Hello. I have a 05 sti. Stock exhaust. My question is. Wats our stock pipe.2.5 or 3 inch. ..reason I'm going order a greddy ti c. Fatback. They said it will fit. But its a 80mm pipe. Can it fit directly bolt on is y i want some answer.i check alot of catback. It said 75 to 76 mm. Let me know if 80mm fits thank.