air is let in via an air solenoid, this is controlled by its own little electronic box of tricks which has been known to go wrong resulting in lost power and idle problems, but when it works it works very well. To compensate for lost power when running so retarded extra air is let into the manifolds by yet another solenoid. It is possible to remove this system completely, the only down side being longer warm up times.
One of the popular horror stories about this engine is that the spark plugs are impossible to change without a major engine strip down. Well, in fact most of them are no problem at all, but the front two are very close to the air con pump, a special tool is recommended but another option is to undo the pump belt and mountings and ease it over, without damaging the hoses, to get enough access.
Because of this difficulty it is quite common for the plugs to be left in far too long and start to corrode in place, so its worth blowing all the dirt out of the plug recess and allowing some penetrating oil to soak in before attempting removal. In fact it is quite important to blow any detritus out of the way first, the plugs are ate the top of the engine and it is easy for debris to accidentally fall down the hole during the change. Make sure you get the right plugs too, there was a change of design to taper seats when the HE engine came in.
The electrical system design also laughs in the face of convention. The fuel injection control really was cutting edge and in some ways daring. The early, pre-HE, ECU was relatively simple but very good at its job, the HE ECU is more sophisticated and has a manifold pressure sensor built in to the box. Unusually the ECU is mounted in the boot and the wiring for the injectors and sensors passes through the rear bulkhead and takes a tortuous route through the interior and finally emerges through the front bulkhead from whence it sprawls over the engine and wing edges to meet the control relays mounted on top of the radiator. The HE system also has a vacuum hose from the intake manifold going all the way back to the ECU. Obviously there is the potential for older cars wiring or vacuum hose to have expired in some way. Electrical connections are prone to corrosion which can usually be removed reasonably easily, but sometimes it works out easier to fit new connectors. The vacuum hose is worth replacing if its older than a decade.
The throttles, one on each intake manifold for injected engines and four on carb versions, are operated via a centrally mounted disc which is pulled round against a spring by the throttle cable, this disc also operates the load cable for the auto box and the cruse control, it also has a switch on some models for the auto box kick down and the throttle potentiometer for the ECU. So all in all its a complicated part, but all you usually need to do to it is check that the throttles all start to open at the same point, if they are a little out of balance the engine might only be using half its cylinders as you cruse round town, luckily its a simple operation involving undoing the lock nuts and winding the links in or out as described in the service manual.
The fuel system is quite remarkable too; on the XJ-S there is a fuel pump in the boot sitting in its own little tank, fed by gravity from the main tank. On XJ12 there are two main fuel tanks which both feed the fuel pump in the boot but with fuel solenoids to select which tank is used. The excess fuel returns from the engine to the tank, but because the fuel picks up so much heat in the massive engine bay it goes through a small cylindrical fuel cooler that is plumbed into the air con return pipe.
Early systems suffered from hot re-start problems due to having very small bore fuel rails which are prone to fuel vaporisation in the heat, the later larger bore system is a useful upgrade. When the returning fuel gets to the tank it goes into a pipe in the main tank which in turn goes back into the pump tank, that way returning fuel is mainly pumped straight back to the engine and the main fuel tank temperature doesn’t rise too much. This is all done to stop fuel evaporating, which became part of the emissions regulations in the 70’s, instead of the tank just venting to the atmosphere it vents into a can, tucked up into the right hand buttress on XJ-Ss and one on each rear pillar on XJ12s, which allows the vapour to condense and return back to the tank via yet another small bore pipe, determined gases are allowed to escape via a restricted pipe on the top of the canister which goes to the engine intake.
Needless to say its a very complicated system and is prone to problems, one of which is a strong smell of fuel in the cabin. Some owners rip the whole vent system out and replace it with conventional vent pipes.
Later models supplement this vent system with a carbon canister in the engine bay which absorbs fuel vapour and is emptied into the engine intake during part throttle running, ensuring the vapour is burnt and never vented to atmosphere. This is controlled by the engine ECU via a solenoid in the pipe from the canister to the intake.
Although all this pipework looks intimidating initially, all you really need to do is keep the hoses in good order, and if you are so inclined the system can be simplified and most of the plumbing removed.
The cooling system is another stunning work of art. Each cylinder head has an externally mounted coolant manifold with a thermostat and top hose at the end, in the E Type both top hoses go forward to the radiator, which was the traditional sort with a tank at the top and the bottom and the cores running vertically so the two top hoses went straight into the top tank, relatively simple compared to what happened next.
On XJ models it got a lot more complicated, a more modern radiator with horizontal flow and a separate expansion tank is used for greater efficiency and lower bonnet lines, and with a tank ate each side it made connecting the two top hoses a bit more tricky. The solution was to put a baffle plate one third of the way down the left hand tank, effectively splitting the radiator in two. The left top hose goes to the top of the left tank and the coolant then flows across the top third of the radiator into the right hand tank where it is joined by the right hand top hose. Then the mixed coolant from both heads goes back to the lower left hand tank via the lower two thirds of the radiator. Still keeping up? The bottom hose is attached slightly above the bottom of the lower left hand tank, and then feeds back into the water pump.
To make this set up work a small bore hose connects the top of the radiator to the expansion tank, mounted at the side of the engine bay. This tank feeds back to the radiator via a bigger hose at the bottom. It also supports one of the hoses for the interior heater, the other coming from the back of the right hand cylinder head coolant manifold. At the top of the tank is a pressure cap, but because this is not the lowest point in the system it should not be used to check the coolant level.
Amazingly it gets more complicated, between the two thermostat housings is a balancing tube which supports a second pressure cap, it is here that you should check the coolant level.
If you make the mistake of opening both pressure caps then coolant will drain from the top of the engine into the expansion tank and spill out. The highest point in the system is the interior heater matrix, so when refilling the coolant after a change it is best to have the front of the car raised a bit. You wont be able to get all the coolant in in one go, the trick is to run the engine with the heating on full and give it a few revs briefly then switch off and magically you can get the rest in.
Bizarrely the standard service schedule specifies dropping two pots of Barrs leaks with every coolant change, probably due the the huge number of joints in the system. This can lead to clogging in some of the coolant galleries and the interior heater matrix, so a good flushing can be helpful, and as ever old rubber hoses should be renewed every ten years or so.
Although this set up is genuinely complicated, all that is needed is normal maintenance such as coolant changes and checking for leaks, so don’t let it scare you off.
The front of the engine sports four belts on most models, and again although it looks complicated it really isn’t. at the back is the alternator belt, tensioned by moving the alternator, then there air con drive belt which is tensioned by a high mounted idler pulley, next we find the belt that drives the water pump and power steering pump tensioned by moving the PAS pump, lastly there is a fan belt with its own little tensioner pulley.

