A cat-back system will do nothing for you other than change the exhaust note. Go with an x or h pipe with cats. From what I've heard, the best mod is the gear change, 3.73 for 5 spd and 4.10 for autos.
------------------
************************
1999 GT - Laser Red
K&N, Steeda pulleys, & Steeda strut tower brace
(Upcoming mods: subframes (bought), Bassani X, & FMS 3.73s
|