Well for the old motors (B and H series), the biggest piping I've seen people run on the streets is 2.5 inches, and that's with bigger cams and raised compression. With only minor boltons, no bigger than 2.25. But now I see K series powered cars running 2.5 inches with only minor boltons (i/h/e)! Doesn't the low end suffer alot with that big of a piping? So what size exhaust piping should I run? I plan to go all the way with the motor, and have it stay a daily driver(run on 93 gas), still deciding between what CR I wanna upgrade to later on: 11.5:1, 12:1, or 12.5:1. This is a TSX motor by the way.