So there you have it, a glorious engine hidden under a complicated dressing. Although there are many neglected examples around, with some careful attention going through each system a stage at a time will ensure many happy years of sheer motoring joy.

Recall in perspective: What can possibly go wrong….again..

One in a million.

My boss told me “so that means your design will defiantly kill two people per year!”.

That was 20 years ago, when I was a fresh faced engineering graduate in my first job at a global car maker. I was designing bits of engine management system, and as ever I had gone through every type of possible failure and worked out how well it was catered for. But one very obscure scenario involved the car stalling on a hypothetical level crossing near a strong radio transmitter, a bit tenuous but it is a situation that could happen, I had gone through the figures and worked out that it was a million to one chance that the engine would not restart, resulting in something bad involving a train and sudden localised distortion to the car (ok, a crash).

Danger being recognized

I thought that this was a remote chance, but my then boss pointed out that the systems would be put on about 2 million cars per year in Europe, hence his terminal conclusion.

I redesigned it. No one had to die.

But even so, I am sure there could be even more obscure situations I had never even thought of, I probably could have spent years going through more and more complex scenarios, but the the car would never have been made. So we have to draw the line somewhere.

How common are uncommon faults?

So its with a great deal of sympathy that I read about Toyota’s sticky pedal problem, millions of cars work fine, yet a handful of freaks necessitate a total recall. You just cant take chances, even if most of the cars are absolutely fine.

Toyota are no worse than Ford, Mercedes and all the rest, all volume products suffer from occasional problems, largely due to the scale of production and of course because we want them cheap, and that’s not going to change any time soon.

When an industry has to make very complicated machines, that are used by the general public, and have to endure a vast array of harsh environments, things are going to be difficult. And when this problem is massively compounded by having to make the car as cheap as possible, something has to give.

Times this set of problems by the millions of cars made every year and the law of averages is definitely not on the side of car makers.

If you think about it, the mere fact that when something does go wrong it makes the headlines tells us something about the utterly fantastic job that all these companies usually do.

If the average Joe knew anything of the vast amount of sheer hard work that goes into creating cheap, economical, useful and reliable cars they would bow down in reverence, and those that fancy their chances at suing for spurious accidents would hang their head in shame.

But hardly anyone knows about all that fantastic engineering work, it doesn’t make sexy TV programs, it’s not vacuous and glamorous enough to make it into the glossies. So every one just accepts that every machine should work perfectly no matter what, and are utterly surprised on the very rare occasion that it doesn’t.

Cars are amazing.

Here’s a challenge for you; think of a machine that has to work in heavy rain, baking sun, snow, ice, deserts, tarmac, cobble stones, at temperatures between -40 to +50 C, last over a decade whilst being shaken, accelerated, decelerated by novice users in a crowded and complex environment.

There are no other machines, just motor vehicles, which have to contend with all this.

But it doesn’t stop there, the engine is retuned every combustion cycle, hundreds of times each second. The suspension analyses the road and adapts to suit, the auto gearbox monitors the drivers ‘style’ and changes the way it works to please them. The brakes check wheel speed thousands of times a second and deduce when a tyre is about to skid and relieve brake pressure just before it happens.

Components have to operate faultlessly for millions of cycles, if an engine or drive-line fault develops then the systems must identify it, adjust the mode of operation to minimise risk and alert the driver, just like having an expert mechanic on board.

In addition the car has to be comfy, economical, perform well, have a really good sound system and be near silent in operation.

Not even the Space Shuttle has to contend with this level of sophistication.

And here is the kicker; as well as coping with all that, it also has to perform special functions in a crash. We have multiple air bags, who’s operation is tuned to the ‘type’ of crash detected, we have automatic engine cut, hazard indication, seatbelt pre-tensioning and some cars even ring for help.

Name me one other machine that has to detect, reliably, when it is about to be destroyed and then deploy safety mechanisms during the actual process of destruction. You’ll struggle with that one.

Now this feat of engineering would be amazing even with an unlimited budget, but the fact is that cars are made as cheaply as possible, which just take the achievement from amazing to utterly astonishing.

Please take a few moments to look at your own car, and marvel. And if one part goes wrong, be sympathetic to the scale of the problem engineers face.

Media hype

During this recall, the media could have played a very useful role and helped society, I say ‘could have’ because what they actually did was the complete opposite.

What they could have done is reported actual news, facts presented objectively such as ‘a small numbers of cars may have a fault causing the pedal to be stiff’. That is a fact, it gets the info over simply and effectively, you know what is being said. Simple.

They could have gone further and said something like ‘if your pedal feels stiff visit your dealer, but first check the floor mat hasn’t got stuck under the pedal’. That would be helpful.

But they didn’t do that.

No, what actually got reported was ‘mum of five in death plunge tragedy’ and ‘is your car a ticking time bomb of doom?’. Stupid, dramatised gossip that conveys absolutely no useful information.

But of course this scare mongering helps to boost sales of the current media bilge, so expect more useless crap in the future about every important storey.

And this is a real problem, not only because it leaves us all badly informed and scared, but because the car companies now know that being honest and open has become the wrong thing to do.

All media has a responsibility, and its time they faced up to it.

People are getting to be useless.

And this brings me to a very important point; cars are so reliable these days that people are totally unable to cope with a simple problem; I would have thought that if the pedal stays down then either put your toe under it and pull it up or drop it in neutral, park up and switch off. Easy, but most people have lost the ability to cope with any sort of problem, and that is scary.

I say scary because we depend more an more on technology, cars, electricity supply, computers, the internet, mobile phones, the list goes on. And for the most part the technology serves us amazingly well, but like all things it can fail.

I remember in the 70’s there were power cuts, no problem; the lights went out so we lit candles, life goes on. We communicated by actually talking to people, we were entertained by actually doing things, we worked by going out and making physical things.

But now, oh dear, if the power fails we seem to be doomed to sitting in a freezing dark house unable to phone a friend or do any work on the computer. ‘Doomed I say, doomed, captain’ (although that phrase probably wont mean a thing to younger readers).

