2.5 inch DP, 3 inch cat - How?

[dashtz69]

I was looking at buying a 2.5 inch O2 eliminating downpipe from RNR to hopefully have no creep. Then I was going to have a custom made 3 inch cat-back done around here at a local exhaust place, but how would that work. I would like a high flow cat, but are there ones with 2.5 on one side and 3 on the other? Or even a straight pipe made like that? Thanks

 

[Mystic511]

If you're getting a downpipe from RNR making sure that it's not one that eliminates the cat. I'm pretty sure all their downpipes assume you're removing the cat all together. I called RNR when I ordered my exhaust and had a 2.5" testpipe made to go with my 2.5" downpipe. I figure i could replace that testpipe with a 2.5" high flow cat when i needed to.

I got RNR's turboback system, so I asked them to mate that to their 3" catback.

For you though, it depends on if you're going to run a 3" high flow cat or a 2.5" high flow cat. The 3" ones will be slip fit, so you'll probably have to cut off the flange on the downpipe and find a piece of exhaust pipe that goes from 2.5" to 3". Then on the catback side, you can just slip fit the cat on.

If you're gonna do a 2.5" cat, I'd just have a flange on the catback for 2.5" again using a piece of exhaust pipe that goes from 2.5" to 3" and weld a flange onto that and make the catback from there.

 

[boostedinaz]

I would just but there entire system for simplicity sake. Just get it in all 2.5 and I bet you will be very happy. Plus it will come all at once and you wont have to worry about the fitment issue.

Most 3 inch cat backs will have lenghtend holes in the flange as will the cat you are using so that they will bolt up. If you are taking it to an exhaust shop let them worry about it.

Michael

 

[theycallmebruce]

RRE makes a downpipe that has 2.5" from the o2 to the flex section, 3" flex, 3" after the flex.

 

[WhiteTsiAwd]

All you need to do is get a Reducer or in your case an Expander. However their still the same thing.

Im making my own exhaust to save some $$ and so i can have it made the way i want. Just get a 2.5"-3" expander or reducer and you are fine. Thats the easiest way to do it. I think their $12.89 from Summit Racing.