Exhaust H.P.

2007Mazda3i

I've put a 2.5 inch exhaust on my 2007 Mazda 3i . That includes the resonator, muffler and the exhaust pipes from the cats back. Can any one give me an idea of how much h. p. I could get from this mod ?

thecardoc3

Little if any. It's not just about being bigger, it's about being tuned so that the inertia of the exhaust gas pulses comes into play and helps pull air from the intake manifold during valve overlap. Scavenging of the gasses in the cylinder is an important part of building the header the exact correct size and then porting them so that they create some vacuum for the next cylinders pressure pulse. Exhaust that is bigger than it needs to be causes weaker scavenging and that means there is less room in the cylinder for the next intake charge.