If your going to get the off road y pipe, wich most do, You will also have to get the rear o2 sensors deleted '' for off road only of course. '' In the nelson tune so you dont get a SES light or Service engine light. I would go ahead and get the y pipe and just run 3'' all the way back to a muffler, then either dump it or run it out the side with some nice tips. Cheaper and I really think that it would flow better than a true cat back.