You most certainly could. With a WRX though, I would highly recommend you purchase a STi axelback to replace your stock. I have one for sale if you're interested :bigthumb:
Alex i didnt know you were selling the axel back..... i think i want it.... ill call you later today im going to be up that way....
I originally upgraded the down pipe on my wrx and kept the stock axel back. I really didn't like the setup; you could hear it being baffled where it transitions from 3" to 2-1/4". I was given and am currently running the sti catback with my 3" invidia downpipe and I'm very happy with the setup.