Now don’t get me wrong, I am a great fan of technology. As an engineer I work on car technology that won’t see the glowing lights of a showroom for maybe seven years, as a writer I would be lost without the word processor and its fantastic ability to correct my abysmal spelling. Oh yes ineedy I just cant get enough of the techy stuff.

What I am scared of is the way people are loosing the ability to do things for themselves. To even bother trying to solve problems seems to great a challenge, the mind is being numbed and switched off, its like intentionally loosing the ability to walk just because you can afford a wheel chair.

The first though now seems to be ‘who should I call about this problem’, and not what it should be ‘what can I do to solve this problem’.

People have to be more proactive, just like we used to be, and much less reactive and just plain pathetic.

Mind you, I suppose if there were to be a mass technology failure and every useless person was, well, useless, then maybe Engineers will rise as a united force like a waking giant and take over the world. So its not all bad. 😉

Technology marches on.

Here is an interesting observation: most drivers don’t want to be there.

Unlike enthusiasts, such as myself, who really get a deep enjoyment and fulfilment from driving, in the mass market most car owners don’t actually like driving at all, it’s just become a necessity of modern life. That’s why so many of them don’t pay attention and would rather chat on the phone, listen to the radio or just stare into the distance like a slack jawed zombie.

Cars are a very strange phenomenon in that respect, where else would you find a large, heavy and complex piece of machinery operated by anyone who wants one? It wouldn’t happen with lathes, welding kit or submarines, but with cars we just accept it.

And because of the non-professional nature of the vast majority of car owners, technology is being developed to meet their needs. That is; making the car make most of the decisions.

We are already seeing Volvos with ‘collision avoidance’ brakes which do an emergency stop before you drive up the arse of the car in front. Many cars have adaptive cruise control using radar sensors to move with the flow of traffic, some cars have lane assistance which nudge the steering to keep the car between the two white lines. And fully autonomous cars are in development, you just get in, tell it where to go and it drives you there.

To many this is automotive heaven, just like having a chauffeur, and takes the irritating burden of ‘having to do some driving’ out of a journey completely. Plus there are safety advantages which make a very compelling argument, the fact is that nearly all accidents are caused by the driver doing something really dumb, so by taking the driver out of the system lives would be saved. And that argument alone is powerful enough to kill the ‘drivers car’ stone dead, no arguments, it is simply infeasible to argue that autonomous cars should not be compulsory just because we want to have a little bit of fun.

But to enthusiasts this is automotive hell, no control, no involvement, no enjoyment, nothing.

And it also take a lot of skill and judgement away too, what if I want to drive on the left of my lane to get a good view past the truck I am about to overtake? Will the lane control system let me? What if I need to gently nudge my driveway gate open because its blown shut? Will the collision avoidance system let me?

But what drives technological development is consumer demand, so if we want cars to be ‘drivers cars’, totally under our command, then we have to make our voice heard. Not only that but the voice must have a strong and sound argument, and it has to be heard right now.


What’s the greatest challenge facing car design? Meeting carbon emissions targets is a damn good one, as is crash safety. But by far the biggest problem facing car design is complexity, and its a problem that is being hidden.

With all the highly sophisticated systems on board, such as engine control, ABS, crash avoidance, gearbox tuning and even sat-nav, knowing exactly how each part will react to the behaviour of another part has been almost impossible.

But modern cars don’t just have a set of independent systems, they are linked together. This has provided some amazing cross-function capability, such as traction control where wheel slip is detected by the ABS system and the engine system reduced power to suit, and it has given us seamless automatic gear shifts where the gearbox talks to the engine to ensure the speed and power are matched perfectly as a gear is changed.

More importantly it has enabled much greater safety, for example if the brakes fail then the electronic hand brake system can lend a hand and the engine and gearbox can work together to increase engine braking.

It can even compensate for driver incompetence; some people panic in an emergency and press both pedals to the floor, modern cars detect this and simple apply the brakes and return the engine to idle. This simple step has saved lives.

Now, the concepts of integrated safety and functionality are simple to understand, the arguments for and against them are again fairly simple. Even politicians can understand them.

But the devil is in the detail, and when you get down to the actual computer code it gets mind bogglingly complicated.

I will give you a relatively simple example. In order to reliably detect if the accelerator pedal sensor has failed, the pedal has at least two independent circuits, the signals are compared to see if they agree, that way if a wire is broken then the system will detect it and the engine can be safely returned to idle. But it has to do more; what if there is a mechanical failure such as a broken return spring? Well, the signal is also analysed for movement so that if it stays inexactly the same position for too long then there is a fair chance its stuck. But how long is ‘too long’?

This is where it gets tricky. The signal is also compared to other signals, such as the brake pedal as mentioned above. But even if both brake and accelerator are applied at the same time, what if the fault is not in the accelerator pedal, nor in the driver panicking, but in the brake pedal sensor? This could lead to a tragic loss of power when the driver needs to accelerate out of danger, such as on a railway crossing.

So one layer of complexity involves where do you set the limits, how much analysis do you do and how many other systems do you compare with?

But there is more complexity, oh yes, much more. What if the various systems are not entirely in tune with each other? For instance when braking, as the speed drops the gearbox changes down and requests the engine speed to rise to match, so the throttle is opened. Usually the various signals are perfectly matched and this works seamlessly, but what if the signal from the gearbox results in a momentary surge of power from the engine?

So clearly the teams developing and tuning the brakes, gearbox and engine have to work together to ensure that under every different level of braking and speed combination, everything matches up. And that is a lot of work.

However, it gets more complicated. Many companies buy in certain systems, maybe the ABS from Bosch, the gearbox from GM, possibly even the engine might come from another company, or another division in a different country. And even within those teams, parts of the computer control code may be outsourced to other divisions or companies, bringing another layer of remoteness to the design.

See where this is leading? Well, to greater complexity and less understanding of what every part has in it.

That is just one example of one system interaction, but there are many more, and each system may have further unintended interaction too. A classic on is with ‘stability control’ systems, when accelerating out of a corner a driven wheel might start to loose traction, so the traction control system will apply the brake calliper on that wheel to keep it under control. This causes the car to veer off course slightly so the stability control applies the brake calliper on the other side to balance it out. Net result is you end up accelerating with the brakes on!

