I have Flowmaster 40's with H-pipe and they sound great... they did have to break in though... course when I first got them I went to a chop shop and the dumbass doing it put a 2 and 1/4 inch pipe on the driver side (our stangs have a 2 and 1/2 inch pipe) and he didn't connect them through and X or H pipe so they sounded ricey as hell at high RPM's then I went and got it fixed with an aftermarket '05 mustang pipe and a custom H pipe and now I love em! Can't wait to get headers