Subaru Impreza GC8 & RS Forum & Community banner

Running a GD (WRX/STi) Cat-Back Exhaust on a GC8 (93-01)

100K views 146 replies 90 participants last post by  BuntaGC8 
#1 · (Edited by Moderator)
So I see all the time people wanting to run GD turbo exhausts and such on our GC/GM/RS's. Everyone tells them "yes, they will fit, however you will need to extend the midpipe and rotate a flange for it to fit." Everytime I read this, I think "why? then you can't re-sell it later?"

That brings me to this post, I'm sure a lot of you have figured this out and done it, but I would just like to put it out there for EVERYONE. Have an adapter made that will bolt up to your stock cat section AND the GD exhaust. That way down the road when you get tired of the catback or decide to go turbo, you don't wont have a problem selling or reusing your existing catback.

What are your guys' thoughts on this? Has anyone else done this besides me? Am I just over-thinking this a bit?

To illustrate this, my exhaust set up *my adapter is twice as long as yours should be! use this as an illustration ONLY please.*:
adapter

unchanged catback


measurements:
cat-adapter flange: 2.5"
piping: 2.5" stainless steel with taper to 3"
adapter-catback flange: 3"
I don't know too much about the flanges except that they are 2 bolt flanges (obviously). Next time I remove my exhaust, I can take actual measurements of the bolt holes if needed.
Ill also see if I can't measure how long the actual adapter is as well tomorrow.


*reason why MY adapter is twice as long as any of yours should be, is the catback I am running is a 3 piece design which has the taper its own separate piece. I just removed this taper section, and extended my adapter.*

Mods can feel free to move/edit this post if needed.
 
See less See more
2
#5 ·
I just had a custom midpipe made, my axle back didn't come with a midpipe or I would have gone your route.

If anyone does do this, you might want to think about using flex pipe instead of a solid pipe, so that the exhaust can move like its supposed to.
 
#12 ·
I'd take one. Only thing is that I'd need the correct size flanges on each side as I'm going to be running a Cobb EL header along with the WRX midpipe (I believe the flange on the high flow cat that came with the midpipe is larger than the cat flange, but I'm not 100% sure).
 
#16 ·
I was reading on the honda forums and the H22 guys have dyno proven charts that there 2.2 motors found gains in a 3inch exhaust over the 2.25 and 2.5.

the B series 1.6 and 1.8 motors were to small and 3inches is to big for that small of a motor. with that said.

I bet the 2.5 could see some nice gains with a 3inch exhaust
 
#20 ·
OH I MADE A STICKY! :banana:

haha glad to see everyone liked me idea, and to see some have already thought about this! I can take it off and get specs for anyone who needs it, since I am selling my Espelir anyway.

I think if any vendors do decide to make a run of these that would be awesome!
 
#24 ·
is there a difference between the older midpipes and the one on the 01 rs?

I had a 03 wrx exhaust and all it needed to bolt up was a different rotated flange. Same deal with the sti exhaust that i just installed. Neither needed an extended midpipe....
 
#34 ·
sorry i haven't kept this up to date, Ive been neglecting working on my exhaust lol

Sorry I do not have the angle of rotation or any other measurements available at this time.

I may be able to have a few of these made for those interested. Of course, I would likely need a vendor account, so I would like to see how many, if at all, would be interested to see if its worth it or not.
 
#41 ·
Well the N/A UEL header is completely different design than the turbo header. So you will need to replace the header regardless. Just run your OEM cat section with an Ebay replica Borla header for now to save cost.

a bit late to the party, but...
:lol: Why yes, I am.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top