A while back I installed a set of Classic Chambered Exhaust Cobra mufflers on a 427W. Made a huge improvement in sound quality. The FFR mufflers were harsh and "blatty". And very loud. The new mufflers had a much smoother sound, more mellow, like an old 60's muscle car. Huge improvement.
They looked a lot better, too.
Not sure if it made more power though, as I made other changes at the same time.