Now modern cars are introducing collision avoidance, lane control and other complex systems which all have to work in harmony with all the other systems in all the infinite combinations of circumstance.

I believe that it is now impossible to accurately asses how such a car will react in all conditions.

This is true not only for cars, but in many of the systems we rely on today, from automatic number plate recognition and speeding fines, military automatic targeting and smart weapons, to the DNA database and even the way we use the internet.

The potential for technology to assist is immense, but it has to be understood that we have now lost control of every detail. So how far do we let the machines dictate to us, and how much override can we allow to fallible humans?

The answer to this will dictate the future of society and quite possibly our fate as a species.

Saturn V rocket

How many of you have debated fitting rockets to your car? Hmmm, thought so.
In a bit of a departure from the norm, this time I am going to wobble on about the most powerful motive force ever made. I used to think it was the legendary Saturn V rocket that powered the Apollo missions to the moon, but actually it was the Russian Energia – but that was only used experimentally and so apparently doesn’t count, so here are the facts on the Saturn V.
One thing that strikes me about it is its sheer size, at 363 feet tall its only one foot shorter than St Pauls Cathedral and only 6 foot shorter than the assembly building it was made in, a building so big that it has its own weather system.
The rocket was assembled on a mobile platform with the launch tower already fitted, the whole lot is stacked on the ‘crawler transporter’ which is still used for the space shuttle today. The transporter is, as you would expect, big and is basically an oil rig sitting on four giant bulldozers, each of the eight tracks weighs over 50 tonnes.
It wasn’t light either at about 2700 tonnes, mostly fuel, with a payload of 118 tonnes.
The choice of fuel is interesting, well it is to me anyway, the top two stages were fuelled by liquid hydrogen which has excellent power to weight ratio, but is a bit tricky to store and so only gets pumped in when everything is ready to go on the launch pad. The bottom first stage is fuelled by the much more convenient RP-1 which is basically highly refined kerosene which doesn’t leak and explode so easily but weighs more for a given power. There is no air in space so the whole lot uses liquid oxygen to create the ideal mixture. Liquid oxygen is funky stuff, if it soaks into a piece of wood you have something more explosive than dynamite. There was a technician back in the ‘70s at an American university who used to light the annual engineering department BBQ with liquid oxygen, three full sacks of charcoal would ignite, flare off and be ready to cook on in under 3 seconds. He used a bucket on the end of a long plank to deliver it but they have stopped him doing it now. In this country you need an explosives licence to have liquid oxygen, with good reason.
Anyway, back to the subject. Have you ever wondered how you steer a rocket? Well, the nozzle is moved by enormous hydraulic rams, controlled by several computers (all analogue) to keep the whole stack stable, a bit like balancing a broom upside down on the palm of your hand whilst someone lets dynamite off under your feet. Nothing to it really. (For the techy amongst us they vector the thrust angle through the centre of gravity, simples)
That initial blast comes from the first stage and lasts for 2.5 minutes, in that time the rocket has reached 42 miles high and is doing over 6100 mph, it has also got through 2000 tonnes of fuel and oxygen. That’s a rate of over 13 tonnes per second. You need a big pump, a turbo pump in fact, and they look like large jet engines hung off the side of the rocket motor, more about them later.
The first stage of the Saturn V has five Rocketdyne ‘F-1’ engines, the middle one is fixed but the other four are gimballed for steering on one mighty ball joint. When starting it up there is a little more to it than turning an ignition key, first the middle engine is fired up then opposite pairs of outer engines at 300 millisecond intervals to minimise stress on the chassis. When all five were on song they produced over 34 MN (Mega Newtons) of force which accelerated the whole lot at about 1.2g, pinning the astronauts down as if a fat man was lying on them, but this increased to 4g as the fuel load reduced so to limit this crushing force the middle engine is switched off early.
Although thrust force doesn’t really equate to power, if we use the energy released by the fuel to give you a rough idea of the magnitude of this thing it’s about 573 Giga watts or about 770 million horse power. But as I say that is not a sensible way of expressing thrust, it’s just to give you some perspective.
After the first stage finishes and separates from the rest of the rocket, momentum carries it further up to a height of 68 miles before plummeting into the Atlantic ocean, or waste disposal unit as they seem to think of it.
The next two stages are a lot less powerful, but as gravity and air drag reduce you don’t need such a big motor. The second stage produces 5MN of thrust for 6 minutes but raises the speed from 6100mph to over 15000 mph, the final third stage chucks out 1MN and raised the speed to over 25000 mph which is just enough to escape earth’s gravity and glide unpowered for three days to the moon.
These stages used liquid hydrogen as fuel which is much more efficient than RP-1, using Rocketdyne J-2 engines the second stage had five engines and the third stage only one.
More interesting is the first stage F-1 engines which are the most powerful ever put into service. The two turbo pumps that supplied fuel and liquid oxygen were powered by a gas generator providing 55 thousand bhp, it’s basically a really big turbo with a gas generator powering the turbine and the compressor doing the pumping work. The fuel pump delivered nearly a thousand litres per second and the liquid oxygen pumped out over 1500 litres per second at -184ºC. The gas input temperature to the turbine was above 816ºC so the bearings were cooled and lubricated by fuel. In fact the fuel was pumped round 178 tubes at the top of the thrust chamber (rocket nozzle) to stop the whole engine melting.
Each F-1 engine weighed just over 8 tonnes and was 5.79m high by 3.76m diameter
Which got me thinking; if you mounted one in a racing truck chassis it would accelerate at about 50g, instantly killing the driver, and after one second it would be doing about 1000 mph. Don’t try this at home kids.

Opposed pistons

There is a debate as to whether 8 or 4 cylinders are best, but it’s not what you’ve got, it’s how you use it. Apparently. If you look back 100 years you will see all sorts of ideas for novel engines, it sometimes seems a little odd that we have become so used to only using the 4 stroke piston engine.
A four-stroke engine only actually produces power on one stroke out of four, which is only a quarter of the time. Two-stroke engines produce power every down stroke, that’s twice as often, so for the same engine size it should produce about twice the power. Which is nice.
In reality there are some problems with 2 strokes; getting fresh mixture in and the exhaust out at the same time, near bottom dead centre, whist still keeping the ports closed enough to allow a reasonable amount of the stroke to produce power. This is why they need some form of forced induction to push new mixture in and the exhaust out – on bikes this tends to be by feeding the mixture through the crank case and using the underside of the piston as a compressor on the down stroke. But then you need to mix oil with the fuel to keep the crank happy, which reduces power and produces rubbish emissions. The bigger engines, used in military vehicles and such, use a supercharger to do the work instead thus solving the oil problem at the expense of weight.

