Borla R1 mufflers, is what my friend has on his GT and is sounds awesome.
www.borla.com should have more info if you want
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'97 GT, full lenght MAC headers, MAC Pro chamber h-pipe, Mac 2.5" Cat-back w/chrome tips, AODE 4W70R, K&N, Eibach springs and a 150 NOS wet shot system. Blue/Black/White interior, 1500 watts of music power. Coming very soon, shift kit, 4.10 gears, aftermarket trany pan, custom chip from SVC, Norman's lower conrol arms and subframes, and new pollygraphite bushings for the front suspension.