All different kinds of mufflers available.All of the glasspacks are basically the same.Back in the old days I preferred the Hollywood Belonds,and a lot of the guys swore by Smitties.Then there were the Cherry Bombs and probably about a dozen more brands on the market.And they all sounded mean.On my 55 I have headers and Flowmaster mufflers which give it a very deep throaty sound.On my 72 I have headers and Magnaflow mufflers,they sound much more like the glasspacks of yesteryear,they really beller when I step on it.Flowmaster and Magnaflow are expensive,compared to glasspacks.All ya gotta do is look thru any of the glasspacks and you can see they are all about the same,and they definitly get louder after being used for awhile,almost like straightpipes.