How much power does a sports car need?



I was testing a compact SUV the other day, it’s spec sheet fits in nicely with the current competition; about 240bhp in a 1400kg car, 4WD and 0-60 in the region of 7.9s. Although this may not be earth shattering performance by modern standards it set me thinking, about two decades ago I was working on a car that some of you may of heard of; the Escort Cosworth.

Now the Cossy set the world alight with its ‘blistering performance’, even that bloke Clarkson had one of his own and spent far too long telling everyone. Part of the Cossy legend comes fro the fact that in full rally cross tune it could hit the dark side of 600bhp, but even the standard version was in reality rather quick.

But now the Focus five pot has more than 300bhp and luxury saloons must have 500bhp to be a serious contender. Things have clearly moved on, but surely an old quick car is still a quick car? If I hopped into a Cossy today would I be bored rigid with it’s hum drum performance?

So I did a highly un-scientific poll on Twitter, asking people what felt quick to them, and the results were remarkably consistent, although that might just be an indication of the type of people who follow me!

Allegro fan extraordinare @OneCarefulOwner commented “the goalposts have moved in a major way; my Maxi 1750HL had a blistering 96bhp, nowadays small diesels have more grunt.”

@racing_waiting pointed out that defining quick was a well trodden path “tricky question, drivers republic struggled, imotor struggled, road my previous mag stuggled.”

On the subject of the old XR3i @HairyCalahan observed “times have changed. expectations too. xr3i fine for it’s day”

But getting down to numbers @vHenryk considdered that “pretty much. A ‘sports car’ doesn’t have to be a ridiculously expensive 0-60 in less than 5 secs thing to deserve the name.”. Whilst @torquespeak said “Puma convinces me anything above 120 has a decent shot. 8 secs to 60 not first degree rapid but a hoot on the twisty bits!”

Of course power and weight are only part of the storey as student and car nut @MrPA sugests “On a decent road anything can be fun. I have a few corner-filled favourites which are brilliant in my mum’s 1.2 Clio (75bhp!).” a fair point and one echoed by @cotswoldracer “Indeed , my old AX GT 700Kg & 85bhp , and going by memory about the same as my 145 in terms of acceleration (8ish secs to 60), my Alfa 145/950kg/150bhp quick-ish , another 35 bhp would make it even more fun :)”

@carpunk observes the importance of weight in its own right “Guess 100hp in a 1000kg car will always feel much quicker than 250hp in car 2x the weight because of inertia, braking mass etc “ and @jonbradbury agrees “I think modern expectations have increased, & so has most weights. Though 160hp in 1T 944 shifted lot better 115hp Gti & the 115hp GTi shifted better than the 115hp XR3i.”

The consensus seemed to be that a ‘sports car’ of between 1 and 1.5 tons should have between 180 and 250bhp.

Which brings up some interesting points, firstly that a lot of ordinary family cars are actually high performance sports cars, and it may well be that the only reason that they are not regularly parked in hedges and Armco is the astonishing amount of technology dedicated to combating incompetence behind the wheel.

But going back the that point about the way cars feel, this fantastic driver assistance seems to have come hand in hand with a duller edge to the driving experience. Back in the day a sports car would engage and entertain the driver, not only with its performance but also with its ability to snap back and slap the unwary in the startled face. Putting your foot down in a high powered car not only thrilled but also surprised many a driver when glancing at the speedo to see the needle significantly further round than expected. Over enthusiastic cornering could result in the car suddenly swapping ends or having less wheels on the ground than is healthy. Motoring enthusiasts call this sort of thing ‘fun’, but unfortunately normal people call it dangerous, and so because there are more of ‘them’ buying cars than there are ‘us’ cars have become less dangerous, and sometimes less fun.

But from an engineering point of view fun and safe can co-exist. Some manufacturers have cottoned on to the fact that whilst safe and dull is best for the mass market there is still a significant market for thrilling cars, and having driver aids set to only come in when disaster is otherwise inevitable yet allowing a reasonable degree of sideways progress makes good sense.

For instance if you turn off the traction control on a Jaguar XKR you can light up the tyres and do doughnuts, but you will still struggle to accidentally oversteer backwards into the vicars rose garden because the system is still active and helping the driver achieve their intended trajectory. I have driven one with the traction control completely removed, and to say one needs ones wits honed and ready for extreme service is an understatement, it’s not fun on a wet B road – it’s simply scary.

Maybe 500bhp is fine when controlled by modern electro-wizardry, but has the same thrill factor as a raw 200bhp in a car with no aids at all. So how much power does a sports car need? Well it would seem the definitive answer is ‘it depends’.

How brakes work

Brakes are all about heat, and ditching as much of it as quickly as possible, they work by converting the cars speed energy into heat energy which is then taken swiftly away in the air streaming through them, in theory. But a big car at high speed has an awful lot of energy; for instance getting a big car to do an emergency stop from high speed might put the equivalent of a thousand bhp through the brakes make the discs glow red.

