Try making your own mousse can muffler. do a search on here for them, or listed as Mousse Can Pipe, or MCP. They are cheap, easy to make, quieter than a mac's pipe, and give a bit more boost. They are also tunable for your specific engine requirements. Also, mac's black pipes tend to be peaky at high rpms, so unless youre flying something at the top 1/3 of throttle, youre not going to be fully on the pipe. They will also be louder than a stock pipe, much louder to some peoples ears LOLOL.

Good Luck,
Steve