Exhaust Systems

We are stockist of  Piper and Peugeot competition exhausts, plus we have our own design BTB 4-1 exhaust manifolds for TU engines. We have also has a special exhaust system made for our supercharged cars, this unit still fits any Saxo or 106. 

Why fit another exhaust to my vehicle? There are several reasons, style, performance, sound and "the old one needs replacing". Style cannot be argued against as most standard system's exit through a boring small, often rusty tail pipe. Performance is a harder one to equate, as putting a performance big bore system on a standard engine is unlikely to produce much benefit. Sound is hard to give an opinion on, and one person’s noise is another’s music.

Changing to a performance system because the old one is worn out is arguably the best reason, as many performance systems are not that much dearer than the manufacturers replacement and on some models even cheaper. Do not compare non-genuine replacement exhausts from your local free fit garage prices with manufacturers own or performance systems, as not only are the majority made out of thinner or lower grade material but from our experience reduce performance. Most performance exhausts, including Scorpion, Piper, Magnex and Musketier are made out of stainless steel, which is superior in every respect, especially against corrosion, which is the main killer of exhausts, so when comparing prices and value for money make sure you are comparing like with like.

To give you an example of non-genuine systems, we fitted the rear silencer to a customer’s vehicle, he insisted on none genuine to save money. At the same time we carried out a full service and a day after he was back complaining we had done a bad service, as the car was sluggish at high throttle openings. We rechecked everything and every thing was ok, so in desperation we fitted a genuine rear box, performance restored.

A few more words are needed regarding the Piper and BTB systems. We like the Piper units as they are equal to all the others as regards performance but the big benefit is that you can get about 6 different tail pipe designs, round, oval, twin , slashed etc etc.

The BTB Unit

As said above the majority of so called performance exhausts will not increase performance, especially on a standard or near standard car, sure they look good and maybe make a lot of noise, that makes you think they are more powerful but on the dyno the results say the standard unit is very good. It is only when you start to make a lot more power that the exhaust system needs to be changed for a true free flow unit, due to fact you are burning more fuel and so have a lot more exhaust gas to get rid of. We found this a particular problem on our supercharged cars, the power would go up and then level off as the exhaust just could not pass the gas, causing back pressure, which builds up and pressurises the exhaust ports and so stops the gas coming out of the cylinder, this in turn means the cylinder does not get rid of all the burnt gas and so contaminates the new charge stopping it burning as it should and so reducing power. We found that for every 1 lb of boost there was 1 lb of exhaust back pressure. The solution was to make a system with a much bigger bore pipe all the way from the front to the exit, the size being 63 mm.

A case that proves this point is we had a supercharged Saxo VTR in our workshops, it was a car that had had our kit fitted by another garage. After correcting numerous other faults we dyno tested it and it went to 130 bhp at the wheels and just stayed there from 5000 rpm to the rev limiter. We took off the "performance" system and fitted the BTB unit, 150 bhp without any other alterations. I know many of you may say, "Well I do not need one of these my car is not supercharged". Yes, I would agree up to a certain point. This problem is not because it is supercharged but because the engine is producing a lot of power and hence a lot of exhaust gas, this same problem will come about with a normally aspirated engine if the power level is increased a lot. We have done no tests, so have no figures to say at what level of BHP this back pressure problem will start but I would guess at anything over 30 BHP increase and the bigger the BHP the more of a problem. It is something worth considering when you have just bought your car, as many start off by fitting a new exhaust as the first job. What you should do is think where your tuning mods are going to stop, as many have plans to fit an air filter, ex manifold, cams, head job etc. If you think your tuning is going down this road get the BTB do not get any other as if you go for big power later it will mean you need to change your exhaust system again.

Another reason to fit the BTB unit is a bit more technical, most people want to take the CAT off as they sap so much power, the problem is taking the CAT out and substituting a straight pipe is not really correct. OK, this will certainly give you the power back the CAT takes away through restriction but this causes another problem. When exhaust gas comes out of the cylinder it produces sound/pressure waves that travel up and down the exhaust system, if these S/P waves can be controlled correctly they can be harnessed to draw extra gas from the cylinder and so make the engine more efficient. These S/P waves are controlled by the cam timing and the pulses go down the exhaust until they meet the first expansion chamber, silencer, CAT (anything that causes the size of the exhaust bore to rise significantly). As soon as the gas reaches this expanded section, the S/P wave stops and goes back to the cylinder head, as this wave hits the back of the valve it bounces back and causes a suction pulse that helps pull more gas out the next time the valve opens. The problem is the distance from the first expanded section to the cylinder head is critical, to get this pulse action working correctly, if this distance is not correct the wave goes back at the wrong time and hits the gas coming out of the valve and so stops the gas coming out rather than helping it. This is what happens when you take the CAT out, you no longer have an expanded section in the correct place and the S/P wave will go down the system until it reaches the first silencer box before returning. Before CAT's were fitted, this was the reason all cars had an expansion boxes in a similar position to where they now fit CAT's. I know some one will say, what about the VTR with the CAT on the down pipe, or the old mini with only one silencer at the rear. The complications of how these S/P waves travel is not quite as simple as above. Lets assume the correct distance from the valve head to the first silencer should be 80 inches, providing you double or treble the distance or half it, quarter it, the S/P waves will still work their effect, so having the CAT on the down pipe or just one silencer at the back can still be right, what is practically certain is that taking the CAT out and substituting a straight pipe will not be correct and so you will loose some power.

The BTB system we make is from the manifold back, with a box put in the place the CAT would normally be (It also looks like you have a CAT fitted if anyone has a casual look) and so keeps the S/P waves correct.

The BTB unit is a more expensive than the others on the market as they are so much bigger, with a lot more stainless steel needed to make them, one benefit is however you do not need to buy a de cat pipe.

Having said all of the above about taking the CAT out is not a perfect solution, it is still better to remove it, than leave it on. The reason the CAT causes the back pressure problem is it does, is it's construction. As said before a good condition car does not need a cat, the reasons for the manufacturers fitting them is that if the car was out of tune and running rich, the gas would be very polluting and so the cat then comes into play. So for most of it's life it is doing nothing, except under cold start conditions. The way the cat works is that the gasses are forced through a honeycomb of small holes that are coated with special metals which form a chemical reaction to purify the gasses. It this forcing the gas through the small holes that creates the back pressure.

Many people ask about the legality of removing the CAT, especially in regards to passing the M.O.T., all the law says is that the gas exiting the tail pipe must conform to a certain standard, any car that is in good condition and regularly serviced will pass the CAT test, with out one fitted, even cars that have been modified quite a lot usually still pass. For those that do not we can provide management to overcome these problems.

One thing concerning a lot of 2001 onwards VTR users is the fact the cat is now on the manifold (VTS still underneath), see the manifold section for info on how to get around this problem.

FULL STAINLESS EXHAUST SYSTEM FOR C2

This system can be had in either 2 inch bore or extra large 2.25 especially for highly modified or boosted cars. Also very shortly a twin exit system will be available.

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