decat - increase/decrease performance?

[quez]

hi, i've got a kitted up mk1 1.4rt with a cat back 2 x 4" slash cut s/s exhaust system. i've been told by the guy who made the system that a decat would only decrease my performance, is this true or should I get 1?

 

[BRUN]

thats balls, they DO increase performance, especially top end

pm Lunner he will sort you out with one

 

[thedoc]

the back box could lose you power, all to do with back pressure.. but cant see a decat losing you power.

all here..
Performance exhaust systems are designed to increase the ability of these exhaust systems to flow a larger volume of air with less restrictions. A less restrictive exhaust system will generally result in more power up to the point at which there is enough back pressure to allow the vehicle to run properly. Back pressure is a measure of how restricting the exhaust system is to the used exhaust gases moving backwards in the exhaust pipes towards the engine. If an exhaust system does not provide enough back pressure, the engine may actually pull used exhaust gas in through the exhaust valve while it is still open during the beginning of the intake stroke. This would contaminate the fresh air-fuel mixture entering the combustion chamber and reduce the power generated by combustion. The point is, that there are limits to how large a performance exhaust system can be, before the "performance exhaust system" will actually start to rob horsepower (not to mention creating running problems).

 

[theduck]

depends on the system, and the decat u get. in its possible that with too large a bore and a straight through decat, that you would have problems. if the system is right for the car in the 1st place a decat will only make the system less restrictive and increase performance.

which is what that says ^^ lol, should have read it Before posting