Dad and I put a cable operated muffler bypass on the then-single exhaust on my 65 Barracuda. Came from J.C. Whitney. It leaked pretty bad, so we removed the flapper and Dad cut an oil can or something and clamped it onto the bypass outlet. Well, it wasn't too long before the cap blew off. So I just left it off and drove it for a couple of years with an open bypass. Of course, a lot of the exhaust just went on to and through the muffler, but it was still pretty loud. I thought it sounded good, and I never got a ticket for the noisy exhaust (speeding yes, noisy muffler, no).
I did get a ticket for loud mufflers after I swapped in a 340 and ran dual exhaust with Thrush glass packs and no tailpipes. They were loud, too.
I like my cars a little quieter today. . . .