I would say that a good exhaust system couldn't make your engine produce more power as a straight piece of pipe can make your engine work properly, but a system that is unsuitable will cripple it. A well-designed system is made to reduce noise without losing power. The exhaust manifold is the most important part of the exhaust system, but it will only work properly if the system it is connected to is of a good design, e.g. unrestricted and of the same diameter as the exhaust manifold chosen. If it is not it will reduce the efficiency of the manifold. In some cases we may recommend a system of a larger diameter.

The exhaust manifold is one of the most important parts that control the output of an engine. You can spend endless amounts of money on tuning your engine internally, but if the exhaust manifold's design does not complement it, your engine may not produce the power you expect. It may move the torque band into a different place, causing all sorts of problems. For example if the manifold you have chosen to fit on your engine is designed to give an all round mild improvement over the standard item, it would be useless to fit it to a full race engine. A full race engine would be strangled & as the engine begins to come on cam at quite high RPM, the exhaust gases would be totally restricted & probably generate nothing like the power expected. If your engine has been designed to produce large amounts of torque at low RPM for a particular type of motor sport, e.g. National Hotrods or Grass track racing. If you were to fit a full race exhaust manifold it would not help the engine at lower revs to produce its full potential, since the manifold is more suited to higher rpm.

We have done extensive testing with 16v Vauxhall range of engines, spending hundreds of hours testing manifold designs on the dynamometer & just by changing the diameter of manifold pipes as little as a 1/16", or its length by only ½", you can get quite dramatic changes in the characteristics of an engine. If the manifold you have chosen to use is badly made, or of the wrong design, the problems you will experience will increase as you tune your engine further as time goes by. This is because when the engine is only mildly tuned, although the exhaust manifold is still important with mild cams fitted, the manifold is called upon less to help with the charge of fuel rich air being drawn in to the engine on the overlap. Overlap is when the exhaust cam is about to close and the inlet cam is just opening. But as the engine is tuned further the amount of overlap is usually increased. As this happens the manifold then becomes more important because it is used more & more to help with the incoming air fuel charge which the engine needs to generate power. If its design does not match the characteristics for which the engine has been designed, the manifold could be at its most efficient at the wrong RPM and have past its optimum when the cams begin to start working. Or maybe the complete opposite, the exhaust manifold may not be at its best until the cams have past the working rev range.

In the case of a fuel injection engine, if the manifold you choose to run is not to the same spec that it was originally programmed on and is totally different in its design, not only could it stop your engine from producing the power, it is likely to change the fuel requirements of your engine. So it could even it by under or over fuelling unless it is reprogrammed to suit

Frequently asked question about exhaust manifolds

But if you decide to ignore any of the above don't come running to us saying that your engine doesn't produce the power we promised. Since we only know what power your engine should produce when it has been built carefully with the correctly matched and accurately made exhaust manifold and good quality exhaust system.

There are two basic types of exhaust manifolds the 4>1 and 4>2>1. The 4>1 manifold is traditionally used on an out & out racing engine. This is because they work well at higher RPM but they are not very good at low of mid range RPM. The 4>2>1 manifold normally works better in the lower & mid range RPM areas but is not as good at higher RPM. We have developed a range of exhaust manifolds combining the best characteristics of both these types of manifolds, which involves using unusual length primary & secondary pipes. We would recommend a custom made exhaust box be made for your car, since the box specifications will depend on your requirements as regard to use & noise limitations. BTB Exhausts would be happy to discuss your requirements

Please choose the type of exhaust manifold most suitable for the output of your engine.