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Discussion Starter · #1 ·
Hey all!
I have a 2001 Subaru outback; 4 cylinder 2.5 liter automatic. I'm currently slowly but surely in the process of swapping an automatic 2004 2.0 wrx motor into it.
I just can't seem to figure out if I should be using the transmission from the wrx or if I can safely use mine (are the internals/ ratios the same in both transmissions)?
Also will I need the rear differential from the wrx?
Trying to gather the information I need as my fiance and I are rebuilding the wrx motor.
Thanks!
 

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2005 OBXT Limited, VF37, STI intake, 5MT
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For ease of "plug and play" compatibility, you will want to stay with the original drivetrain (trans, diff, electronics). The 4EAT from the WRX is wired differently enough that a large harness merge/piggyback is required to interface with the original electronics. Plus, the VTD center diff requires its matching TCU to operate properly.

However, I am curious as to how you're going to do the engine management for the EJ205. If you're going to just use the whole harness from the WRX, then I'd use the matching trans, diff, and TCU. The 4EAT in the WRX is more heavy-duty than the 2.5L 4EAT.

If swapping to the WRX trans, you will need to swap the rear diff. IIRC, 04 WRX 4EAT is 4.111 and the 01 2.5L OBW 4EAT is 4.444.
 

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2002 3.0 VDC Wag + 2018 2.5 Leg Ltd
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seems like your fiance wants to go blind on wiring diagrams, ...and maybe done around November.


whats wrong with your 2001 now?
2001 Subaru Outback options, prices, all currrent and older Subarus Outbacks Foresters Imprezas Bajas

a whole lot easier to sell everything you got now and buy a 2001-2004 H6 powered car listed as needing head gaskets,
and drop a $600 JDM H6 (212hp/210torque) engine into it.

as that little 2.0 turbo has to work really hard to shove around a 3500 lb car. vs. the 3100lb car it was made for.
(227hp, 217torque ...when wrung all the way up)
2004 Subaru Impreza WRX and STi spec page

and typically to do this kind of swap you need a whole wrecked donor,...(and any wrecked WRX, or WRX parts typically goes for higher money then other subaru things). ...little things like a impreza WRX gauge cluster custom stuck into the legacy dash add up.
 

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2008 Outback wagon, 2.5i Touring
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I just hope for you that don't have the newer version of the 4EAT like I tried to swap 2 years ago
the car never ran except in third gear safe mode or reverse
 

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Discussion Starter · #5 ·
Rough diamond,
Thanks for the input. That actually helped out a lot.
My transmission came in all versions of Subarus from 1995 to 2007, and at that it definitely looks like it will hook up properly. With them being the same transmission, the only thing I can imagine being different is the gearing ratio, nothing on the bands or clutches; correct?
I'm just hoping it doesn't go into safe mode as it did with the 3rd guy down, but we have the ECU and the entire wiring harness for the WRX and as long as everything is wired correctly I can't imagine that being an issue.
 

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Discussion Starter · #6 ·
Alain B, I'm just hoping because the transmission is native it doesn't go into safe mode. Did you ever end up resolving your issue? We do have the ECU and the entire wiring harness for the WRX so was just wondering if you had those at the time.
 

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My transmission came in all versions of Subarus from 1995 to 2007, and at that it definitely looks like it will hook up properly.
Looking similar is about the only thing the 4EATs share in common with each other from 1995-2007. Subaru actually did about 6 different major versions in that time frame.

The WRX has a Phase 2, Sport Shift transmission. The closest compatible are from the Forester XT and Baja Turbo. However, those also have different final drive ratios. The trans will physically bolt up with the transmission crossmember, axles, and driveshaft, but that's about it. Electrically, it is quite different from your OB transmission.

With them being the same transmission, the only thing I can imagine being different is the gearing ratio, nothing on the bands or clutches; correct?
The Sport Shift (and Phase 2 turbo trans) have different valve bodies, transfer clutch systems, shifter, and torque converters. The turbo trans also have an extra forward drum friction that the "pedestrian" 4EATs don't have.

