540rwhp (630 HP flywheel, 844 CFM) according to the not2fast.com calculators will require 3" IC piping... 470rwhp (740 CFM, 550 HP flywheel) is the upper limit for 2.75". From 470rwhp-540rwhp, 3.0", from 540rwhp to 660rwhp, 3.25". That's with assloads of assumption, such as a constant 15% drivetrain loss, assuming that this calculator has a correct CFM to HP ratio, etc. etc.