There are two basic types of brake, drum brakes get their name from the drum of steel with curved shoes inside that are pushed outwards against the inside of the drum when the brake pedal is pushed. These can be found on the back axles of cheaper cars and are quite frankly a bit pants; the braking force is limited by the drum wanting to explode, plus the pistons are small and the pressure pushing the shoes out into the drum is similarly small.

By comparison disc brakes can exert a much higher force onto the disc without risk of it failing.

It uses a disc with a set of pads held in a calliper that are forced against both sides of the disc when the pedal is pressed, generating much more force.

In both cases the disc or drum part is attached to the wheel hub so it rotates with the wheel and the pads or shoes are held stationary on the axle, or strut, or what ever dangly bits are attached to the suspension.
All brakes work by friction, pressing a pretty darn tough pad of friction material against the spinning metal, the harder the friction material is pressed against the metal the more friction is produced and the greater the braking force.
Brake systems use a special type of high temperature hydraulic oil to drive the pistons which push the friction material into the disc or drum. At the pedal end there is another piston in the master cylinder which is connected by hydraulic brake pipe to the slave cylinders at each wheel. In some cars the brake force is artificially increased by a servo directly connected between the brake pedal and the master cylinder, this uses vacuum from the intake manifold to move a large diaphragm when the brake pedal was pressed, as the pedal moved down small holes in the servo control section are progressively uncovered which applies more vacuum to the diaphragm which in turn applies a greater force to the master piston of up to four times the force at the pedal.

Some cars with Anti-lock Brake Systems (ABS) use a powerful electric pump to do this instead. The ABS system measures wheel speeds and if it detects that a wheel is slowing down faster than a safe limit then it knows that that wheel is about to start locking up, so it lets the brake pressure off the individual wheel by opening a solenoid valve in the ABS valve block, just for a tiny fraction of a second until the wheel frees up just enough to know it wont lock. You can feel this when it happens as a sort of buzzing or vibration under the brake pedal. ABS allows maximum braking force without the risk of skidding. But if you are going to fast then you are still going to crash no matter what the brakes do.
The fierce heat generated from heavy braking has to be dissipated into the air which is why race cars have ducts taking fresh air from the front of the car to the disc centre, the hot air then has to go somewhere and the design of the wheel should allow it to escape readily. To get more heat into the air some discs are vented with radial channels cast into the disc to draw air from the centre outwards, some discs also have small holes drilled through for even more ventilation but these can lead to cracks starting unless they are made very well. Groves on performance discs can help remove the tiny gas layer that build up between the pad and disc sometimes and increase pad bite, the down side is that they can increase pad wear when used aggressively.
The brake size needed on a car depends on its weight and how fast it is likely to go, more powerful cars can more readily get up to higher speeds they need bigger brakes. Bigger pistons and a larger diameter disc make better brakes. Also if the brakes are going to be used for long durations, such as when racing, there is less time between brake applications for them to cool down adequately, this is where vented disks can be a real benefit.
All that heat soaks through the system into the brake fluid and although it is engineered to work at these very high temperatures in extreme cases the temperature can get high enough for the oil to boil, this generates gasses which compress easily and make the brake pedal feel very soft. This is brake fade and in really bad cases the brake pedal can sink to the floor with very little braking force generated, pumping the pedal up and down a few times can sometimes help but basically if the brakes fade on a race track then the standard procedure is to crash. That is why on roads with long descents the car’s speed should be controlled by using a low gear and engine braking rather than holding the brakes on for extended periods.

Most brake fluid absorbs water which boils and fades much more easily which is why it must be changed every few years to stay safe. Silicon based fluid is different and doesn’t absorb water but moisture still pools inside the system and needs flushing through every few years, it’s also a bit more squashy than mineral fluid making it unsuitable for fast acting ABS.

Brakes are often overlooked and any wear only becomes apparent at the mot or in an emergency stop. The trouble is that they have a hard life and can disintegrate with the friction material splitting off the steel backing or wearing down to nothing unnoticed, and they usually seem to work fine right up to the point were they don’t work at all and you crash. Maintenance and regular inspection is vital.

Larger brakes with a greater surface area to dissipate the heat into the air can cope with harder use but very large brakes need large wheels in order to fit. But all the force generated by the brakes has to be transmitted into the road by the tyres, so if the brakes are already capable of braking traction then there is little point upgrading them before upgrading the tyres. As ever the best solution depends on how the car is to be used.

The Future of Journalism

Technology is fundamentally changing journalism and will ‘kill off’ the traditional idea of a journalist, or so I’m told.

If you think about it the traditional model of journalism has a very few journalists talking to the many readers much like the Queen addressing the nation, but with more queens. This may be because the traditional methods of mass communication, papers and books, was very expensive, time consuming and required specialist skills. But also because a small elite had vested interests in controlling information to a greater or lesser extent.
However now anyone can communicate to potentially the whole world, more or less for free. Everyone is a journalist, albeit not necessarily a very good one.
First the internet democratised information flow, but now mobile phones are the main information sharing method for the new generation. The devices are small, portable and cheap, you can view content in private or share with friends very easily. Content can be shared via the phone network, the internet or directly via Bluetooth, so people can share localised information within their own clique, forming their own virtual information hub. I noticed this particularly when I was teaching engineering to 16-19 year olds, they shared videos, music and information on phones leaving the internet as a secondary source, TV and magazines hardly got a look in.
Images are often a large part of content, and newer innovations such as iPad and smart paper will be welcomed, but the handy small screen phone device still has the winning formula for most.

