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Flowmaster 40 vs flowmaster american thunder


Well-Known Member
Anyone know the difference between these 2 in sound? One louder than the other..any input would be appreciated

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Resident Bracket Racer
I have 40s in the beast. I'm not sure of the difference but the 40s sound great! There's not much inside of them so they open up and have quite a rumble. I like them because the idle volume isn't excessive like in an SLP loudmouth. My .02