This guy solved his Subaru head gasket problem with a twin-turbo V12 swap

This man did a V12 engine swap on his Subaru WRX and it's officially insane. Build photos included!

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What’s not to love about a screaming V12, a pair of turbos and a BMW M3 dual-clutch gearbox?

It isn’t uncommon for the Subaru boxer engine to succumb to the dreaded head gasket issues, so when John Proulx picked up a 2009 WRX STI with an already blown motor, rather than go down the path of wasting any more time with the standard EJ25, he initially shoehorned the legendary 3.0L VVTi 2JZ-GTE from a Toyota Aristo (also found in the late model MKIV Supra).

This engine combination is about as far away as you can get from something that might result in an unexplained head gasket failure, so the choice was a no brainer.

Amazingly enough though, John was able to still retain the AWD system with the 2JZ swap. An incredible feat in itself.

Fast foward a few years, and he was bored of the 2JZ and decided to go for something a little more exotic, something that has never been done before, and something that is clearly a lot more complicated. It’s no wonder this is the world’s first and only V12 swapped Subaru WRX.

And so the V12 Toyota engine enters the chat. The V12 in question is usually found in the Japanese luxury Toyota Century limousine. Displacing 4,996 (309cu), the standard V12 makes a modest 208kW (276 horsepower/354 pound-feet of torque).

John tells CarExpert:

“I decided i want another challenge and thats when the V12 came to mind. I wanted to do something thats never been done before, i started doing research on that Toyota V12 from a Toyota century in Japan and when looking to buy one a local import shop had 1 in stock so i decided to go take a look at it and came back home with it the same day.

When it came to transmission choices, John elaborates: “While I was on the way to collect the V12 with my buddy I asked him what tranny could be cool to use, and thats where he mentioned the BMW Dual Clutch Transmission (DCT) from a BMW 335i & M3. So I did some research on the way to get the engine and as it so happens, you can wire a clutch by wire and do clutch kicks and burnouts with it like a manual trans. So I was sold on the idea.”

I found a used transmission in the same city as the engine and went and pick it up at the same time as the engine. Now came the hard part. I had to see if I could even get the engine and transmission to fit in my STI.

“The engine wasn’t too expensive, $3,000 Canadian. It’s the rest of getting it to work that’s expensive,” Proulx continued.

“Twelve 1,000-cc injectors, twelve coil packs, two throttle bodies, two turbos, two custom manifolds, a standalone ECU that can control all that plus the DCT transmission, wiring, etc etc.”

John knew it was going to be a tight fit, but he was confident he could make it work. Initially there were no plans to force feed the 5.0L (309cu) Toyota V12, but you know how project cars go. “Wheels and coil-overs” turns into full blown projects.

I was gonna keep it N/A at first just to keep the small rods in the block. But one thing lead to another, and before I knew it, I went with twin G30-770 turbos to save the bother of fabricating two different sets of manifolds for N/A and forced induction.”

When it comes to engine control, John says “I needed an ECU that could control 12 injectors, 12 coil-packs, 2 drive-by-wire throttle bodies, 2 wide-band O2 sensors’s and the BMW DCT transmission. The Maxxecu PRO Premium checked all the boxes.

The transmission is controlled by a customised set of paddles that live behind the steering wheel. It’s always a good idea to keep both hands on the wheel when you’re propelling a Twin Turbo V12 along the city streets or open highway. Although the transmission came from a BMW 335i, it is the same basic box as found in the M3, so running a TCU tune from the M3, and he has snappy shifts as per the ///M series counterpart.

Being that the plan was now a forced induction project, John purchased a set of 12 forged rods to prevent kicking the proverbial leg out of bed, but as yet he has not had time to fit them. So until that is done, boost is set to waste-gate pressure at a mere 8psi.

At only 8psi, the turbos are not even coming anywhere near their efficiency, but dear lord do they sound good coming on song!

“I threw the car on the dyno last week and it made 413whp and 455wtq at 4psi ramping up to 8 psi at higher rpms on 91 octane.”

12 spark plugs are fired up by a set of 12x Audi R8 coilpacks, and there is a set of 12x 1,000cc injectors supplying plenty of go-juice when needed.

I can tell you one thing, it is going to be a glorious day when John can wind up the boost to 20+psi in the hunt for 1,000+whp once it has the forged rods and pistons installed to relieve the stress on the stock units.

Unfortunately the sheer size of the V12 swap has meant John has had to do away with the AWD setup, opting instead to go with a RWD configuration using a Ford 8.8in rear end.

The end goal is 1000whp for next year when i build the engine so it supports it. The car is a street car after-all, I’ll go to the track for sure but its mainly a street car to cruise with my wife and 4 y/o son.”

Before you all jump into the comments saying how bad the weight distribution is, it’s nowhere near as bad as one might think.

Here’s a comparison between a stock STI and the V12 monster WRX, around 130kg heavier:

And the raw weight of the iron block 2JZ vs the All-alloy 1GZ-FE V12, yes they weigh about the same!

Lastly, the front to rear weight bias.

Stock WRX STI: (59%F, 41%R)

V12TT: (58%F, 42%R)

Well done to John and all those involved in the project, it certainly is one of the more unique builds we have seen come to fruition, and not just used as a paperweight at a car show.

For more information about the build, you can find some more pics, info and videos on John’s Instagram here: https://www.instagram.com/1lowrx/.

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Mark Trueno

Mark Trueno is a CarExpert Contributor.

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