So thinking that in some way controlling the internet will control information flow is wrong.

I became a full time journalist only a few years ago, but I am very aware that the life of that role is limited, and maybe in less than ten years it may have completely eroded.

But even with the need for a ‘speaker’ removed, I think there is a natural human tendency to elect locally respected sources of knowledge. Every web forum has one member that everyone turns to for advice.

So in the future there may still be a role for a well informed and competent communicator, the trouble is from an practical point of view that there is no intrinsic method of financially rewarding this role; information is fairly free now and hopefully there is no going back. We are all less inclined to pay for magazine articles when we can read it for free on the web, and despite the huge amount of dross and misinformation that’s about there are still plenty of well informed bloggers who report events very well, some post excellent photos and videos too.

Currently there is still a place for magazines and tv stations, because of the uncertain and variable quality of free media we need somewhere apparently reliable to turn to. But as social networks establish, an reliable free sources are clearly identified, this need will transfer from the paid for media to the free.
We live in a time of great change, traditional roles and social models are being erased from the ground up, content providers such as magazines and tv companies must work with this to make new opportunities, to resist change is to invite disaster.
Me, I’m just trying to pay my bills, and if I want people to carry on paying for my words then I suppose I will have to find something more valuable to say.
Ralph Hosier
Engineer and writer.

Engineers and ‘Designers’.

You may be surprised to hear that there is not always perfect harmony between so called ‘designers’ and the engineers that actually make a car reality.

In fact even the word ‘designer’ is contentious, for what actually is a design? Is it a general sketch of the outside of the car or is it the detailed drawings that parts can be made from? Taken to extremes could I draw a picture of a blue box with a flashing light on top and say I have designed a time machine? Clearly not, but at the other extreme is the chap who draws out the blueprint for a gearbox support bracket a car designer? Again clearly not.

So what is design? It turns out to be a word that is used to mean subtly different things to different people, the dictionary really doesn’t help either with definitions varying from ‘a drawing that shows how something is to be made’ to ‘the general form or arrangement of something’.

And if you think about it the same vagueness exists for the word ‘engineer’ too, in my profession an engineer is someone with a degree in engineering who uses science to solve technical problems in order to create new technology. It’s a complex job with a good mix of practical and academic skills, in other countries such as Germany a professional engineer has the same social status as a doctor. But to British Gas an engineer is the bloke who fixes boilers. So when I create a new thingumyjig after deciding its form and function am I an engineer or a designer?

Maybe it’s ‘engineering design’….

If creating the drawings and working out the form and function is design then it could be argued that what the traditional car ‘designer’ does is actually styling and not design at all.

Either way the few people in the crayon department get lots of credit and go to posh shows to drink bubbly, whilst the many who toiled long hours wrestling near impossible problems in order to actually create a car simply get rewarded with more work. No champers for us just quiet anonymity, although to be fair that’s the way most of us like it.

The tension between the two departments stems from ‘designs’ that make the engineering either difficult or impossible.

In the late ’90s I had the privilege of working at Bentley on ‘Project Bali’ which was the successor to the Continental R/T and would eventually become the Continental GT. The designer there was a very talented chap by the name of Simon Loasby, back then he had to use traditional clay modelling on a rolling chassis made of girders. His studio had the full size clay in the middle and all round were inspirational pictures of older Bentleys and all sorts of stylish items associated with sophisticated high society, it was quite a wonderful place to be, even if rather chilly in the winter months due to the feeble gas heater left over from the war!

Anyway, he created a truly beautiful shape, not entirely different to the car we see today but somehow a touch more elegant. I went to look at it every few weeks as it evolved because I was working on bits of the engine design and crucially wanted to make sure the airflow through the radiator and charge coolers would be enough to let the engine meet the power targets. Critically this means that the apertures in the front have at least the bare minimum area to do the job, but also that the design allowed the hot air out of the engine bay. If the air couldn’t get out as fast as it got in then it backs up, the flow reduces and the engine overheats, so it’s quite important.

Initially the car had nice big air scoops at the front for the charge coolers and a very useful set of side gills to let the air out, I did some flow calculations and all was well.

Then the style changed, the front smoothed out, the holes got smaller and catastrophically the gills went! Undoubtedly the car looked smoother, but did it need to? And now we had to design for the air escaping underneath, which generates lift at high speed and never works quite as well. Simon knew what shape he had to design, and I knew how much air had to go through it, but the two didn’t go together and long conversations ensued.

But before we could go any further on that project the company was sold to a variety of German companies and the whole design was taken over by some other people with stronger accents.

