Professional Answer to Exhaust Size Question 2.5" vs 3"

perfweld said
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

Here it is and Thanks much!
Cam StyleMechanical roller tappetBasic Operating RPM Range2,500-6,500Intake Duration at 050 inch Lift242Exhaust Duration at 050 inch Lift248Duration at 050 inch Lift242 int./248 exh.Advertised Intake Duration280Advertised Exhaust Duration286Advertised Duration280 int./286 exh.Intake Valve Lift with Factory Rocker Arm Ratio0.570 in.Exhaust Valve Lift with Factory Rocker Arm Ratio0.576 in.Valve Lift with Factory Rocker Arm Ratio0.570 int./0.576 exh.Lobe Separation (degrees)110Intake Valve Lash0.016 in.Exhaust Valve Lash0.018 in.Computer-Controlled CompatibleNoGrind NumberCRS XR280R-10