Will changing out just the mufflers (not the exhaust piping) still be legal to be in stock class autocross or will that put me into a different catagory? I'd look it up but I can't find my book.

 

I'm pretty sure you can do anything with the exhaust past the cat. Some national level drivers have dryer venting as their "exhaust" in stock class cars.

 

No problem, everything after the CAT can be replaced. The exhaust has to exit the vehicle to the rear, so even a straight pipe would be OK if the noise isn't too loud (and it probably would be).

 

CoralDoc is right. You can do a number of cheap things though. Try cutting a stock system off after the resonator and then just run pipe back to the RH exit. That at least gives you a resonator to quiet it down. You can also put a downward turn at the end of the pipe to send the exhaust noise straight down. If you can find a cheap, used exhaust someone is getting rid of you can keep your stock system intact in the garage or basement and cut up the other one.