Hipo... I ran/run the spintechs with a dr gas x and thought they sounded pretty good.More of a high pitch/rpm sound..a tone change happens at about 3000 rpm for me...sounds like its turning more rpm then it is.This is the first x ive tried and changed to many other things to know if it helped or not.I just switched back to my old Flowmasters and an H pipe and want to test it out at the track....Im hearing lots of different responses of what people like.Flows are a much deeper tone for sure.