My point here is that both Simon and myself had valid points that contradict each other. Engineers rarely admire ‘designers’, but often study with great enthusiasm the works of great engineers instead. As an aside at Crewe back in the day a Rolls Royce was commonly abbreviated to a ‘Royce’ rather than a ‘Rolls’ because Henry Royce was the engineer.

Designers sometimes complain that engineers keep saying no to everything, and engineers may complain that designers simply don’t understand the implications of their design. So who is right? Well as much as it pains me to say, probably a bit of both.

Engineers have to design a car that works in the real world, restricted by the laws of nature, legislation, finance and time. But designers have to create a shape the will engage the minds of customers, and most customers don’t give a fig for what’s under the shiny paint as long as it works. Occasionally in big companies the two groups are unwittingly assigned briefs that will inevitably result in conflict.

Sometimes in smaller teams these traditional roles are blurred, and it seems to work better that way, the McLaren F1 road car is a prime example.

Have a look at the original engineering prototype cars for the Range Rover back in the ’60s. They, Spen King & co, recognised all the key features a customer would want, packaged it all together in a way that worked very well indeed but looked very slightly unpleasant. Add a touch of styling and the car was transformed, but without ruining the engineering. That is, I think you will find, the way to do it.

The Ultimate Car

So, what is the ‘Ultimate’ car? Well, surprisingly it’s fairly easy to define, on paper at least, because technology is driven by desire. Our desire to go faster means that the machines performance will ultimately be limited, not by technology, but by what us humans can cope with. We already have 1000 bhp road cars, and drag racers are running over 8000bhp and doing 0-100 mph in 0.3 of a second, so soon there will be more power available than you could ever cope with.

Looking deep into my industrial strength yet slightly dented and oily crystal ball 70 years ahead into the year 2079, where very little of today’s way of life will exist; All cars have a fully automatic robot driver mode and most countries have put a ban on people driving cars themselves. This may sound extreme but in a world where there is no road rage, no speeding and no tragic lapses of concentration all those thousand of lives that are annually lost are now saved, plus with more economical driving, and electronically interlinked vehicles negating the need for delays at traffic lights the efficiency and emissions gains are utterly compelling. But for a special one off article we find our fictional road tester, Figaro Flashbgure – the only person left who knows how to drive, has just been given permission to drive the latest supercar from the last independent car manufacturer in the world (naturally this will be Morgan) on the last road in the world where you are allowed to drive manually (naturally this will be the Isle of Man).

As Figaro approaches the car it recognises him, the aperture opens and the seat swings out of the car and is presented to him – as he sits down the seat and aperture slide back into place, leaving no evidence of shut lines, and the seat gently folds around him.

Inside the cabin there are two hand grips, but they are just to hold on to much like on a roller coaster, there are no visible instruments or controls. Instead the car transmits options directly into his brain, which appear as if on an inbuilt head up display. This is the same technology most people will have so they can seamlessly play their music, watch films, surf the web and be part of a totally connected world. Figaro selects the ‘lets just go for a drive’ fully automatic option and the car sets off, with a computer generated soundtrack specifically calculated to set Figaro’s senses tingling.

Turning out into the road, the windscreen dims a little to prevent glare, our man selects the old TT route and sets the desired speed as ‘as fast as possible’, which is a balance of what is physically possible and safety limits, so through the historic narrow town streets turns out to be well below 20 mph.

But once out in the hills, the car detects that there is no traffic for miles, linked into all the roadside cameras it can see round bends and see there are no dangers, and then gives it the absolute maximum attack, the total traction system delivers over 10000 bhp sling-shotting the car with a force that nearly causes Figaro to black out, as nausea builds and is detected, the car mercifully eases off. The first corner leaps into view at terrifying speed, seemingly too late the system slashes 100 mph off the speed and throws our man harshly forward, thankfully the adaptive seat firmly holds him.

The car plunges into the corner, still blindingly fast, and the seat adapts again as he is thrust hard against the side, the car calculates the maximum force he can take whilst balancing the force delivery to push the car round the corner in perfect control. The corner has come and gone in a fraction of a second, leaving no time for his brain to come to terms with it all.

The scenery is blurred by the mixture of speeds well above 300 mph and the effect the G forces are having on his brain, looking through the windscreen is like watching a film of the TT race on fast forward. Soon our man has had enough and selects cruise mode, the speed tumbles and the seat releases its vice like grip, peace is restored and the car wafts effortlessly back into town.

After a brief stop at the café to recover, its time to head out again and sample ‘manual’ mode. He settles in and the car gives him a cursor which he simply places on the road indicating roughly where he wants to go, placing it close to the front of the car makes it over sensitive and twitchy, constantly reacting to his small inputs, but placing the cursor further up ahead allows the car to work out the best way of getting there and things smooth out.

He now controls the speed, and as a hump back bridge looms our man really goes for it. The compression as the car goes up pushes him down very hard, the seat grips his legs to force blood up to his brain, much like present day fighter pilots G suits. At the crest, the car pulls strong negative G, flinging Figaro upwards and his stomach threatens to come out of his mouth.

