Professional Answer to Exhaust Size Question 2.5" vs 3"

There is a lot more to do with the size of the pipe than the HP of the engine. Camshaft plays a critical role in designing an exhaust system. An engine with a high overlap camshaft can not use a small exhaust system as it will be overscavenged. To say it plainly if you got a big cam in it use the 3" pipes. If you have a small cam use the 2 1/2" pipes. There is much more to exhaust then production header manufacturers know about as the dont build real high end systems. I only build high race headers, and all my work is designed for each combination. PM me the overlap of your camshaft, if you dont have that give me the lobe seperation and and the duration at .050 and I can give you an educated guess at what size exhaust pipes to use.

Mark Lelchook
Performance Welding
Racing Headers