2.5" exhaust vs 2.25 or even 2"

It's not so much the size of the pipe as much as the type of equipment used to make the bends. Crimp bent exhaust is the worst. Shop bent is a little better. Mandrel bent makes a tremendous difference in flow as the flowpath literally stays 2.5" the entire time. On several cars in the 400hp range, our tests revealed a dyno difference of close to 50hp over a decent shop built 2 1/4" and a 2.5" mandrel bent system. Real world results; A Yenko Nova running 14.6 in the quarter mile with shop bent exhaust switching to Pypes 2.5" mandrel bent exhaust and no other changes. 14.1 That .5 of a second. For those that race, you know that is huge.

Since there it is very rare to see mandrel bent 2 1/4", 2 1/2" is a great solution and only hurts a little on the bottom end. Since most rebuilds have loads of bottom end torque, 2.5" is the most efficient and cost effective solution for someone that wants to maximize performance at a very reasonable cost.