Yeah, go with 2 chamber (I think it's the 40 series muffler) Flowmasters. I don't know exactly what's in the American Thunder kit so I can't tell you bout that, but I can tell you that you will get the full effect (sound! and flow) of flowmasters with off road H-pipe. I LOVE mine.
“…because, no one’s really gonna be free until nerd persecution ends.” ---Revenge of the Nerds
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'79 Mustang Coup
4" Cowl
Weld wheels (15x6;15x8)
Stock 5.8L
C4 w/ shift kit
1.5" MAC full length headers
Holley 750 CFM
Edelbrock intake
2.5" Off road H-pipe
8.8" Rear end w/ 2.73:1 gears (sucks!) (awaiting installation of 3.55s)
Front: 225/60/15 Rear: 255/60/15 Eagle GT II
Sucky Purolator air filter that's choking my car.
