That's an extremely radical cam for a street engine. Other than installing a set of very quiet mufflers such as the ones used on mid-1970s Cadillacs, there's not going to be much you can do to quiet it down. There's just too much unburned fuel getting into the exhaust system and being burned there during coasting to do much other than install super-quiet mufflers to stop the noise. One muffler for a big Cadillac engine, a 472 or a 500 with 2 1/2 inch inlet and outlet nipples, will produce very little back pressure, and duals with the same muffler will be quiet, and VERY low restriction- - - -the only thing they won't do is make noise.
Jerry
