I never ran my car before my mods, so I don't know about the gains. As far sound, you'll get a deeper exhaust tone at idle and driving. 80 Bucks is a little steep, but not too bad. I got my cat, S pipe, 02 bung and I pipe all installed for 75 bucks. Try to find a cheaper mom and pop muffler shop. Screw midas, meineke, etc.
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2000 BLACK FIREBIRD 3.8 A4, (Stock 3.42 Gears, LSD, W68 Pkg), 160* Powerstat, Whisper CAI & Lid, K&N Filter,
3 Catco Highflow Cat,
3in. S Pipe, 2.75" Dynomax Catback, Sprint Springs, BMR STB, LCAs & Brackets, 18" Mondera Wheels
MOFBA/FASTLOUIS Member... 1/4 Time: 14.981 @ 89.66 MPH