A corner allows him to see how much braking force he can cope with before powering out riding a tidal wave of thrust, sending him dizzy.

After a few minutes of high speed body abuse, our man is badly fatigued from the high G forces sheer concentration. So once again he selects cruise mode, and nearly passes out with relief as calm is restored, and the ultimate test drive comes to an end.

So there will never be a car with higher performance, not until there are better humans who can take higher G forces. Truly the Ultimate car.

 

Is this just some tripe I made up? Well, obviously yes, but it’s all based on sound engineering principals. Here are a few examples of current research to spark the imagination:

Seat adapts to support the driver when generating huge G forces, left, right, braking and acceleration, before reverting to comfort mode when cruising.

(Ref; Lear corp active seating)

Windscreen adapts to lighting conditions, hydrophobic materials disperse dirt and rain so there is no need for wipers.

(Ref; Pilkington SAE paper on hydrophobic glass)

Bodywork is adaptive, adjusting its shape to provide best economy, highest speed, highest downforce depending on conditions. The microbial polymer can heal small scratches and dents automatically.

(Ref; Lotus SAE Paper on adaptive bodywork)

Mind control does away with the need for controls and instruments, making the cabin more spacious and safer. Just looking at where you want to go tells the car where to steer. Most people in this year have tiny implants to connect to the internet, sound systems and most domestic devices. But even without that, Honda have already demonstrated an electric wheel chair controlled by thought.

(Ref; Sony report on thought controlled games, also Prof at Reading uni who plugged his head into the internet, Honda mind controlled chair)

Wheels are still hard to beat, but these tyres are based on the same principle that Geckos use to cling on to walls, covered in microscopic hairs they look fuzzy, slightly flat and never wear down. They bind with the road surface allowing negative G over hump back bridges. Info from the hair sensors feeds back to the computer telling how the road surface ‘feels’ and precisely how much grip is available.

(Ref; 3M report on interference layer adhesives, Michelin SAE paper on active tyres)

Active suspension allows the computer to simulate any desired handling characteristic, if you want it to feel like an Allegro then just select the option for a nostalgia trip, or select max to explore the limits of physics.

(Ref; Lotus report on active suspension)

To generate over 5G of acceleration the electric powertrain is capable of delivering well over 10000 bhp. Each wheel is a motor, delivering total control of power delivery to each wheel for the maximum traction physically possible. Biasing the torque left and right delivers power steering effect and yaw control.

(Ref; Bosch paper on torque biasing and traction optimisation, Michelin wheel motor)

Fuel is a thing of the past, the battery is also the vehicle structure, providing strength as well as power, and this combined with the wheel motors means that all the space in the car is available for occupants or luggage, no engines, radiators, drive shafts or gearboxes cluttering up the space.

(Ref: Carbon NanoTubes used as a battery and structural composite)

The outer body also acts as a solar cell generating all of the car’s normal requirement of energy.

(ref: Pyradian ‘solar electric’ film from NLV Solar, Koenigsegg Quant)

Brake discs are a thing of the past, the motors can haul the car to a perfectly controlled stop as quickly as the tyres and road can allow. Back in our present day drag racers suffer from the hard deceleration of deploying parachutes at over 300mph, some suffering from retinas detaching, but our car of the future doesn’t brake quite that hard in order to save our man’s eyes.

(Ref: Regenerative braking)

Steering is on all four wheels and adjusts for stability at high speed and manoeuvrability at low speeds, when parking it can crab sideways. Torque biasing on each wheel gives power steering effect and high degree of yaw control. Running wheels on one side backwards when parking allows the car to turn on the spot.

(Ref; Honda report on AWS)

Sound is an integral part of a thrilling drive, a screaming race engine can spur you on to drive faster, and a gentle wafting luxury motor can sooth you into driving more gently. As the drive motors make very little noise, a computer generates a synthesised soundtrack to suit the mood. Sound is also broadcast outside to alert pedestrians and animals to the oncoming car.

(Ref: Lotus active sound)

Instead of an accelerator pedal he can simply will the car to go at any speed, but the car will still not enter a corner too fast or pile into oncoming traffic and so gives a safe operational envelope within which to play and explore the cars awesome capability.

The car communicates with other traffic and mingles effortlessly in total safety, if a kid runs out in front of a car up ahead the whole line of cars slows in unison, preserving safe distances. Ground penetrating radar and other sensors detect the road surface ahead, so the car is constantly ‘aware’ of all the potential dangers around it.

(Ref; DARPA test reports)

This article was originally written in 2000, then updated for Evo in ’09, and finally taken from the fridge and reheated for this blog ’10.

The beginners guide to exhausts

The pipe the takes the exhaust gas away from the engine and lets them loose at the back of the car so the occupants don’t breath it in. Normally it has mufflers (silencers) to reduce the very high sound levels that the engine produces, without some sound reduction the cars occupants would end up deaf very quickly.

