Uhm...w/out going headers, you could gut the precats. Some people say it has helped, other say it only helps if they are clogged (high mileage car) But if you've seen the pics I have of the stuff that in em...ew. Also, y-pipe mod is probably the best bang for the buck thing you can do...from free to like $40 tops if you bring it to a shop. I don't know too much about modding the main cat so I'll let someone else talk about that.
