I ran a set of smitties on the flathead 6 with 2" duels, it was obnoxious, swapped out the mufflers for two borla XS turbos and was very nice, had nice mellow tone idling and driving and didnt get real obnoxious when wide open. I also have the same mufflers on my 67C10 but 3" on a 427 small block pushing 550hp and I can listen to the stereo while cruisinng 65-70mph, they will also let you know I am coming if I go wide open throttle. I am also running the same 3" on my 48 with an LS1 that I ended up putting an additional cheap set of turbo mufflers for resonators to help tone it down just a tad more (should have went with 2.5").
