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Old 11-18-2015, 02:51 AM   #1
Scooby Newbie
Member#: 432960
Join Date: Oct 2015
Default Ej257/ej253 build and swap. Opinions and advice wanted

Ok here goes, I have a 07 2.5i with rebuilt title so not worth the sell-buy a WRX thing.
I got the car for $3k, I also have other cars I can use for Daily.
So my plan. Please let me know what else I need/am forgetting
Use the ej257 shortblock I have and my ej253 heads with upgraded studs and gaskets.

Parts I have;

Ej257 I bought for $450 included engine wiring harness to bulk connection. Heads and cams, tgv's and other misc (not using) only using the shortblock.

WRX injectors $60


Sti struts with race comp springs $200

Whiteline racing 24mm sway bars w/bushings and end links $200

Catless bell mouth downpipe $20

WRX header and up pipe $100

Nameless strut tower bars $30

Fedanza LW flywheel (buying matching stage 2 clutch) and LW crank pulley.

Parts I'm buying in the next few weeks;

WRX turbo (any suggestions?)

Walbro 255

WRX fuel pump housing and lines.

Head gaskets and studs

WRX cat back exhaust.

Parts I'm reusing (if possible)

2.5i intake manifold (will gut tgv's and use for spacers if needed)

2.5i ej253 heads

2.5i ECU reflashed for WRX or open tuned

2.5i periferials I.E. A/C, alt, ps

2003 forester water pump with extra coolant passage for the turbo and oil cooler for turbo (modified hose routing) or is there an easier way to get oil and coolant to the turbo cuz I'd love to have the oil cooler functional as well 😉

That's all I can think of for now. Please chime in and let me know what else I need besides modding my crossmember (tons of fab exp.) easy for me.😁

Please hold your sell/buy a WRX comments to yourself. Doing this for personal satisfaction as well as other reasons other posters have mentioned.
Thankx in advance

And props to all my fellow swappers willing to put in hard work and defy what others shy away from.

Edit: also buying a good BOV and electronic boost controller.
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Old 12-28-2015, 04:40 PM   #2
Scooby Newbie
Member#: 432960
Join Date: Oct 2015

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Old 12-28-2015, 05:42 PM   #3
Scooby Specialist
Member#: 68647
Join Date: Aug 2004
Chapter/Region: MAIC
Location: Richmond, VA
07 STI 35R


What do you want out of the car? What kind of power goals do you have? What kind of fuel do you plan on burning? What kind of budget do you have to spend to get to said goal? Is your EJ257 just case halves that you plan on building up or keeping it stock? WRX injectors will not allow for much power, neither will a WRX intercooler. And when you say 2003 Forester water pump, is it new or actually a pump that's 13 years old?

My biggest piece of advice is decide on a goal before making any purchases.
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Old 12-29-2015, 05:09 PM   #4
Scooby Newbie
Member#: 432960
Join Date: Oct 2015

I would just like to get some good power out of the car as I lost a lot of low end torque with the current setup.

I plan on burning 91octane

The injectors I bought are sti injectors

I've decided to go with the Sti water pump and route the water for the turbo from elsewhere.

I also have bought a front mount intercooler for the sti

The block is stock and I'll run it that way.

I have already bought most of what I need other then fuel pump and ecu/and accosiated wiring.
My biggest hurdle now is deciding if I want to open source tune or not. I would prefer to swap in the wrx Ecu.
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Old 12-29-2015, 06:57 PM   #5
Scooby Newbie
Member#: 291441
Join Date: Aug 2011
Location: Houston
2004 WRX


Will an 07 wrx ecu plug into your existing wiring harness? The electronics side of this could be the hardest part.

I have an 04 wrx with a V7 sti drive train and ecu. Everything works and was "easy" because the ecu came from a car with the same harness. I don't know if your car has the same wiring harness as the 07 wrx does. That would be the first I would research because it will determine which ecu you can use which determines which intake manifold which could effect which heads you can use.
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Old 12-30-2015, 03:42 AM   #6
Scooby Newbie
Member#: 432960
Join Date: Oct 2015

That's what I've been trying to figure out. I am prepared to swap the harness if I absolutely have to. But the plugs and pin count look the same. So idk? I've posted another thread asking about it as well as searched endlessly for over a month on the net. But I still don't know. Didn't get any response on the thread either.
I have a set of ej257 heads and engine wiring harness just have to get a intake manifold. But I'd rather go with the sohc of possible. Emissions are no problem as I have property in a town that does not require emissions testing.
I also have a set of ej251 heads, but I don't know if they are even worth considering using.
If I use my ej253 heads and a wrx Ecu I will loose my avls anyway so maybe the 251's are worth using. Idk
Any suggestions on head choice?

Does anyone know if I can swap just the engine harness and plug in a wrx Ecu? And maybe add or turn off the immobilizer?
I can get an Ecu keys and immobilizer for a good deal. But finding a usable Ecu harness is proving difficult and id rather not Tare my dash out if possible.
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Old 01-09-2016, 12:36 AM   #7
Scooby Newbie
Member#: 432960
Join Date: Oct 2015
Default Ej257/ej253 build and swap. Opinions and advice wanted

Ok so I picked up an 07 wrx ecu. And it does plug in to my harness. So my question is now. Can I just change the engine harness and swap the engine?
Also how would I go about adding or bypassing an immobilizer? Since my car didn't come with one it won't crank with the new ecu. I tried
Also jumped the starter and its cutting something else IE: fuel/spark.
I'd like to get this figured out before I start my swap. So any help would be MUCH appreciated!
Feel free to PM me since I know we shouldn't be posting stuff that will help thief's steal our cars.
I can provide proof of ownership of my car if you need. (Picture of my registration and license)

Last edited by Subaru4you; 01-09-2016 at 05:42 AM.
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Old 05-01-2016, 08:39 PM   #8
Scooby Newbie
Member#: 380680
Join Date: Feb 2014
Location: washington
2006 Impreza 2.5i
navy blue


Figured anymore out?
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Old 05-10-2016, 04:28 AM   #9
Scooby Newbie
Member#: 391438
Join Date: May 2014
Chapter/Region: VIC
Location: Vancouver
1999 Forester SF6
Acadia green


understand that an ej257 is a dual over head came set up. the 253 is a single over head cam set up. the ecu works in tandem with which ever set of heads it was wired with.
i'm doing a similiar build, but sticking with sohc heads on a 257 block. your best off going the same route. problem is, you have to find someone who can reprogram an ecu for it to work.
you also forgot a turbo subframe and the accompanying headers
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