wrapped jdm r header and CarSound hi-flow cat vs the old setup The R header and 2.25" hi flow cat should be an improvement in performance (more flow) and sound (less) versus the stock GSR/straight pipe setup. A 2.5" cat is also a good alternative for more high rpm flow, at the expense of a louder system. Why am I so concerned with sound? Two reasons. One: I don't like getting exhaust fix-it tickets. Two: I don't like arriving at my destination with my hearing dulled from the constant droning on the freeway.