I have a magnaflow 2.25". Performance wise, for around town, it is better then my old 2.5" straight through system. This is on a VR6 mind you. But why? Because of SCIENCE (ie, volumetric efficiency as already mentioned). It had crap low end, and insane top end. But you cant pull 6k rpm in peak hour (...without being a tool). I cant imagine anything above 2" will do you much good on a 4cyl though.
Anyway, best of luck with your decision!
Anyway, best of luck with your decision!
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