With the caps in, the car was really quiet.Without the caps, they would probably sound the same. Seeing as it is a straight shot from the inlet to the new opening since the normal inlet and opening are offset.Essentially creates straight pipes.I don't think that the type of muffler will matter much since it is'nt going through the baffles.The warlocks have a piece with a gasket and three wingnuts that makes taking the plugs out quick and easy, but if you are wanting to make the effort to do the work on your current mufflers, I'd say go for it.