I have a pair of dynomax muffs on my car and they give it a nice tone at idle and full throttle but quiet in side the cabin. Have never ran flowmasters but have some buddys that do and they sound good. I did start my car up when I 1st put it together and ran it around the block with open headers, it sounded like john force took a ride around the block. It rattled my neighbors windows and people I did not know came out of their houses to take a look. The dynomax units took care of that and never seemed to hurt the performance. I bought mine thru TTI.