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Old 08-07-2012, 05:14 PM   #1
Uruchima
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Have a Nice Day? 2009 2.5i Impreza Catalytic Converter

Hey Folks,

I'm trying to look for a High-Flow Cat for my Subaru 2.5i Impreza (hatchback) and I've looked at a fiche blueprint of the exhaust system--I was trying to find the size of the pipping--and I noticed the cat is attached to a pipe which then connects to the exhaust manifold (if I'm not mistaken)

here is the fiche for the exhaust:



I have a OBX WRX Catback Exhaust installed and I'm looking to get a high-flow cat but after looking at this fiche I don't know if I need a custom high-Flow cat or get something off a WRX or a Legacy Aftermarket.... any suggestions/ideas/help?

If it's just a high flow cat that I need, what is the length and in/out width of pipping?

Goal: High Flow Cat
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Old 08-08-2012, 10:54 PM   #2
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The cat is built into the header. Honestly, I'm pretty sure a HFC will do nearly nothing for you. If you'd want, you could either get some custom headers built (cough Rallisport Racing UEL headers), or you could chop up your stock header (which I definitely wouldn't want to be doing.
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Old 08-09-2012, 01:04 AM   #3
bugeyetex
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Change your goal to a high flowing exhaust system. Replace the whole thing, not just the cats if you want to do anything besides taking the sugar pill... Its not turbocharged, so you wont see any real gains unless you do the whole system.
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Old 08-09-2012, 02:11 AM   #4
alt14
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Wait for Rallisport performance headers and a high flow second cat.. or gut it, I won't suggest going bigger than 2.5 inch pipping though
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Old 08-10-2012, 11:10 AM   #5
Uruchima
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The obx wrx exhaust I have is 2.5in and also has a nice back pressure for exhaust velocity. Let's see when rallisport gets their headers. I will ask you this question, I'm getting ready to do a stage 1 tune...

Should I go to colder spark plugs like from a wrx, since I have to change them this weekend anyways?

I have a Cosmo racing CAI and the obx exhaust, stage 1 tune will be open source...
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Old 08-10-2012, 11:50 AM   #6
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Instant high flow cat system on the cheap....remove the 2nd cat completely. Technically you only need one but since the car has 2 cylinder bangs the EPA (or california) requires 1 cat for each bank.
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Old 08-10-2012, 11:58 AM   #7
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Quote:
Originally Posted by treksofar
Instant high flow cat system on the cheap....remove the 2nd cat completely. Technically you only need one but since the car has 2 cylinder bangs the EPA (or california) requires 1 cat for each bank.
Good thing I'm not in California... should I test pipe it? Or gut the cat?
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Old 08-10-2012, 12:04 PM   #8
treksofar
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test pipe. hell while ur at it just take the entire cat and midpipe/resonator section out and replace with a piece of 2.5" exhaust tubing.
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Old 08-10-2012, 12:06 PM   #9
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a good exhaust shop should be able to set u up for around $200 or less.
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Old 08-10-2012, 12:32 PM   #10
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Quote:
Originally Posted by treksofar
test pipe. hell while ur at it just take the entire cat and midpipe/resonator section out and replace with a piece of 2.5" exhaust tubing.
I have a obx cat back already, so straight pipe from the heads to the exhaust should be all I need...
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Old 08-10-2012, 12:34 PM   #11
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Any response about the spark plugs? I'm getting a stage 1 tune, should I upgrade them to wrx plugs?
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Old 08-10-2012, 03:17 PM   #12
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Quote:
Originally Posted by Uruchima View Post
Any response about the spark plugs? I'm getting a stage 1 tune, should I upgrade them to wrx plugs?
You're really not going to see chamber pressure/temperature in your engine that will warrent the need for cold plugs. Just use the NGK irriduim plugs spec'ed for your car and you'll be fine.
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Old 08-10-2012, 04:35 PM   #13
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Ngks like he said are all you really need
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Old 08-11-2012, 02:13 AM   #14
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Ive been looking at removing the second cat on my '10 impreza have not done it yet but alot of post Ive read suggest putting a resonator in place of the cat to keep it from getting to raspy.
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Old 08-11-2012, 02:49 PM   #15
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Got the ngks, oil change too, I'm racing next weekend, what I saw when I looked under the car that the cat has its own pipe detachable from the headers. I might see if can change that pipe out and see what happens. It'll definitely help my stage 1 tune.
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Old 08-13-2012, 01:07 AM   #16
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Quote:
Originally Posted by Uruchima
The obx wrx exhaust I have is 2.5in and also has a nice back pressure for exhaust velocity.
[annoyed]Backpressure does not induce exhaust velocity. Backpressure is bad, period.[/annoyed]
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Old 08-13-2012, 01:51 AM   #17
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Quote:
Originally Posted by Uruchima View Post
what I saw when I looked under the car that the cat has its own pipe detachable from the headers. I might see if can change that pipe out and see what happens.
There are two cats, one in the header and then the one your refering to. The second one is the one to remove / change and it is not monitored.
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Old 11-01-2012, 01:14 PM   #18
09subi2.5i
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Quote:
Originally Posted by Bababou View Post
There are two cats, one in the header and then the one your refering to. The second one is the one to remove / change and it is not monitored.
The second one is the one to remove for what reason? i have a stock exhaust on my 2.5i and i really am not looking to necessarily increase the sound as much as i just want to be able to employ that boxer rumble. i also would not like to void my warranty. what are my best options? i was thinking of a test pipe but after reading this i guess should i just do headers?
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Old 11-01-2012, 01:25 PM   #19
NH8991
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If you don't want to take the chance of having your warranty voided a claim denied then leave the car stock, period. (Very few people get their warranty voided, more often it's when you make a claim and Subaru won't entertain it on the grounds that your (insert modification here) caused/contributed to the failure.)

Yep, if you want the boxer rumble then you need UEL headers.
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