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Old 02-26-2011, 07:40 PM   #1
evoXtonic
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Default STi Catback Exhaust on my 07 2.5i

Hey guys,

I've looked and looked and can't find a definite answer for this so I'll deal with the flaming to ask it here.

I bought a used catback exhaust that someone had on a 07 STi and I was wondering if I'll have any problems putting it on my 07 2.5i. I have a mechanic friend that I asked before I bought it and he assured me it would be fine, but as I've been reading I'm getting doubts.

Anyone out there nice enough to help me out here?
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Old 02-26-2011, 10:07 PM   #2
awdorgtfo
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No. It won't fit. WRX and STI catbacks will need to be lengthened about 3 inches. The axle backs will bolt right up though.
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Old 02-27-2011, 02:50 AM   #3
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you can either cut where the resonator is and extend it or by the flange. I cut itby the flange for my sti cat back. this is how i did it. 2 1/2in ID.

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Old 02-27-2011, 05:58 AM   #4
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Got it. So I'm no good with welding and don't know anyone that is. Would it be better to have a shop do it for me?
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Old 02-27-2011, 04:48 PM   #5
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bmobs06, do you have a video of it installed?
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Old 03-03-2011, 08:53 PM   #6
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Yeah, I'm sorry I just need a little bit more info on this. So I have to cut the exhaust and weld it back together? I'm sorry I'm just new to all of this...
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Old 03-04-2011, 01:11 AM   #7
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I recently had an 04 WRX STI axel back installed on my 2.5i Impreza and it bolted right up with out any mods, but I wanted the something more, so I ordered a cat back system form Top Speed Racing. The only mod that you would need to do is cut the original flange on the cat and weld on a stainless steel flange the rest bolts on. I will post some pics up later and give you an Idea of how I did mine.
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Old 03-04-2011, 10:35 AM   #8
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Quote:
Originally Posted by DaWhiteScoob View Post
bmobs06, do you have a video of it installed?
no, sorry. i did do a diy. i'll try to find it.


Quote:
Originally Posted by evoXtonic View Post
Yeah, I'm sorry I just need a little bit more info on this. So I have to cut the exhaust and weld it back together? I'm sorry I'm just new to all of this...
yes, you have to cut it and weld it. you could just cut out the resonator and extend it from there but extending where i cut requires less pipe.
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Old 03-04-2011, 12:14 PM   #9
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Quote:
Originally Posted by evoXtonic View Post
Yeah, I'm sorry I just need a little bit more info on this. So I have to cut the exhaust and weld it back together? I'm sorry I'm just new to all of this...
My local shop extended my sti axleback for about $35. It took them all of 15 minutes. If you go this route, just make sure they DEBUR the cuts they make in both the centerpipe and small extra piece they weld in. it's really not a big deal but why not have it done right if someone else is gonna do it.
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Old 03-04-2011, 12:58 PM   #10
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stock na next to sti





i just took zaa zaa and cut it a few inches away from the flange.



go to autozone or something and get a 2 1/2in I.D. pipe and slip it right over, should be almost a perfect fit, then get it welded.





dont dick around with getting adapters; i did that and wasted a lot of time.
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Old 03-04-2011, 01:16 PM   #11
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This explains it all SO much better. Thank you guys.

I won't even go into details about how complicated I thought it was before reading these posts. This is much easier than I thought.
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Old 03-06-2011, 05:58 PM   #12
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Okay, I had an exhaust shop extend the midpipe for me - 30 bucks later I an ready to roll!

I'll post a video of it when I'm done putting it on.
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Old 03-08-2011, 03:09 PM   #13
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I'm looking to do this to my 06 2.5i but I'm only looking for the axle back... If I'm right it should just bolt right up, right? also does anyone know if this works for all years? Looks good, BTW
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Old 03-08-2011, 04:00 PM   #14
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^^ Axleback will bolt right up no problem, just use a new gasket!!

You will have no issues!
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Old 03-08-2011, 04:02 PM   #15
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I believe MY02 to MY07 have interchangeable axle backs. I have a 2006 WRX on my 07 2.5i. No modifications.
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Old 03-08-2011, 04:50 PM   #16
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Thanks guys... I had a friend who was going to sell me his but then I found out it was from a 2011 even it that would fit I dont wont quad tips lol... noobish question but you think an exhaust shop can order stock axle backs for me?
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Old 03-08-2011, 05:00 PM   #17
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Just search the classifieds. Best way to do it. I picked mine up for less than $25 and it looked brand new. With all the turboed guys, they upgrade fast and rarely keep their OEM. Gasket's a couple bucks. Swap takes 15 minutes. Then you're set.
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Old 03-09-2011, 12:33 AM   #18
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This is the stock when I finally got it off, after breaking a bolt and possibly my shoulder!




And this is the new midpipe with the extension:



And a close up of the extension:



And then a few pics of how it looks on my car:





Wasn't too hard after it was all said and done. Thank you all for the advice! Next step... sway bars!

Also, is that piece that's in the stock midpipe a cat? or just a resonator? Do you think I'll have to change it out in order to pass emissions?
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Old 03-09-2011, 01:51 PM   #19
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is there any benefit to using the STI axleback over the WRX? someone's offered me one for a WRX and I think I read that the STI is the way to go but cant' remember
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Old 03-09-2011, 07:00 PM   #20
DaWhiteScoob
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I think the 2.5i and WRX has the same pipe diameter, so it would do nothing. The STi exhaust pipe diameter is larger. 2inch vs 2.5inch?
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Old 03-09-2011, 07:22 PM   #21
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Believe it or not, I think possibly the baffles in the muffler section are slightly different between the wrx and STI axlebacks. I remember seeing a post on here or on a different board where a guy cut one of each open and the STI axleback flowed slightly better due to less baffles. I wish I kept the link, ugh.

And YES, the dia on the STI piping is only slightly larger, nothing that's gonna make a huge difference.
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Old 03-09-2011, 09:51 PM   #22
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ok.. I think I knew the diameter was bigger but was also pretty sure that there was more resistance in the WRX muffler. Guess I'll just wait for someone who has one for an STI. Not looking for a tremendous difference, I've seen them on youtube and it's cheap and sounds better than stock lol
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Old 03-09-2011, 11:28 PM   #23
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^^ Don't wait, the differences are so small, you'd never know in an NA either way.

wrx/sti axlebacks def look better, not really sound better but have a TINY more depth.

I'm uel and catless so on my car, big difference than if you're OEM header and catpipe, etc.

a wrx or sti axleback mated to UEL's and trackpipe or catpipe, can sound sexy but low key, maybe a tad to lowkey for most but I learned after many setups and I mean many, lowkey is far better than loud and obnoxious.
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Old 03-11-2011, 12:34 AM   #24
Nick88
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I would like better sound for sure but don't the 2.5i's lose power with the UEL headers?
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Old 03-11-2011, 02:54 AM   #25
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You have to have power to lose it...
I heard it's not substantially, if at all, noticeable.
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