I had FlowMaster single, double, and triple chambers on a Mopar 360 V8 with Doug Thorley headers.

The single and double chambers were too loud for highway cruising at 75-80 MPH.

I'd listen to a Borla Stainless-steel set (www.borla.com).

:-) neil
1988 360TE AMG (Brabus muffler)
1993 500E (Remus muffler w/center resonator)