Usually the exhaust comes in several parts, the bit attached to the engine is the ‘Manifold’, this is connected to the ‘System’ which goes all the way under the car to the back. The system starts with the ‘Down pipe’ coming from the manifold down under the front bulkhead, then there may be a front section with catalysts, a mid section with a larger silencer and possibly a separate rear section with a smaller silencer and finishing with a ‘Tail pipe’ showing at the back, although there are many other arrangements too.

As well as transporting the waste gasses safely away and muffling the noise down to acceptable levels, the exhaust also effects the engine performance, its has to be big enough so the flow is not restricted. But also the gas speed needs to be preserved for high speed power, so making the exhaust to big can actually reduce power. As with all tuning its a fine balance to get the best performance, and there is no one perfect solution.

The bit that bolts to the engine is the Manifold, it has a tube for each one of the cylinders which join together. The exact way they join together and the length of the tubes makes a big difference to the tune of the engine, they can improve low end torque or sacrifice that for peak power. Its important to get the shape and size of the manifold ports to match up with the exhaust ports on the engine, any mismatch can restrict area or leave a step which causes turbulence and reduces flow.

There are two main types of muffler, one uses absorptive rock wool matting and the other type sends the exhaust gases through a sort of maze which breaks up the sound pulses. Generally the absorptive type removes high frequencies and the labyrinth type removes the basey boomy noises.

Most standard systems have a mixture of both, but for a more sporty sound they can be replaced with simpler ones that have less noise reduction and slightly more flow.

Twin pipes are still popular, factory fitted to most V engines which have two exhaust manifolds, they run an exhaust pipe on each side of the car floor pan and finish with two tail pipes.

On V6 and V12 engines these can be two totally separates systems, but on V8 engines they often have a balance pipe between the two systems close to the engine in order to run smoothly because of the way the firing order overlaps, giving an uneven sequence of exhaust pulses on each bank and that distinctive burble.

The least important part for performance is the tail pipe, usually finished of with a decorative trim.

Many systems run twin tail pipes running from the back muffler, although some systems try to get the twin pipe look by fitting a Y piece close to the back.

Catalysts (cats) convert partially burnt fuel and fumes into carbon dioxide, water and nitrogen. They do this by passing the exhaust gas over an immense area coated with an incredibly small layer of precious metals such as platinum which do the actual catalysing bit.

And it really does need a huge surface area to work, this is archived by folding the surface into a honey comb and by giving it a microscopically rough surface. In fact a typical catalyst can have the same surface area as a football pitch, all folded up into something the size of a 3 litre pop bottle, amazing.

It only works when its hot, at least 300C and preferably 600C, so it is usually put as close to the engine as possible so as not to loose any heat. In order for it to heat up quickly cats are usually made of ceramic which makes them fragile, so the catalyst brick is supported in the can by a soft fibre mat.

So if the cats hit a bump in the road there is a fair chance they will shatter. Also if the engine is tuned badly then un-burnt fuel will burn on the cat face and melt it.

When cats were first fitted back in the ’70s they were too small for the job and would restrict flow, modern cats are usually very good at flowing and can even cope with mild tuning, but for big power gains usually a bigger sports cat is needed. Racing cats use a metal brick instead of fragile ceramic, it takes longer to warm up but can take more abuse.

Exhaust systems can be either mild steel that has been coated in an aluminium based protective layer making it look dull silver, or made of stainless steel which lasts much longer and looks shinier. Stainless is a harder metal and so when it vibrates it makes a higher pitched noise, some people claim stainless exhausts sound ‘tinnier’ than mild steel ones.

The difference between quality brands and budget options is often in the grade of metal, cheap stainless will start to rot nearly as fast as quality mild steel. Also cheaper systems can end up with rusty welds, mild steel systems should have been coated after welding and stainless systems should be welded with stainless wire, not the cheaper mild wire. If the welds on a new system look rusty then it was a cheap one.

Sound affects our mood and generates strong feelings, so the exhaust sets the tone for the whole car. Get it right and the car sounds strong and purposeful, get it wrong and it sounds like a fart in a tin can.



Things you might not know about tyres.

As ever rubber-ware is critical, the rubber compounds are carefully engineered with a range of other substances such as carbon powder and silicon and then heat treated to give it just the right properties. There is a hell of a lot of technology in that black stuff.

The tread pastern is designed with channels that pump water out of the contact patch area at an amazing rate, for instance an F1 rain tyre can pump out 80 liters per second, but the tread does a lot more than that. The flexibility of the tread blocks allows them to move and adapt to the road surface to find grip, winter tyres have lots of small deep blocks of soft rubber with extra tiny groves in them so they can even get some grip on ice. A lot of people in the UK don’t realise there are different tyres for summer and winter use, but in many countries swapping to winter tyres when the cold weather starts is compulsory.

Winter tyres don’t work so well in summer, at speed the narrow tread blocks wobble about and overheat which looses grip, so summer tyres have wider tread blocks with a shallower tread depth. Track day tyres go a step further and have fewer grooves and some of the tread blocks go right the way round the tyre.

