[Labmember0003]

Now its time for getting into the swap.

I will say right now the hardest part of the swap by far was the electrical side of it and so most of the time here will be spent explaining that, so that hopefully anyone else who wants to do this doesn't have to spend a week of evenings reading through decades old forum posts and trying things until they work.


First though I will start with the process of actually selecting your transmission. Although they can be a lot harder to find, I highly advise trying to find a Phase 2 Version 2 with the VTD center diff. The Version 2 gives you a much better control system and the difference in shift feel between a Phase 2 Version 1 and Version 2 is very real.

For my swap I got one from a 2003 WRX that had low miles that had met an unfortunate fate.

Other things you will need to make this happen is the TCU from either the car the trans came out of, or one with the same phase, version, and center diff. It is also important to know if it came from a 4 or 6 cylinder car. Either one will work but it does matter for later on. You will also need to get a flex plate to match the torque converter size your new transmission has. These can be found for cheap on Ebay but make sure it is from a car with the right engine size cause the listings lie and say they are all the same. You should try and get the transmission harness from the donor car. This also differs between both phase and version, and a Phase 2 Version 2 harness can be really tough to find as I found out. I ended up getting only the transmission and TCU pigtails and had to wire in the middle part from scratch (something which you kind of have to do anyways to an extent, but more on that later). You also need a bit of extra trans cooler hose to make it reach to your cars trans cooler, and you should replace the spin on fluid filter while you have easy access.


As far as the physical instillation of the transmission goes, it is really just the exact same as installing the stock SVX transmission. I won't go too in depth into it because there are plenty of threads covering transmission removal and instillation on the SVX (I wonder why...). Only thing I will mention is I just want to say one more time to make absolutely sure your flex plate and torque converter match up before you put the transmission in. You don't want to find out the hard way that the bolt pattern is a tiny bit different after the transmission is all mounted in place.


The electrical side of things gets more interesting, and is where the majority of this projects complexity lies. Pretty much you need to take the TCU from your donor car (in my case a 2003 Subaru WRX) and match it up to both the transmission and the SVX ECU. I actually took apart my SVX TCU, desoldered the three connectors from it, and used it to make an adapter so I wouldn't have to hack up the wiring harness in my SVX.

The first part is actually super easy. Both the original SVX transmission along with the WRX Transmission have two connectors on them. One feeds into the valve body / speed sensors, and one goes to the range switch. The one for the range switch is the exact same between both transmission so you can just plug it in and have that part out of the way. The one for the valve body is a totally different connector, and in fact the WRX transmission that I am using has 4 extra wires / pins than the SVX has. Originally I planned on running 4 new wires through the firewall and using the existing wires.

In the end I chose to run a bundle of 17 new wires through the firewall to go to each of the 17 pins on the valve body / speed sensor connector.


For getting the WRX TCU wired up, you obviously need to run its 17 wires down to the transmission like I said before. That is just a simple matter of looking at the WRX wiring diagram (I will attach at the end) and wiring it up to the transmission like it would have been from the factory in the WRX. Getting it wired up to the SVX power / grounds / ECU inputs and outputs is a bit more complicated and you will need to essentially compare the wiring diagrams from either car and use the i/o chart to get everything matched up. (I will include those for the WRX and SVX as well). If you use a Phase 2 Version 1 transmission from an Outback or something, you will need to do a lot of this part on your own since it won't match up exactly to mine.

Pretty much the transmission, just like in the old days, relies on two inputs for most of its decision making. Engine speed and throttle position. It gets the throttle position from the throttle position sensor. This is literally just a raw sensor input and so the new TCU can understand it just fine. The engine speed is a pretty simple signal as well. It is just one wire and the ECU sends a pulse every time one of the coil packs fires, and the TCU gets the signal and it does some math. It can figure that since its a 4 cylinder engine there are 2 pulses per engine rotation and it turns that into engine RPM. The issue is however that unlike the WRX, the SVX uses a 6 cylinder and so there are actually 3 pulses per rotation. This means that the TCU's calculated engine RPM will be 33% too high. This will make it shift at the wrong points which wouldn't be ideal. Luckily this is a pretty common issue for transmission / engine swaps and so you can get a generic rpm corrector board and dial it in for the right amount to fix the issue. This also lets you do another fun trick. You can get a second rpm corrector board, set it to skew the signal past where it should be and trick the TCU into thinking the engine is revving slower than it actually is. You can connect up a relay or a logic board to swap between corrector boards at the press of a button, and suddenly you have yourself a working power mode button which essentially tricks the TCU into shifting at a higher RPM when activated.


You also obviously need to hook up the cruise wire to the cruise wire and the ABS wire to the ABS wire, but thats pretty obvious from looking at the wiring diagrams. Power and grounds are pretty easy to figure out and there are plenty enough fuses in the SVX to make it all work nicely. In the VTD setup the FWD fuse doesn't get used because there is no way to force FWD. It is AWD all of the time. There are also obviously 7 wires that lead into the TCU from the combo meter / range switch to let know what gear you have selected. These also wire up in a pretty self explanatory way based on the wiring diagrams. Same for the ATF temp warning output from the TCU to the combo meter, the brake pedal switch, and probably a few other ones that I have forgotten at this point that just match right up.

The Speedo signal from the TCU to the Combo meter is just one wire, and it matches right up, but if you simply connect it and forget about it then you will find it doesn't work quite right. The speed signal is the same format but it is way too high from the new TCU and so the speedo will read way higher than what you are actually doing. This can be fixed by getting a speedo corrector board and wiring it between the TCU and the Combo meter, then dialing it in with a gps speedo app on your phone while you are driving.

Finally there is the dreaded torque control. The TL;DR of torque control is that shifting while the engine is making lots of power can blow your transmission up so right before it changes the gears the TCU is like "hey ECU quit making so much power for a quick second" and the ECU cuts back the engine power while the shift happens and it makes your transmission last longer. The SVX setup has one torque control wire, but the WRX setup has 3 torque control wires named Torque Control 1, Torque Control 2, and Torque Control 3. I simply hooked up Torque Control 1 on the WRX TCU to the single Torque Control wire on the SVX ECU and although it set a code, it works just fine and the shifts are not too hard by any means. If anything they are a ton smoother and more controlled than the stock Phase 1 transmission.

I am sure there is something for the wiring that I am missing here because it was really a huge ordeal. If you want to try this project yourself and need help with wiring just let me know and I can probably find you the diagrams you need and help you match stuff up.