Genius of engineering.

But how about if we pack more pistons into the same space; the Rolls Royce K60 Range multi-fuel engines put two pistons in the same cylinder, one at the top one at the bottom and a crank shaft at each end. It’s an idea that has been around for some time, one of the greatest exponents of it was the German Junkers company in the Second World War, the experimental Jumo223 engine having 4 banks of 6 cylinders and thus 48 pistons, the larger Jumo224 was 73 litres and produced 4500bhp at 3000rpm but weighed the same as a small lorry.
The opposed piston design only works with the two-stroke system of piston covered inlet and exhaust ports in the cylinder walls, in fact in the Rolls Royce K60 opposed piston engine, one piston uncovered the exhaust ports and the other one did the intake. The two cranks were geared together with an offset of 20 degrees in order to get the exhaust and intake timing right. The top crank thus produced only a third of the total power and drove the supercharger, alternator, water pump and other gubbins so there was only a small proportion of power left going to the bottom crank, so the connecting gears could be quite small and light. Very clever.
A slice of lovelyness

Although there have been attempts at opposed piston spark ignition engines in the past, the problem of getting the spark plug into the cylinder wall without compromising the design of the combustion chamber (formed by the two piston crowns) and cooling system proved to much of a buggerance. So most Opposed piston engines are compression ignition, that’s diesel to you.
The remarkable thing about the K60 engine is the types of fuel it uses, basically almost anything that catches fire, diesel, kerosene, JP4 jet fuel and petrol with and octane rating of less than 80. Remember the octane rating is the tendency of a fuel to go bang when you squash it (ie knock), so a low octane fuel will burn in a diesel engine but a high octane one won’t, or at least not very well. Of course this does mean that the power per litre has to be compromised in fine British tradition.
The K60 was a relatively small engine, at 6.57 litres and produced 240bhp at a crank speed of 2400rpm, but because of the way the two cranks were geared together the output flywheel would be doing 3750rpm so that it could directly replace the older B80 range of straight 8 cylinder petrol engines in things like the 432 armoured personnel carrier. It was also used in the Swedish S tank along with a 300bhp turbine engine, as tanks go its well worth looking into, really funky.
Amusingly the K60 was marketed as being light, as it only weighed 757kg! but compared to the Leyland L60 engine, which was a flat version of the same thing and bigger at 19 litres, which was well over a ton the K60 was a feather weight.
The secret is in its long studs. Although that sounds like the title of a spam email, it is the same principal that was used decades later on the Rover K series engine. The crank main bearing caps are held on with studs that goes right through the engine and out the top, in the Rover case they held the cylinder head on, in the K60 case they hold the top crank bearing caps on too and tie the whole engine together very well. Making a very reliable engine.
In order to get fresh mixture into a cylinder that was still venting the exhaust gasses, a Roots supercharger was fitted. Later versions also had a turbo, you still need the supercharger because otherwise, because the turbo makes no boost at idle, you will never get the engine started. But once on song, the turbo added more boost and improved power and efficiency in the traditional turbo diesel way. Supercharged and turbocharged, now that does sound like a good thing.
Now, me being me, I have wondered if I could make up a home brewed modern equivalent, there is after all a lot going for opposed piston engines, for a start you lose the weight of a cylinder head. Maybe using parts from two BMW 6 cylinder diesels welded together. The standard 4 stroke can be tuned to about 300bhp, so 2-stroking it could make maybe 500, then having the two nailed together we might be in the 900bhp range. The engine might weigh less than 400kg too which, compared to my old Jaguar V12 at 350kg, isn’t too bad. Hmm, a 12 piston opposed diesel Jaguar with 900bhp and really good fuel economy – tempting. It is of course a really stupid idea and should only inhabit the area near a bar. Mind you, I bet there is someone out there who could do it..

Testing Tyres – A Life on the Limit.

It’s a stunningly beautiful day in the south of France, mountains in the background and a clear blue sky. Standing before me is a tall, smartly stylish man, smiling and confident with a tan of someone who works outdoors. The only clues to his extraordinary life are his shoes; subtle grey low cut racing boots. Oh, and the sound of tyres squealing all around us.

Man, Machine and a selection of the best roads in the world,

The man is Jérôme Haslin, chief test driver for Michelin and it is his verdict that shapes the performance of some of the most exciting cars on the planet, a role he takes very seriously and clearly enjoys with a great passion. Not surprising when a typical day will involve up to 8 hours screaming sports cars round the best tracks in the world from Magny-Cours to the legendary Nurbergring; “Its very variable, today I have only driven about 3 hours but when I am with a client, such as Ferrari or Porsche, I will be all day in the cars”. And the list of cars he has tested reads like a dream garage, Maserati MC12, Honda NSX, F3000, Ferraris, Bugattis and all the current Porsches, he calmly describes going flat out in the Veyron as “a nice experience”.
Not that he has all the fun to himself, he is in charge of 25 other test drivers including 2 for motorbikes, including MotoGP, 10 for trucks, and even one for tractors. The 450 hectare test centre at Ladoux in south eastern France incorporates 19 different test tracks, including a precisely irrigated wet handling circuit, a dry 2.8km handling circuit and a 7.8km high speed circuit with banked corners.
But he didn’t get here by chance; “my passion has always been driving, so after I graduated with a degree in mechanical engineering I looked for jobs that had an element of driving”. He joined Michelin in 1992 as a tyre design engineer, spending two years getting to grips with tyre technology and performance. Then he spent 6 months solid training to understand test methods and hone his car control skills, spending hours sliding round the practice circuit; “I started with a BMW 3 series which is a very nice car to learn on”.
Driving on the absolute limit has to be second nature to Jérôme so that he can make subjective assessments and perform precise tests without being distracted by the business of controlling the car. “It’s a bit like wine tasting, its sensorial analysis, but you need a good memory because of the time for tyre changes; imagine tasting one wine then having to wait 50 minuets before tasting the next!”.
During his training he spent hours cornering with a G meter on the dash, getting familiar with the feeling of different side G forces, the result is that his gut is now a sensitive instrument, allowing him to perform exact manoeuvres instinctively.
To get a little insight into his fabulous job, Michelin have organised a morning’s fun on their test track, armed with a Porsche Carrera 2 and three different sets of tyres. Jérôme will show me what he does and then I will have a go! What can possibly go wrong?
The Office.