The tread compound actually wraps round the microscopic lumps and bumps in the road surface to give grip. At speed the rubber molecules have to grab hold of the road then let go very quickly, softer rubber reacts faster and flows deeper into the road irregularities giving more grip but gets ripped apart more easily when it has to let go, so soft tyres wear faster.

Full on racing slicks have no grooves at all to maximise the contact area and reduce overheating. It still has a tread layer because the rubber compound that contacts the road is much softer than the rubber compound used the make the structure of the tyre.

The side walls have to be stiff enough to keep the tread section under control and the base layer under the tread layer needs to be strong enough to hold the tread securely and resist punctures. They are reinforced with cords of steel or Kevlar, the precise weave effects how the tyre deforms on the road and so effects handling. Generally track tyres are more supple but wear out faster and with only one or two plies are more prone to damage, by contrast tyres built for vans and trucks are harder with many more plies making them last much longer and resist damage at the expense of ultimate grip.

Stiffer or lower profile sidewalls give a quicker change of direction, but can’t follow rougher roads so easily and may skitter a bit, that’s why race cars don’t often use ultra low profile tyres. A taller and more flexible sidewall is better on poor quality back roads, but it also introduces a small delay making it feel slow to turn in and a bit vague.

A wide wheel holding a narrow tyre holds it very rigidly, which is great for flat smooth race tracks but stops the tyre adapting to rougher road surfaces. By contrast a narrow wheel on a wide tyre allows the tyre to move side to side and curling up at the side when cornering hard making the handling a bit sloppy. Excessively wide wheels in narrow tyres may allow the bead to be pulled off the rim, which is bad.

Changing the tyre pressure can transform a car’s handling. Lower pressures allow more flexibility but too low and the tyre looses control which is very dangerous. Higher pressures hold the tyre more rigidly, to high and it can’t react well and the handling becomes a bit wooden. The best grip level is somewhere in the middle, and it varies depending on the intended use of the car, a little lower for a comfy ride in a road car and a little higher if the same car is on a race track.

Tyres age, the first visible signs are tiny hair line cracks in the base of the tread blocks which means its past its best and in no use for performance driving, but it also perishes from the inside so old tyres should be avoided, 3 years for a track tyre and 6 years max for a road tyre is the norm. The tread rubber gets harder over time as it ages and also because it gets hot in use which reverses the heat treating process it was made with.

On a race car when the tread overheats the grip disappears very suddenly, this is called ‘going off’. If road tyres are required by the regulations the tread is cut down to about 3mm depth to minimise the heat generated by the tread blocks wobbling about. New race tyres are run through a gentle warm up and cool down first to settle the compound molecular structure, going straight out at full tilt on new tyres ruins them.

The tyre is the only thing that connects the car to the road, everything that the engine and suspension does ends up as a single simple force on each tyre’s tiny contact patch. Tyres effect the cars performance and handling more than any other single component, and its not just a case of bad tyres vs good ones, but its about choosing the right type for your car’s purpose.

Cold Shoulder



As engineers we have to test cars in all environments, and whilst a lot of time is spent testing in hot and cold countries the bulk of testing is done back at the engineering centre in special climatic chambers. These are basically glorified garages with a high powered air conditioning systems that can chill the cars down to -40C or heat them up to 50C.

I have to say that -40 is very chilly, but some weird things happen when testing in a chamber. For a start there is no wind, so as soon as you walk in from the nice warm office you don’t feel the cold, not straight away anyway, it sort of creeps up on you and can catch the unwary out leading to sudden loss of blood pressure and blacking out. This results in the strange phenomena of seeing engineers wearing full Arctic clothing in the office in the middle of the summer, often with frost on.

There are a few crucial rules to observe when getting into a chilled car, everything looks normal, the car has no frost on because there is no moisture in the cell, it just looks like a normal shiny new car. Those publicity photos of cars covered in frost are made by spraying water from a plant sprayer over the car first, who ever said the camera never lies!

But even though the car looks normal if you touch a metal part with a bare hand the moisture in your skin will instantly freeze solidly to the metal part, pulling away will rip the outer layer of skin off but staying put will gradually freeze the whole hand, this is to be avoided.

The reason moisture is not present is that at these low temperatures it simply falls out of the air, which is handy as any dampness in the door seals would freeze and lock them up solidly. The test chamber has electrically heated door seal for precisely this reason. I once made the mistake of driving a car into a chamber after it had been raining, many years ago, by the time the car was cold enough to test we couldn’t get the doors open, eventually three crowbars, a dented door and torn door seal later we could start work.

Strange things happen when you take a frozen car out of the chamber, particularly on a typical wet British summers day when there is a lot of humidity in the air. As soon as the chamber doors are opened the warm humid air rushes in and turns to fog, instantly obscuring the frozen windscreen.

As you drive the car out it works as normal, then moisture freezes on the tyres which are still well below zero, they make a crunching sound as the car rolls forward and can skid if the road is wet. Its strange but for a few yards until the tread warms up its like driving on ice, but on a warm day.

