Why fit another exhaust to my vehicle?by Richard Dobson
GMC Motorsport
www.gmcmotorsport.co.uk
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 kit exhaust 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 exhaust system because the old one is worn out is arguably the best reason, as many performance exhaust systems are not that much dearer than the manufacturers replacement and on some models even cheaper. Do not compare a non genuine replacement exhaust from your local free fit garage prices with manufacturers own or performance exhaust 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 a non genuine exhaust system, we fitted the rear silencer to a customer's car, 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 exhaust 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 performance exhausts are more powerful but on the dyno the results say the standard exhaust 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 freeflow 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 exhaust back pressure, which builds up and pressurizes 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 an exhaust system with a much bigger bore exhaust pipe all the way from the front to the exit, the size being 63 mm. (Photo: BTB Pipe Diameter In Comparison To A Standard VTS System) | 
