I have heard the race magnum bullets on a 5.0 with 2 1/2" h-pipe and it is loud, a little louder than my 1 chamber flowmasters that I just had replaced with 3 chamber flows.
They are cool at first buy they get old real quick and after a while it wont seem quite as streetable as it did with your old mufflers.
If you want loud then get your self 3" exhaust because mine got a lot louder with the 3" and it sounds better.
Good luck with what ever you go with and keep us posted.
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James Cox
nochevy@hotmail.com
1991 Mustang LX
12.565 @109.38mph 1.764 60ft