The next trick catches many people out, when first moving the car out of the cell the brakes work normally, but as you drive across the yard ice forms a hard layer on the discs and as you park up the brakes don’t work. By which I mean they don’t work at all, the callipers are squeezing on smooth ice and there is no retardation at all, not even the hand brake works. The trick is to drive with the brakes on until the discs have warmed up to zero.

Proper climatic chambers cost a fortune and are always in short supply, so some companies use cheaper options. I once worked for a well known gearbox manufacturer who used a modified artic freezer trailer that used to take frozen fish to the shops. It was just possible to get a car in and open the drivers door enough to get out, but it was tight. The control didn’t have a thermostat, just a lever that ran the chiller to a greater or lesser degree, there was one engineer who had got the feel for how far to push the lever to get the desired temperature. Usually he got it bang on, but not always.

On one occasion I loaded a prototype car in and he set the control to give us -20 for the following mornings cold start test. Or so he thought. But overnight the ambient temperature dropped unexpectedly quickly and instead of -20 we got something nearer -40, a temperature where the engine had yet to be calibrated and stood no chance of starting at. The only solution was for me to attach a large truck battery (the cold oil was to much load for the car battery) and apply a hot air gun to the intake until it stood a chance of starting. Remarkably this bodge worked and the prototype engine spluttered into a very lumpy idle. It was then that I found my thick soled shoes had frozen to the floor! It was a few more minutes with the hot air gun before I could escape.

Such is the glamorous life of an engineer.

How many cars can an ‘Enthusiast’ have?

Or put another way how much space do you really need…

Phenomena from the parallel world of project vehicles.
Indeed, fleet size is related to theoretical storage places thus:
Fs = Pth + Ptemp + int(0.5+(Dnew + S))
Where
Pth is the theoretical storage places is based on Mini sized vehicles, stacked.
Ptemp is theoretical storage places available on a temporary basis from friends and family,
Dnew is variable between 0 and 1 based on desirability ratio of the new purchase.
S is the imaginary factor, 0 to 1, induced by the concept that ‘its a scrapper with loads of good bits on which I can sell on eBay and make…’

Thus, someone with only one parking space will own two cars and be in the process of scrapping a third, in a friends chicken shed, whilst looking at prices of an intermittent fourth.
There is also the fact that when four or more actual spaces are available, one of the vehicles becomes a ‘long term project’ and will not move for at least five years until trees grow through it, only then may it be replaced with a newer long termer.

Garage capacity.
Garages are permitted to only store half their actual storage capacity (as opposed to theoretical capacity which is based on packing cars in so tight you get out through the sun roof and lift a mini in sideways).
The other half must be full of the ‘useful bits’ that you took of the scrappers over the last decade, plus half a bag of soil per car per year stored.
There is also the ‘cyclic focus phenomena’.
This is where one starts with a wreck (project) and one purchases another wreck (donor) in order to restore the first wreck to its (imaginary) former glory.
At the start of the process wreck A is the focus of all the attention. Talk in the pub centres around original or novel features and the fact that one much like this almost won le Mans in 1963 (but with a different engine and chassis/body). Mention is also made to the massive potential the car has to be ‘tuned up’ to produce five million hoarse power by using the Canadian market intake and tubular exhausts.
Wreck A was bought with a few months MOT left on it. It was driven round a bit and only broke down when it rained or after it was left parked on a slight incline. Then it was laid up in an arbitrary garage/lock up/friends field with a tarp over it (thus ensuring massive corrosion).
This must be left for at least six months before any work may start. Don’t know why but it just seems to be that way.
Then, one day when the sun comes out, an investigation reveals corrosion (we can patch that up), some parts completely worn out and some bodges that the previous owner has installed. How it got an MOT like that is a mystery, but you would quite like to know the number of that garage to see if they can do your other cars!
So many parts are needed that wreck B is purchased.
Wreck B is a bargain, it has almost (but not quite) all the bits you need plus a really ‘desirable’ dash quadrant trim piece that you are sure will sell on ebay for the price of the car.
Whilst removing the seats, you see shiny paint and notice the floor is in really good condition, much better than wreck A.
There now follows the ‘focus re-alignment phase’.

A gradual process where more parts from wreck B are to be fitted to wreck A, until the tipping point is reached and there is more of wreck B in Wreck A than there is original bits.
There now follows much discussion and beer drinking. Some standing around the car and a fair bit of pointing at it.
Now the plan is to fit a few bits from A onto B and swap the registration.
During this whole phase, no actual parts are physically touched, they just sit there, rusting and seizing.
Now the focus has been successfully moved to wreck B and wreck A will be sold as a ‘project vehicle, 90% finished’.
Money has been spent, rent has been paid, time has passed. But you still have a shit car.

Abnormal behaviour.
Anyone found with space in their garage will be excommunicated immediately. Anyone found with a clean and tidy garage will be shot. Anyone thinking of converting a garage into a spare room will be shot twice and excommunicated an indeterminate number of times.