Currently I have bbk shorties, the stock h pipe with the 4 cats (for emissions) and Mac pro dumps (just got em from a fellow stangnet member)....and it has no loudness to it, I just had dumped flowmasters on last night and it was a bit louder with them, but I heard flows are louder than Mac's anyways? All my friends have Macs and sound awesome even on a stock mustang, but is that just because they dont have cats? and I do?....I expected to have some of the nice deep Mac sound even with the stock h-pipe? but I guess you need to have no cats to have it sound decent? whats everybody using with their Mac's? cats or no cats? (btw I have an o/r x pipe but its off since I still have to finish inspection)