91 vert GT - no engine mods - 2 front factory cats ( rear cats removed ) x pipe , OEM headers , car has 2 regular type looking mufflers ( I cant see any brand markings ) car sounds good like it is , but I want a bit louder . I have used flows 40s decades ago and remember they sounded good with 4 OEM cats and the H pipe ( but they did seem to pop a lot down shifting ) . I heard some spins 9000 on long tubes no cats and they sounded good . Can I just change one muffler to a flow or spin without causing the heads to have a lopsided amount of exhaust flow? My thoughts would be the X part of system would balance the pressures -