to be honest the power gain from 3" to 4" pipe is minimal. also, anyone with headers has just opened up the exhaust so much that it will never be a restriction again. hell, these cars do great with just a 3" downpipe. once the exhaust is opened up the next place is the intake. once the intake is opened up the next thing is the valvetrain. the stock cam and rockers can only move so much air. with higher ratio rockers or a cam with more lift, the car is able to move more air.
most people never get as far as wanting a cam in their car, but some do. id say once your intercooled or are running a cam its time to go open cone anyway. this negates all tubing anyway. so i guess what im getting at here is that you can run whatever you want, but you sure as hell want it to be bigger than the throttle body inlet, which is 3.5". my reasoning isnt so much about needing a bigger intake, its about the want for it and the room to grow from there.
also, dont be a smart ass.
