Or maybe the Muzzy exhaust effectively is an H-pipe type exhaust afterall, except that it is a single exhaust, so it does not have the other leg of the H that a dual exhaust would have. I don't know, I'm just the guy pushing the throttle lever. I have had a number of vehicles modded with headers and dual exhaust (V-10 Dodge, V-8 Jeep, etc.), and our local hot rod shop says that H-pipes don't do a thing, and they say they get their information directly from Doug Thorley himself. I would think that Doug Thorley would know how to build an exhaust. But then again, there are just as many other exhaust builders (Flowmaster for example) that say an H-pipe does help, mainly by improving low end response.