Getting my factory pre-cats replaced tomorrow with some 45 degree straight 2 1/2" pipe. I still have my stock mains back to a flowmaster "Y" pipe" to single 2 1/2" straight pipe "turned down" before the axle with a 3 1/2" stainless tip. I'm hoping to get a deeper, louder exhaust note with improved performance and fuel mileage. I believe my pre-cats were damaged when I had a bad O2 sensor setup from the factory which had me driving extremely rich for over 4,000 mi. till they could get it fixed. Even with straight pipes my exhaust isn't that loud. My gas mileage also dropped to 14 MPG highway. I think the "Max Performance" tune is harder on the pre-cats as well with the hotter EGT's. I hope this helps while still keeping the air clean. I will post results. This is info I have been looking for, for a long time now and there isn't much on the boards that I found.

 

good luck with it Jackl. What shop did you get to do it for ya?

 

Dunno if I should share that here...you can PM me if you're interested.