A while ago I took it upon myself to swap in a Phase II Version II 4eat from a 2003 WRX, mainly because I was tired of blowing through the poor selection of used version 1 4eat transmissions I could get my hands on around here, and it seemed like fun.
It doesn't seem like a ton of people (or maybe anyone?) has done a phase 2 swap, but luckily people have swapped the SVX engine into cars with the phase 2, which meant some info was already out there, and I knew it was at least possible.
I am just going to kind of post information as I get the chance and hopefully walk you guys through everything from transmission / tcu selection, wiring, and whatever else.
First I am going to start with a brief overview of the differences between phases and versions of the 4eat transmission, along with VTD and MPT center diffs, torque converters, and flex plates. There is a ton of wrong information out there on this stuff but this is what I have verified from personal experience, along with trial and error.
First off we have VTD and MPT center diffs. The center diff controls how much power goes to the front wheels versus the rear wheels, and Subaru has three main types they use. The first is a "classic" differential that looks like the one in the rear end of any old car. This is only really used in the manual transmission so I won't talk about it further on here. The MPT center diff is the most common and it is a so called multi plate clutch setup. It provides a power split of 90% to the front and 10% to the rear under normal conditions, and the tcu can control it to allow up to 50% of the power to go to the rear if it needs to. This came in all USDM SVX cars, along with pretty much any non turbo Subaru automatic aside from the VDC edition Outback.
Here is a picture of an MPT Diff
The VTD or variable torque distribution center diff works completely differently. It has a strange looking planetary center diff that allows a power split of 45% to the front and 55% to the rear under "normal" conditions. The computer can lock up a clutch pack in it and force a 4WD locked mode if it desires it. It is easy to tell the difference between a VTD and MPT transmission based on how the center diff housing looks at the back of the trans. The transmission computers are different between a VTD car and an MPT are different as well, although mainly in terms of programming I think.
A picture of a VTD center diff. (not my pic, I forgot to take one of mine)
Now for the transmissions themselves.
We have the classic 4eat Phase 1 transmission. This came in all of the SVX cars, along with any automatic 4 speed Subaru before the year 1998. It is a partially electronic shifted transmission that uses a dropping resistor for line pressure control and features a brake band for the 2-3 shift. There were several changes to the casting of the valve body and some other details like the number of clutch plates and types of seals used inside based on both the year, and the car it went into. These only came with an MPT center diff, with the exception of the JDM SVX Alcyone which had some sort of unique VTD setup. I have not been able to get my hands on one of those sadly. The Phase 1 tailshaft / center diff housing / center diff is unique to the Phase 1 and none of those parts from a Phase 2 will work, in fact none of them are even close to working. I learned this one the hard way. The torque converter on a phase 1 is also unique and you can't swap them between phase 1 and 2. Same goes for the oil pump extension on the end of the torque converter.
Next we have the Phase 2 Version 1 4eat. It came out in 1998 and was used in all of the automatic Subaru's until it was slowly phased out in favor of the Version 2 around 2002-2004, although it highly depends on model and its important to check if you are unsure about yours. It, like the Phase 1, is a partially electronically shifted transmission. It still uses dropping resistors for the line pressure like the Phase 1, but it uses two instead of one. It uses a completely different valve body than the Phase 1 and no parts can transfer over. It also obviously is controlled differently, and the TCU from a Phase 1 will not operate a Phase 2, and the other way around. It ditches the brake band and only uses clutch packs, which in my opinion is a way better design. They also are generally a ton more reliable and can tolerate a lot more power without any issues. The Phase 2 Version 1 mainly came with an MPT center diff. A Phase 2 Version 2 rear diff housing / tail shaft assembly / rear diff will swap onto a Phase 1 Version 1 without issue, and the other way around is true as well. These are visually easy to tell apart from the Phase 1 because they have a spin on filter on the drivers side of the trans (aside from the H6 cars which had a cap instead of a filter in its spot)
Finally we have the Phase 2 Version 2. It started being used from 2002-2004 depending on the model / package. These are what subaru calls "direct drive" transmission which means the shifts are fully computer controlled. There are no dropping resistors or anything like that on these. The computer is in direct control of all shift points along with line pressure at all times. This can have some major benefits as you may imagine. The valve body from a Phase 2 Version 2 is different from a Version 1 and they will not swap over. The internals are mostly the same, and as I said before the tail shaft / center diff will transfer over from Version 1/2 just fine. They still have the spin on filter on the side. The VDC Outback along with the turbo Impreza/WRX got a VTD center diff, while all of the more basic sorts of cars got the typical MPT setup. The computers for the Version 1 and 2 transmissions are very different and absolutely will not work from one to the other. They are pretty hard to tell apart from the Phase 2 Version 1 transmission on the outside so it's super important to just look up the model number on the trans case, or the car it came from.
Here we have a picture of a Phase 1 from a 97 outback (bottom) and a Phase 2 Version 2 from a 2003 WRX (top).
Finally we have torque converter and flex plates. Like I said before, it's important to know that the torque converter from a Phase 1 will not work with a Phase 2, and same thing for the oil pump extension shaft. The converter and shaft are the same from a Phase 2 Version 1 to Version 2 though. There is a difference between the converter on a 2.0 and 2.5/3.0 car however. The converter for a 2.0 is a bit smaller than the 2.5/3.0 one and requires a slightly smaller flex plate to match it or else it won't bolt up. Make sure yours matches up before you put the trans and engine in the car or you will be sad because it won't bolt together! Luckily you can use either a 2.0 or 2.5/3.0 converter with a 4eat Phase 2 regardless of what engine its donor car had. In the same way, you can also use either a 2.0 or 2.5/3.0 flex plate on an engine regardless of what size it is. That being said, probably try and use a 2.5/3.0 torque converter on the SVX because it makes a lot of torque compared to a 2.0
It is also worth noting that every 4eat I have run across has had the same total length, meaning that no driveshaft change or mounting point change is needed.
Next post we will get into the actual swap itself, starting with selection of the transmission and TCU.