I'm just hoping it doesn't go into safe mode as it did with the 3rd guy down, but we have the ECU and the entire wiring harness for the WRX and as long as everything is wired correctly I can't imagine that being an issue.
Without the WRX's TCU, wiring, and shifter, you will be stuck in limp mode (3rd gear).

I think more reading/research is in your future. Your biggest hurdle is having a rock-solid plan-of-attack when it comes to integrating the wiring and engine management. You will need the WRX's ECU and TCU for the engine and transmission to work correctly as they also work together, electrically. You won't have to worry about an immobolizer, but that's about the only "gimmie" Subaru is going to give you with respect to this swap.
 

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Discussion Starter · #8 ·
Hey rough diamond,
Thanks again for all the info. It looks like we will be using that transmission then because it seems to make the most sense. We do have the wiring harness, ECU and the TCU. We pretty much got everything we would need out of a donor car that was being scrapped after it was stripped out. The only thing that we didn't get out of the donor car was the rear differential and CV shafts. Other than that though we pretty much got most of the drivetrain.
We've been doing quite a lot of looking around and research although sometimes it's simply helps to ask those who have more knowledge on the matter like yourself. We have a friend who is very good with wiring, my fiance rebuilt his very own motor in his Subaru, it's just trying to piece together what we need to make this function in a car that this motor isn't native to entirely.
 

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Discussion Starter · #9 ·
Rough diamond:
Hwlp me try to understand what you're saying here. Are you saying that I should probably just use the transmission from my WRX? Or are you saying I'll be able to use my stock transmission in my current outbaxk as long as I have the TCU from the WRX transmission? That would mean I also have the torque converter because I possess the transmission from the WRX.
 

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Rough diamond:
Hwlp me try to understand what you're saying here. Are you saying that I should probably just use the transmission from my WRX? Or are you saying I'll be able to use my stock transmission in my current outbaxk as long as I have the TCU from the WRX transmission? That would mean I also have the torque converter because I possess the transmission from the WRX.
The easiest way to put it is like this:

If you're going to use the OB transmission, use the OB trans, OB diff, OB TCU, and OB wiring. You will need to do more custom integrating with the WRX ECU, which may not pan-out.

If you're going to use the WRX transmission, use the WRX transmission, WRX diff, WRX TCU, WRX shifter, and WRX wiring. This will requires less ECU/TCU integration (as it's already done), but you will now need to source a Sport Shift shifter (an H6 Outback MAY work/have one) and a WRX diff.

Hopefully, the harness wasn't cut anywhere near the dash, firewall, or shifter from the donor car. The WRX's OBD2 network requires the carefully calibrated wires to be intact, otherwise you will get error codes and/or things won't work correctly.
 

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but you will now need to source a Sport Shift shifter (an H6 Outback MAY work/have one) and a WRX diff.

Hopefully, the harness wasn't cut anywhere near the dash, firewall, or shifter from the donor car. The WRX's OBD2 network requires the carefully calibrated wires to be intact, otherwise you will get error codes and/or things won't work correctly.
H6 outbacks only had 4 speeds on the regular gated shifter from 2001-2004, no sport shifter on the 4EAT.
(H6 5EAT had it, in the 2005-2014. but that is a 5EAT).

I think the a 4 speed sport shift was only in baja sport and baja turbo, maybe a early forester XT. and the early WRX.
 
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Alain B, I'm just hoping because the transmission is native it doesn't go into safe mode. Did you ever end up resolving your issue? We do have the ECU and the entire wiring harness for the WRX so was just wondering if you had those at the time.
I solved the issue by trashing the whole WRX sport shift transmission and putting a JDM VDC transmission

good thing the seller ,who shipped me the wrong transmission, did me a full refund

search for my swap threads they are still on the forum, 2 of them
 
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