Quote:
Originally Posted by Mitchelkitman
It's all very well altering the boxes for appearance and/or audio, but at what effect to the performance or emissions? Back pressure in an exhaust system can be quite critical, so what effect do the silencer changes have - or is it not really critical (is the cat upstream of all this?)
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We always leave the cat on and build the exhaust from there backwards. It only has an oxygen sensor before the cat with an analogue signal to the ECU. Some vehicles have a post cat sensor to tell the ECU what is happening after the cat which is a digital system. No Z3's have the post cat fitted. Smaller engine cars rely on back pressure which is basically a sound wave which is bounced back by the silencer to help boost the power. However on larger engined cars it is better if there is no back pressure and you are getting rid of the exhaust gases as unrestricted and quick as possible.
Dragsters have unsilenced, short, huge bore (a pidgeon could nest in) exhausts for this reason.