Quote Originally Posted by JJ91284 View Post
A good running gtp can and will run a 3.5 pulley fine with no KR or very little. Now if your cat's plugged, then you could run into problems.
I have to disagree with that. Lot's of people have 3.5" pulley setups that should in theory be able to run a 3.4" pulley no problem, but yet a lot of them still have KR problems. Hell I still have quite a bit of KR even with my setup, but that may have to do with it being winter and everything. Yes people used to be able to run 3.5" pulleys on near stock cars with little to no KR, but nowadays that is extremely uncommon.

So my point is if your car isn't a factory freak, then select pulley sizes conservatively.