I have to confess that I have never really liked rear engined Porches, the lift off oversteer is reminiscent of early Austin Metros and for the money I would rather have a car with the engine in the right place. OK, that’s just me then… However, in this case it makes the ideal choice to show how tyres can transform a car’s handling, and as it turns out the transformation is amazing (see panel), and more importantly gives an insight in to Jérôme’s average day in the office.
First stop is the 4.1km wet track, with standing water controlled to 3mm, it makes for a fun day out for any petrol head. As soon as Jérôme drives onto the track we are going sideways at motorway speeds whilst he calmly tells me about some characteristics of these tyres. But my attention is grabbed by the sturdy looking Armco directly in our path, “ah yes, that’s the one place on the track it is not safe to come off, you must be careful here” he says whilst power sliding past it.
In all my years developing cars I have never known a driver so talented as Jérôme, he is controlling the slides so precisely that photographer Stuart is totally confident standing on the rumble strips on the apex of the hairpin. Not only that but as Jérôme performs balletic manoeuvres he is able to describe in detail the sensations that are a key part of his tests, “on the wet circuit we are looking for consistent fast lap times with little slip, but I think your photographer wants more action shots, yes?”. Weeeeeeeee!
Next we head for the ‘Circuit grande vitesse’ and take the slip road onto the 1.5km straight, then power onto the banked corners where Jérôme suddenly yanks the steering and we head rapidly towards the Armco. “As we put in a rapid steering input at high speed, we observe how long the car takes to respond” he calmly says before yanking the steering the other way just in time to avoid making the local news. Next, he holds the steering wheel at a smaller angle and observes how long the side force takes to build up, I find this difficult to concentrate on as there is a concrete bridge coming rapidly into view and we are very slightly sideways towards it.
Luckily he straightens the car up in time, and then proceeds to demonstrate what happens when you let go of the steering on a banked corner; “for each banked corner there is a neutral speed where the force of the car pushing outwards is balanced by gravity” and we go round staying perfectly in lane.
He accelerates hard onto the straight and we do the whole ‘experiment’ again, but much faster, swerving at 250kmh! After a blistering lap we leave the slip road with the brakes squeaking and smelling of ‘hot’.
Next stop on the fun fair is the handling track, 2.8km of twists and turns which is officially sanctioned by the FIA for F1 testing. On the way there, we pass the wet circuit just in time to see two 17 tonne trucks perform synchronised drifting in a cloud of spray!
As we wait for a bike test to finish on the handling circuit, Jérôme explains what is coming up; “first we run at a fairly constant speed staying on the middle of the road, just getting a feel for how the tyres perform, seeing where it under/oversteers etc.”. Just then the prototype bike screams round the corner, the rider seems to have his elbow down, never mind his knee! As he vacates the circuit his enormous grin confirms that is a great place to work.
As we ease on to the circuit Jérôme pegs it at about 4000rpm in fourth gear and we follow a faint white line in the middle of the road, noting how the car responds to turns without the complication of accelerating or braking, it’s a very strange way to go round a track but very informative. Next Jérôme steps up the pace dramatically for three timed laps, by crikey he is good; hitting about 217kph before on the limit breaking for the 2nd gear hairpin. After three laps flat out, Jerome suggests that I have a go, top banana!
Avoiding the temptation to just drive very fast, I tried to perform some of the tests Jérôme had shown me, after all I have had two decades in the car industry, test driving everything from Fiestas to Bentleys, surely this should be easy? No chance, its worse than the old rubbing your tummy whilst patting your head challenge, whilst concentrating on G force in one corner I missed the line in to the next, and as I discovered my talent deficit we drifted towards the grass, Jérôme casually commented “of course every tyre has its limits”!
After a few laps I have a profound respect for Jérôme’s talent, as we slow down and exit the circuit I ponder what it would be like to live this life. In the calm of the car park under the clear blue sky, with smiles all round, Stuart asks whether I would want Jérôme’s job, ‘without doubt mate, without doubt’.

Ready for battle.

The Tyre storey
As always, tyres make all the difference and if you have a Porsche then you may find the results interesting;
The standard Michelin Pilot Sport tyres work really well in the wet and equally well in the dry, but backing off when turning into a corner brings the back end round in the traditional Metro manner.
Changing to Michelin Pilot Sport Cup, the choice tyre for the Porsche Cup races, and immediately the grip is noticeably higher, we are entering corners in a higher gear. But at the back the grip is increased even more than on the front with the astonishing result that the lift off oversteer is virtually eliminated, it as if we are in a different car. Obviously you can’t have everything and wet grip is more ‘exciting’.
Finally we tried the full race slicks, here the front end grip is amazing and turning into corners at full tilt inspires confidence, grip at the rear is increased again but not as much as the front resulting in a small amount of lift off oversteer, but only at race speeds. It goes without saying that this tyre should not be even tried in the wet!
Lap times tell all, 1min12.33sec for the Pilot Sport, a quicker but close 1min11.35sec for the Pilot Sport Cup and a blistering 1min08.78sec for the slicks. To my mind the Pilot Sport Cup tyres, developed for the Porsche race series, deliver the nicest package for the sportier driver, OK so they are a little worse in the wet, but if it was raining why on earth would you decide to drive a Porsche 911?

The workshop files, like the X Files but without the probing.

Sockets and spanners. We all use them, yet there is more to sockets and spanners than meets the eye, common problems result in rounded bolt heads and lots of swearing.

Spanners make rubbish goggles.

