My C-172L Skyhawk has been converted to the Power Flow Systems tuned exhaust. The old muffler(with attached carb heat box) is in perfectly good condition.
The system is sitting in my hangar at Wiscasset, ME. For more information, contact me. I have photos which can be e-mailed.
EDIT: Prior to the PFS installation the 'Hawk had been through a successful annual and its then-standard exhaust system met all specs.