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.

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.