Ive got a powerflow exhaust on my valver, its a cat-back system, and im very happy with it. I was a bit sceptical about getting one ( i mainly did because it was a 10min drive to powerflow, or 2hr to predator), but the workmanship is excellent, and the sound is also good (not too loud, but has presence). I have noticed no drop in power, and no noticeable improvements either. You can specify whatever you want to them and theyll do it. Also get a lifetime warranty. There have been a few dissapointing powerflow efforts that ive seen, but im happy with mine.....hope that helps a bit..