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Old 05-06-2009, 09:45 PM   #1
blk6s
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Default 2.5i factory header cat delete

I made this last night, just for fun. I was running Borla headers and a RalliSport cat delete pipe for a few months, but the wife was getting a little tired of the rasp/resonance. It seems like everyone wants a direct replacement header for the 2.5i, but since the factory one is already EL, a aftermarket one would be basiclly the same as the factory one minus the cat. So for a little experiment I dragged the factory header out, cut off the cat, then fabbed up a 2.25" stainless pipe/flange/o2 bung. This bolts directly to the factory cat pipe (second cat). Oh, while making this, my vise broke, then I ran out of tri mix welding gas for my mig, which is why it looks a little crude.
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Old 05-06-2009, 10:20 PM   #2
2.5i
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Holy Crap dude, thats freaking killer how much time do you have invested into that? Maybe you should make another. Dide you notice a power gain?
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Old 05-06-2009, 10:36 PM   #3
blk6s
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Well, I started after my kids went to bed, and didn't finish until three in the morning. (lots of fun going to work on two and a half hours of sleep) I would make more of these, but am having a difficult time finding them. the butt dyno says that they feel about the same as the Borla/cat delete pipe combo, but with zero rasp/resonance
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Old 05-06-2009, 10:41 PM   #4
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doesnt throw any codes?
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Old 05-06-2009, 10:46 PM   #5
Jerry Xu
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Quote:
Originally Posted by blk6s View Post
Well, I started after my kids went to bed, and didn't finish until three in the morning. (lots of fun going to work on two and a half hours of sleep) I would make more of these, but am having a difficult time finding them. the butt dyno says that they feel about the same as the Borla/cat delete pipe combo, but with zero rasp/resonance
So are you saying there is felt improvement over the stock header before the gut?
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Old 05-06-2009, 10:54 PM   #6
blk6s
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Quote:
Originally Posted by scoob2.5i View Post
doesnt throw any codes?
I guarantee it will throw a code. It hasn’t been on the car for even a day, but the cel will eventually come. Right now I’m using the o2 sensor spacer I was using on my previous cat delete pipe. That allowed me to run anywhere from one to three weeks before getting a cel
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Old 05-06-2009, 10:58 PM   #7
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Quote:
Originally Posted by Jerry Xu View Post
So are you saying there is felt improvement over the stock header before the gut?
makes the car a lot happier after 4k
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Old 05-07-2009, 08:18 AM   #8
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NIce piece and wait the stocker isnt cast iron??????? Well Well Well how did you get the bend ? nice flange.
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Old 05-07-2009, 12:16 PM   #9
Jerry Xu
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is there room for a HFC in there instead of the pipe? This may help cel issue.

Last edited by Jerry Xu; 05-07-2009 at 01:47 PM.
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Old 05-07-2009, 01:43 PM   #10
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Stepping to an OBX/Ralltek/Cobb or TWE header will yield different results, mainly longer runners and probably a little more low/mid torque.

Raspiness can be fixed with the addition of a small glasspack in the midsection piping.
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Old 05-07-2009, 06:25 PM   #11
blk6s
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Quote:
Originally Posted by GEE-OTTO View Post
NIce piece and wait the stocker isnt cast iron??????? Well Well Well how did you get the bend ? nice flange.
I own RalliSportRacing.com so I had all the materials on hand
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Old 05-07-2009, 06:33 PM   #12
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Quote:
Originally Posted by Jerry Xu View Post
is there room for a HFC in there instead of the pipe? This may help cel issue.
With the high flow Magnaflow cats I have in stock, no (I tried). Mabey a smaller HFC such as a pre-cat might fit
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Old 05-07-2009, 06:40 PM   #13
Jerry Xu
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might need to use something like RR to disable the cel's as they show up.
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Old 05-07-2009, 06:46 PM   #14
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Quote:
Originally Posted by blk6s View Post
I own RalliSportRacing.com so I had all the materials on hand

Really Wow dude where have you been ive been looking for a guy to make my stocker (2008 legacy manifold) to a UEL once I got under my car and realized that it isnt cast iron ive had the fever but no equip All i want to do is make that bend straight and chop out some length on the passenger side collectors to make it UEL is that what you plan to do ?
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Old 05-07-2009, 09:49 PM   #15
blk6s
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Quote:
Originally Posted by GEE-OTTO View Post
Really Wow dude where have you been ive been looking for a guy to make my stocker (2008 legacy manifold) to a UEL once I got under my car and realized that it isnt cast iron ive had the fever but no equip All i want to do is make that bend straight and chop out some length on the passenger side collectors to make it UEL is that what you plan to do ?
I don't plan on altering these headers any further, sounds like your interested in a design similar to the Agency headers for the wrx?
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Old 05-08-2009, 09:27 AM   #16
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Quote:
Originally Posted by blk6s View Post
I don't plan on altering these headers any further, sounds like your interested in a design similar to the Agency headers for the wrx?

Nah I just want a N/A header that will bolt up to our stock exhaust like you have made but UEL for the rumble instead of a RS type header that does not. . One day someone will make them for 06+ N/A Impreza/LEgacy
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Old 05-09-2009, 01:41 AM   #17
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Cant wait to get my Mid-pipe and finally get them on! once that card works
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Old 05-09-2009, 12:20 PM   #18
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Default Gc8

Would something like this fit on a GC8 or would the water pump outlet get in the way?

I like the idea, seems better then the borla/obx/ect. route when it comes to long term strength.
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Old 05-09-2009, 12:44 PM   #19
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why not just leave the first cat since it has the o2 sensors and remove the cat in the cat pipe since its unmonitored?
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Old 05-09-2009, 03:49 PM   #20
blk6s
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Quote:
Originally Posted by jordan s View Post
why not just leave the first cat since it has the o2 sensors and remove the cat in the cat pipe since its unmonitored?
Excellent point. In my case, I'm going to replace the second cat with a resonator. Here's a pic of the factory cat I removed. Notice the flow coming out of the cat practically slams into a wall.
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