Originally Posted by themilman
your cat isn't that restrictive to start with, putting a hi-flow cat is going to make about 2hp difference from what I've read. For $600 you can get Crower Cams and springs and retainers, instant 10-20hp depending on your setup. Passing Smog is a problem with 403's and 404's.
Since this thread is 2 years old, I'm sure he's already done something with that $600.