I had just no res for a while, not a huge difference. Now I have no res and no muffler and can't wait to get bigger pipe and a dynomax muffler. I say save your money until you get a good exhaust system. At least a svt exhaust or 2.25" single exhaust with a high flow muffler. At most, header, no cat/hi-flow cat, and 2.5" pipe with hi flow muffler.
