they only make a difference on HIGH horsepower cars that make big power at the top and don't need the backpressure. People who do them on mildly modified cars don't really know why they do it... its coz their friends mums brothers dogs girlfriends auntys sons moms sister said its t3h h3ktic1!111!!!!Originally Posted by absolutR
heres simple proof, on a bogstock B16a2, get a full 2.5in mandrel bent exhaust, you will notice a loss in low-mid range power and response for a MARGINAL gain in topend.....
a very effective high flow cat will actually give gains because:
- the catalyst is more effective while flowing more therefore...
- apart from burning like blow-by oil that went in the combustion chamber...
- it effectively ignites any unburnt fuel mixture also which may cause exhaust pop...
- and because exhaust cools down as soon as it leaves the head, the catalyst re-igniting them creates heat and accelerates exhaust velocity again, therefore...
- 'scavenging effect' is increased as increased exhaust velocity creates vacuum and pulls gases from the combustion chamber when the exhaust valves open, therefore...
- also scavenging more air on the intake side come the time the intake valves open....
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