[Mike Taylor 3601]

Not sure what kind of dyno you have,but Superflow has good sound proof info don't remember part# but donaldson muffler is basically 5'' big truck muffler about 4' long mounted outside,having as quiet in cell as you can get the better,want clean air not filled with exhaust.
The noise complaint we always have had is the buzzing sound from the exhaust fan,
Superflow has some info of more soundproofing things you can do out side to help,we just never did them.
The mufflers superflow reccomended did not hurt power at all.
Mike Taylor 3601