Author: Ralph Hosier

So, what is the ‘Ultimate’ car? Well, surprisingly it’s fairly easy to define, on paper at least, because technology is driven by desire.

Continue reading “The Ultimate Car”

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.

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.

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.

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.