Originally Posted by swartlkk

Backpressure being required for an engine to operate properly is a myth. There can never be too little back pressure. There is such a thing as an exhaust that is too large however. Basically, you want the exhaust sized appropriately such that the scavenging effects are maximized. Scavenging is when one exhaust pulse pulls along the next as they travel through the exhaust pipes. Too large of an exhaust and the pulses slow down too much when they expand in the large tube and do not have enough momentum to aid the next pulse. This is what happens when people throw on a large exhaust and loose low end torque.

Unless you have done things to shift the power or torque higher in the RPM, you don't need anything larger than a 2.5 through out. The reason why the factory pipe necks down after the muffler is because of how much the exhaust gasses have shrunk due to cooling. Going 2.5" all the way will improve the top end without changing the low end.

Originally Posted by Dolanjohn1990 (Post 498207)

That wont cause any backpressure issues or anything with my rebuilt engine will it? Im hoping to send it to the shop this week and yours sounds, well, badass