yeah guys, it's really quite simple. I said this a while back, but for those who weren't on the board b4....
A smaller exhaust will make more torque, while a larger exhaust will make more horsepower.
On mine, I decided to run 2 1/4's on some super comp's, because I didn't want to lose the low end grunt that I need to move my 39's. With the resistence to air comparable to a brick, I suggest that you don't run anything bigger than a 2 1/2, or you're gonna be winding it for power, and quite possibly have some sick sounding back pressure.