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Old 06-22-2010, 01:00 PM   #1
sittinsideways
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Default stromung cat

i have borla headers and an 05 cat with 2.25 piping back. im considering the stromung cat cause of the "up to 9%" gain in fuel economy. im doing a considerable amount of driving a day now since school started. does any one have this setup and have they noticed a fuel gain?

thanks
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Old 06-22-2010, 01:38 PM   #2
EdHilario
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Won't make a difference.
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Old 06-22-2010, 02:50 PM   #3
Audi20Tdriver
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What type of exhaust do you have? I have never heard someone want to add a high flow cat primarily for MPG gains . I wouldn't do it personally if it is a daily driver, unless you are looking to squeeze out the max power gains possible for the N/A. Depending upon your exhaust setup it can make it much louder and much raspier sounding.
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Old 06-22-2010, 02:54 PM   #4
ruckus racing
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stromung cat, or cat-back?
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Old 06-22-2010, 03:23 PM   #5
kero
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I will tell you this, I have UEL's with a trackpipe (no cats a all) on my setup, and I did see a gain in gas mileage and a gain in power with both turbo xs and current 07 wrx axleback.

I am warning you though, if you have an aftermarket catback or axleback of any kind, you're gonna be quiet loud if you go the trackpipe option. With the UEL's, trackpipe, resonated centerpipe and turbo xs axleback, I was noticeably louder than many of the modded wrx's/STI's on my local club. Merging on the highway or getting up to speed was unbearable due to the crazy loud burble I had. It wasn't raspy as the double res's took car of that, but LOUD.

I had to sell my turbo xs and put back on a 07 wrx axleback to quiet my car down, and add to that a double resonated STI centerpipe to boot. Now my car is quiet enough to drive daily without getting a headache or agitated.

The stromung HFC is really designed for 06/07 NA's going to the UEL setup since out stock catpipe didn't work with the setup. 05 and early ppl still use them but I can't tell you it's the norm as the 05 and earlier OEM catpipes fit perfectly with the UEL setup.

Oh one last thing, should you consider a trackpipe (I doubt you will though), you will have to deal with the dreaded P0420 cat deficiency CEL, which I had a local tuner remove permanently from the ECU map.

Last edited by kero; 06-22-2010 at 03:29 PM.
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Old 06-22-2010, 04:48 PM   #6
o'doyle
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I have an 04 2.5ts with borla UELs and the stromung hfc. Works great, slightly raspy--and I'm saving up for the stromung axleback at the moment. Haven't noticed huge anything gains at the moment, since the front half of my exhaust is flowing WAY better than the back half. Once the muffler swap is done, I'll reset the ECU and probably see some gains finally.

Sadly, my "upgrade" was just a clogged OE cat and blown out exh. manifold gaskets that happened to be cheaper to replace with performance parts than OE parts

Muffler once I get hired somewhere full-time. Ohphleaseohpleaseohplease...

If you go with the Stromung HFC, you'll have to do something about the longitudinal drive shaft's heat shielding bolt that sits RIGHT on top of the HFC's cat section. Either remove the bolt & find some 14gau. baling wire to hold it up (invites buzzing issues, IMHO), or do what I did and just take the damned heat shield off. It's shielding your longitudinal drive shaft from your exhaust heat. Your longitudinal drive shaft is a big, freaking solid steel bar. Pretty sure it doesn't need a gay little aluminum wafer to protect it from your big, bad exhaust temps. Subaru thinks your drive shaft is like:

Oh, and find out where your rear o2 sensor is. If it's 3" from the front one in the first cat like mine was, you'll need an o2 sensor extension harness. Caspers electronics FTW, but *send them pics of your stock connectors!* I didn't remember to do this, and they overnighted me one with WAY wrong ends. Fail. Probably my fault for assuming "subaru o2 extension harness" was going to be universal. Whoops.

If you choose to splice it yourself, please do a better job than the mechanic that did mine did the first time. He screwed something up and the rear sensor threw p0137 AND p0138 at the same time, which makes no sense if you know what those mean. I got him to re-wire his splice, and it works fine now.

The p0420 can be defeated by the Rallitek mechanical fix, too. Got one on my car, it's not coding at all now.

Good luck & have fun
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Old 06-22-2010, 07:32 PM   #7
scoobysnacks420
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^^ How do you reset the ecu? I just put a catback on my 08 n/a and its really quiet, I was thinking about buying a HFC to make it louder plus the supposed gains in performance, my headers are stock equal length so do you think it will be loud or raspy? anyone know? sorry to throw thread off course I just had a similar question
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Old 06-22-2010, 07:41 PM   #8
kero
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For the OP, mechanical fixes do not work on 06/07 NA's, such as 02 spacers, etc etc.

Our ECU's are different than 05 and earlier.

The top has been covered and is this section.

That is why I had a local tuner edit the stock ecu map.
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Old 06-23-2010, 12:23 PM   #9
PA-Outback2000
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i have the random tech dual cat. i did notice gains in mpg. i have an intake header, cat, and catback. i get about 30mpg on the highway. i managed to get 32mpg on the way to long island last summer. it won't bolt right into +05 cars without getting the borla/knockoff header. u can make it fit, but u need to modify the piping slightly. there r o2 sensor fixes if u have to meet emissions where u r.
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Old 08-15-2010, 08:43 PM   #10
Ryan2442
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Question Stromung Exhaust

I was wondering if any of you guys could help me out since we're talking about stromung exhausts. I have an 07 2.5i and was looking into the stromung exhaust at Boxer4Racing.com, but it doesn't have the full cat-back system, just the axle-back portion. What would I need to make it a cat back if I bought the axle back? Any brands and part names would be appreciated. Thanks in advance
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Old 08-16-2010, 06:47 PM   #11
RaceFaceXC
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Quote:
Originally Posted by Ryan2442 View Post
I was wondering if any of you guys could help me out since we're talking about stromung exhausts. I have an 07 2.5i and was looking into the stromung exhaust at Boxer4Racing.com, but it doesn't have the full cat-back system, just the axle-back portion. What would I need to make it a cat back if I bought the axle back? Any brands and part names would be appreciated. Thanks in advance
The Midpipe, a stromung one, which is literally right on the same page you saw the axelback on. And that 9% gain is with headers also. The headers are really the source of the MPG gains. And it's probably with a tune.
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