wouldnt that be illegal if some sort o authority finds out?
Was that a joke?
Hacking the stock mufflers is at least as old as the 60s, and probably twice that old. The method used is made harder now by the integral tips on the OEM Mustang mufflers. It was to have a skilled welder (any welder will be if you ask him) carefully snake in and cut a hole into the side of the tube that shows in the outlet end. The usual size quoted was "a quarter" as in 25 cents.
Now, even as well-worn a sicko as me has never actually seen this done. Anyone that has? Neat picture of the stock V6 muffler, NBK.