X-pipes produce a higher pitched noise than a H-pipe. They supposedly produce more power, but the gains are minimal. If you have flows, I would suggest the H-pipe, as the X and 40 series flows produce an ugly sound around 2300 up to 2800 that sounds just like an import. I have gotten used to it by not driving in that rpm range, but besides that 500rpms, it sounds so much better. I wish you could hear mine around 6700rpms.