A bolt head’s corners are its weakest part, and yet many ‘economy’ spanners or sockets apply all the force through this small area, loose fitting tools make this problem much worse.
Good quality ring spanners and sockets have the corners radiused out so it is impossible to round the corners off the nut or bolt. This design has been taken a step further in recent years with spanners that have totally convex sides.
A bi-hex tool has a 12 cornered pattern made from two hexagons superimposed and is easier to get on to a nut or bolt when there is a restricted access. The down side is that the force is concentrated closer to the corners, a single hex is generally stronger, and less likely to round off.
Open ended spanners only apply force to two corners of the nut or bolt, so they should only be used for easy jobs. Modern ratchet spanners are amazingly strong and useful on those jobs where you would otherwise be moving a fraction of a turn at a time.
When delving into the gloomy depths of a classic engine bay it is not always possible to get straight line access, luckily there are a range of universal joints available to save the day. The cheapest option is a simple Hooks type joint, but these can lock up at steep angles and can flop to one side when force is applied.
There are also flexible drives based on contra wound springs, the thicker ones are less flexible but can take more force.
The ‘wobble drive’ uses a profiled drive peg that allows the socket to tilt. Obviously the reduced metal on the drive means that it is not as strong, so it is wise not to use a breaker bar with them. Most wobble drives have a shoulder cut into the base of the drive peg so that the socket can be pushed a little further on to engage rigidly.
Using an extension bar creates a force making the socket topple over. The way round this is to use an extension long enough so that you can support the shaft properly with your other hand and counter act the toppling force. And when pushing a tool with force always use gloves and an open hand to avoid smashing knuckles.
Torque wrenches need to be accurate, the tolerance should be better than ±5%. Cheap torque wrenches that don’t have any such data available should be avoided. If you are just starting out in the wonderful world of mechanicking, use a torque wrench on every job until you get the feel of how much force to apply.
Adjustable wrenches, hmm, what to write about them. generally the advice is avoid, get the right spanner instead,although a good quality item can get you out of trouble in an emergency.
Every socket set should have a long ‘power bar’ also known as a ‘breaker bar’, this not only makes jobs easier but safer too.

One of the big changes over the last two decades is in metal quality, years ago a bargain basement socket set would most likely fall apart the first time it was used in anger, but now even relatively cheap sets can be robust enough for home use.
One thing to look for is the words Chrome Vanadium, or simply the letters CV. This is an alloy steel that combines hardness and strength, it has a bright silver finish just like stainless and needs no other surface treatment. Poor quality tools use ordinary steel and either polish it or plate it in chrome which can flake off causing nasty cuts.
Conventional sockets and spanners are hard, and therefore brittle, to avoid deforming. But sometimes a stubborn bolt needs an extra whack to get moving, impact sockets are made from mild steel, so they wont shatter like conventional sockets when hit, but being softer it needs a much thicker wall to maintain strength. Impact sockets are usually etched matt black or painted, the raw steel would corrode and chrome plating would chip in the impact.

There is more to doing up nuts and bolts than meets the eye. If the threads have corrosion then there will be much higher friction, so the bolt will be harder to do up and you might not get the correct clamping force. Most tightening torques are based on clean threads and sometimes with lubricant, but either way corroded threads need to be cleaned up or replaced.

A lot of classics use bolts that are far to long for the job, the exposed thread will corrode and grind past the nut when undoing it, starting easily but getting tight again. So clean up and lubricate any exposed thread before attempting to undo it.
Long cylinder head bolts in alloy blocks can seize at the bottom, allowing the bolt head to turn and spring back without coming loose. Penetrating oil may get past, so leave it to soak for a day or two, or leave a constant force on it for a long period of time by clamping the spanner in place.
Sometimes the only option is to snap the head off and drill out the remains of the bolt. But beware of shards of sharp metal hurtling through the air.
If the bolt just simply refuses to move at all it may be possible to shock it free by using an impact driver. Never hit a spanner, they are brittle and also have a tendency to ping off with painful results.
Heat can come to the rescue too, or cause even greater chaos, be careful not to damage other components in the area or set fire to the car. Heating a nut causes it to expand and so loosen its grip, and conversely freezing the bolt makes it shrink away from the nut.

Rounding off
Every workshop needs a set of self gripping wrenches, aka pipe wrench or Stillson. As ever quality counts, the teeth need to be fairly fine and should be hardened or chrome vanadium. Cheap soft steel items slip making them useless. If it is difficult to get the tool started, hold the upper jaw on to the job whilst starting to apply load until it bites.
Depending on how worn or corroded the nut is, it may be possible to use a slightly smaller socket to get it undone, mixing metric and imperial can sometimes do the trick, or force a smaller cheap mild steel socket on.
The final option is to weld a piece of scrap metal on to form a leaver, but be careful not to accidentally weld the nut onto the bolt.

Here is a good rule for you; if a job is very hard work then you are doing it wrong. If undoing a bolt results in you heaving as hard as possible on the spanner then you need a longer spanner. Get the right tools and learn how to use them, then life gets easier.

Why modern diesels are so good.

This is a little something from the archives, a conversation with Will from PPC magazine tackling some common diesel questions.

1 What’s that bloody horrible noise?

Time to start using big words. The fundamental difference in combustion between petrol and diesel is that in a petrol engine the mixture is prepared in the intake then breathed in through the inlet valve as a ready to burn mixture. In a diesel only air goes in through the inlet, it is then compressed in the chamber (sometimes reaching over 600°C), then diesel is injected into the chamber and ignites in a stream of fire and takes most of the power stroke to burn.
At idle, however, only a little bit of fuel goes in, there is a short delay whilst it soaks up the heat then it goes bang all at once in a very short time. This makes a much sharper rise and fall in pressure and a harsher noise than an equivalent petrol engine.

A Diesel engine earlier today.

But you might be surprised to hear that at full load, there is very little difference in combustion noise between petrol and diesel and some times a diesel can even be quieter!
But the most noise you hear from conventional diesels is not from the combustion at all, oh no, its from the fuel injection pump and injectors. The massive pressures needed to squirt a fine mist of fuel into a compressed cylinder of hot air require a powerful pump which has its own pistons thumping up and down. A twenty year old design may thump the fuel pressure up to 250 Bar every stroke.
When testing the pumps on a rig we have to wear ear defenders, its that loud. There are times during a cars development when we need to measure just the combustion noise and then we have to wrap the pump, high pressure pipes and injectors in lead sheet to keep them quiet.
Funny old world.

Things are very different now, the current generation of diesels use multiple injections in each cylinder even to smooth out the pressure rise and fall during combustion in a way that Rudolf Diesel could only have dreamed of, coupled with three piston pumps which provide a smooth regulated fuel pressure and are inherently quieter.

2 Please tell me about LPG and diesel.

It’s a good thing.
No, really, it is.
The effect is very similar to putting Nitrous on a petrol engine but with improved fuel economy too.
Injecting up to 40% LPG into a diesel engine does a number of things, the main one being that it helps the flame to propagate through the whole mixture and actually increases the efficiency of the diesel fuel (more molecules get burnt in the chamber). It also has energy of its own to contribute.
About 5% at idle will quieten combustion noise, but at part load cruising conditions you can make up to 40% of the total fuel going in LPG which boosts combined fuel economy by more than 10%.
It also has the effect of effectively illuminating turbo lag.
The down side is that unless the system is calibrated properly to your application then you risk the engine pinking and associated damage.
I did develop a simple mechanical system years ago, before going digital, but it is impossible to get the fuelling right under all conditions and engine damage is almost inevitable.
If you use a well mapped digital system then the benefits are massive, huge power increase (one of my first attempts was with a Sprinter van which went from the standard 110bhp to 195bhp and masses of mid range torque) and it gets cheaper to run.
But beware, if you run out of diesel at high loads and try to press on with just LPG then the engine will pink like hell and almost certainly will melt. Don’t do it.

3 My understanding of common rail injection is that, unlike the older
systems with a pump that squirted fuel into each cylinder in turn,
common rail has a similar architecture to petrol EFi systems. A high
pressure pump feeds a common fuel rail and the injectors are fired
electronically (on new systems) or by a lobe on the cam on older ones.
Have I got this right?

Pretty much, the fuel rail pressure is in the region of 2000 Bar on some engines, a Piezoelectric crystal is used instead of a solenoid for the injectors, they run at up to 160 Volts and move a very small amount but allow us to control up to 5 individual injections for each combustion cycle. A small amount goes in to start warming things up and start a gentle pressure rise, then a slightly longer one etc. then the main body of fuel is injected, allowed to combust and then a few more small injections just to help finish off the combustion, help emission control and allow the pressure to drop gently.
This amazingly detailed control of the combustion process allows the engine to run at its best potential under the full range of driving conditions. This in turn allowed the valve train and ports to be optimised for air flow rather than older engines which used restrictive high swirl designs to improve combustion. And this allowed for greater turbo control, we could now muck about with injection timing and volume to tweak the flow of exhaust gas, helping to reduce turbo lag, which coupled with running higher boost pressure using better turbos that have a greater flow range give the engine a much wider torque band, pulling strongly from low revs right up to the red line. All these things together are the main reason modern diesels are so powerful and yet still economical.

Just to complete the historical picture some engines used Unit Injectors which are slightly different, they have an individual piston pump for each cylinder, running from an extra cam shaft. A solenoid is used to open and close a bypass port which lets the fuel escape back to the tank. If the piston is pumping and the port is closed then the pressure rises until the injector needle is forced off its seat and injection commences. It was the best technology until Piezo injectors were invented.

4 Why won’t Diesels rev? Is it because the fuel won’t burn quickly enough?

Every fuel has a certain burn speed, petrol is about 20 to 40 meters per second (40 to 80mph) depending on mixture strength, exact fuel composition and about a million other factors. Diesel burns about 18% slower, ish. So if the engine goes too fast then the mixture is still burning when the exhaust cycle starts which is pointless.
Another factor is that older diesels needed lots of turbulence in the chamber to mix the fuel spray jet with the air and so had very high swirl inlet ports which can be restrictive at high speeds.

5 Why are they inherently more fuel-efficient? Is it simply because of
the much higher Compression Ratio?

The Compression Ratio is indeed a big part of this (though technically it’s the expansion ratio that’s important for good thermal efficiency), but there are also a number of other important factors too.
A simple diesel has no throttle, so there are no losses from dragging air past a blockage at part load, unlike petrol engines.
Then there is the fact that it always runs with a very lean mixture. The cylinder fills with the same amount of air no matter how much welly you give it, your accelerator pedal only changes the quantity of fuel injected. Because the fuel is injected directly in to the chamber it spreads from the injector nozzle and mixes with more and more air until it reaches the right mixture strength to combust, the exact process is a lot more complicated than that but you get the idea.
The improved efficiency is most pronounced at part load, cruising gently and driving round town. At full chat there is much less of a difference between the two engines. If you measure efficiency as grams of fuel used per kW hour of energy (just like on you electricity meter on your house) you will find that at best petrol engines can get down to 250g/Kwh and diesels manage to get down to 240, for cars that is, not a huge difference.
Last but not least is the fact that although diesel fuel has about the same energy content as petrol at 42.5 Mj/Kg (that’s mega joules of energy per kg), is a little bit denser at 0.85kg per litre as opposed to 0.75kg/l for petrol, so because we buy fuel by the litre and not by the Kg you get better value for money (energy/litre) from diesel.
All these factors add up.

6 Know anything about 2-stroke diesels? I used to go to school on a bus
that was ancient even then (this was 1978). I think it had a Comer
engine but either way it was a 2-stroke supercharged (I think) diesel.
I think it had opposing pistons and was all very weird. But it sounded
good at full chat.

The Comer engine is just stunning, find a cut away diagram and just marvel at it.
Two stroke’s need some sort of pump to force the air into the inlet port, older style little bike engines use the crank case to do this, as the piston goes down it compresses the mixture in the crank case then unveils the inlet port so it all rushes in, the problem is you get all the crank case gas and oil burning in the engine, hence the trail of smoke.
Big two strokes tend to use a separate pump (supercharger) to do the job so they don’t have the smoking habit.
The comer had three cylinders lying on the floor; each cylinder had a piston at each end connected to a bell crank type con rod to a central crank shaft mounted above the cylinders.
Madness but elegant and a very low centre of graffiti.
Other opposed piston two stroke diesels include the Rolls Royce K range multi fuel units fitted to 432 armoured personnel carriers and Scorpion ‘tanks’ plus the wonderful Napier Deltic locomotive engine which is like a diesel Toblerone.
Two stroke engine produce power on every down stroke as opposed to every other down stroke on a four stroke engine, so you get more power for a given size or weight of engine. This makes them very popular for high power applications, Detroit Diesel make a splendid range of supercharged two stroke diesels and sound absolutely mad!
Some times a turbo is added as well, but there still has to be a supercharger or else you could never get inlet pressure to get the engine started.

I hope this gives a little illumination, as with most things the truth of the matter is rather complex and the above replies are massive simplifications, but a little knowledge is a dangerous thing, and after all dangerous is how we like to be.