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Mach V customer Stephen came to us with a query: Did we think it was possible to swap the powertrain components of a late-model Subaru WRX into his 2020 Subaru Crosstrek? If so, would Mach V Motorsports be willing to take that project on?
Above, the Crosstrek as it sat before the project began.
We were a little reluctant to try to undertake this challenge. We have seen people take on projects like this and run out of resources -- time, storage space, and of course money -- and we have also seen projects run out of steam when the logistics and complexity just overwhelmed a person's capacity for managing or concentrating on all of it.
Also we worried that the amount of time involved would just make it infeasible -- we have experience stripping cars to resell the parts, and it is almost unbelievable how much time that can consume, between having to be careful not to break the parts as the car is disassembled, to the labor involved with labeling and organizing all the bits.
All that said, this SHOULD be -- in theory -- a pretty straightforward swap. Both the current WRX (chassis code VB) and the 2020 Crosstrek are based on the same architecture, known as Subaru Global Platform. The floor pan of the car is basically the same. (We confirmed this a little later on; see below.)
Still, at least at that point in time it had not been done, and any time you are on the cutting edge, it's going to take even more time than you think, and there are bound to be pitfalls and hurdles you can't anticipate.
Before we went any farther into the discussion, we decided to see for ourselves how similar the cars were underneath. We put Stephen's Crosstrek and our 2022 WRX up on two lifts in the shop, side by side, and got out the measuring tape.
We measured every important hard point we could think of -- front to rear and side to side distances between suspension and subframe pickup points, control arm dimensions, track widths. Every dimension we checked was a perfect match. We were confident the physical parts of the two cars could interchange.
Stephen offered to bear a good bit of the up-front labor by disassembling the cars at home, as far as he could without a chassis lift.
Mach V agreed that we would manage the heavy lifting of removing the powertrain from the Crosstrek, removing the powertrain from the WRX, and installing the WRX engine/transmission/front subframe into the Crosstrek chassis. We would also wire up the resulting hybrid.
At that point Stephen set about looking for a suitable donor WRX. He found one for sale at auction that had been damaged in the rear quarter panel, so all the mechanical parts were in good shape -- even the rear suspension on the crash side was unharmed. He purchased the salvage car and had it trucked to his home. The swap project had begun.
That's the crashed 2023 WRX donor car, above, as it arrived from the auction. Note blown side curtain airbags. Since the impact was up at the belt line of the car, the mechanical components were in good shape.
Stephen got quite a bit done at home, including completely gutting the interior of the both vehicles, swapping the rear subframes and suspensions of the cars, installing the WRX bulkhead wiring harness and body control module into the Crosstrek, and installing the WRX dash beam and other interior accessories into the Crosstrek. All this turned out to consume quite a bit of time (and garage floor space) on his part.
The photo above shows the WRX main wiring harness laid in to the Crosstrek shell.
Here's what the interior of a modern WRX looks like once you remove the seats, dash, center console, steering column, pedals, dash beam, door cards, and wiring.
(Just as an aside, there's a generous amount of insulation visible with the interior out of the car. That helps explain why the current WRX is so quiet inside compared to the older generation cars.)
Once the cars were to the point where they were ready for the drivetrains to come out, both vehicles were brought to our shop by flatbed.
We set about removing the engines/transmissions/front subframes from both cars.
Once the rear windows were operational, perhaps our most difficult task was to get the airbag system operational. There were several sub-challenges to this.
First, the donor car had been in a crash, so unsurprisingly, the airbag control module had fault codes showing "Rear passenger crash detected." We would have to diagnose and whatever was causing that fault state.
Secondly, just as with the windows, the rear seatbelts were different between Crosstrek and WRX. The 2020 Crosstrek had simple "dumb" seatbelts, with traditional inertial locks; the WRX, on the other hand, had pyrotechnic pretensioners -- effectively an explosive charge that would go off when an impact was detected to tighten up the belts in anticipation of a crash.
Since we were using the full WRX wiring harness, BCM, and airbag control unit, we needed WRX-style rear seatbelt modules to wire up and make the airbag module happy. Later model Crosstreks have the same type of active tensioners as the WRX, so Steven sourced some rear belt units from one of those cars. Further complicating things, the updated belt units don't mount to the car in the exactly the same way as the old ones, so the brackets had to be lightly customized to work.
Once we got all the proper parts on hand, we powered the system up, hoping that the un-crashed seatbelt units would solve the airbag control unit's fault state. Despite the new parts, the airbag module was still showing a fault, and we could not clear it with our shop computer scan tool. We suspected that the crash indicator was designed to be a non-clearable fault. (We admit we can understand the manufacturer's logic here.) Even Marc at the body shop was unable to cure the module's fault code with his most sophisticated aftermarket body module scan tools.
We eventually ended up removing the airbag module from the vehicle (which of course requires full disassembly of the dash) and mailing it away to a company that specializes in this kind of thing. They cleared the fault codes and mailed it back to us, and when we re-installed the module the airbox system started up happy and with no fault codes.
Finally we were ready to fire the car up. It started right up!
There is one detail that as of this writing is not complete, and that's the exhaust. What's on the car at this time is all stock WRX exhaust, including the Y-pipe at the back of the car, but not including the mufflers, because of course those are designed for a car with a trunk.
The custom cat-back exhaust that WAS on the car previously will not fit directly to the stock WRX J-pipe. So the plan is to have Stephen's favorite custom exhaust shop modify the front of that cat-back system to join to the WRX J-pipe section.
Here is the finished project:
One question that we get a lot, is why not modify the car? Why put it together using all stock parts? We know the FA24 turbo engine can make pretty good power with aftermarket modifications. The car is at this point almost completely put together using OEM hardware -- with the exception of the suspension, it's all original equipment Subaru parts, including the entire engine, the brakes, the wheels, and the exhaust system, or at least as much of the exhaust system that would fit on the car.
The short answer is budget, but there's a little more to it. Besides being expensive, this kind of project is VERY complex. We have basically built a car from the bare unibody up, and the level of detail and the quantity of parts to organize, store, and keep track of is very high. Adding the additional confusion and potential troubleshooting issues associated with putting aftermarket parts on at the same time seemed like inviting trouble, so we were pleased to limit the scope of the project to OEM parts, at least for the initial building of the car.
After Stephen's bank account recovers a bit from the project, and once he's been able to do some shakedown driving on the street and lived with the car for a bit, the plan is to get the car back in for some additional aftermarket performance parts.
Another common question is, could the average garage or home mechanic perform an equivalent swap? We would say that while it might be possible, it would be very difficult.
The biggest challenge is probably space and time for organization. The amount of parts that go into these cars is in the thousands. It took a HUGE amount of time to organize those parts, and they consumed a large amount of real estate in both the Mach V shop and in Stephen's home garage. You could probably bin up a lot of the parts, but then you would be trading more TIME (sorting, packing, unpacking) for less SPACE taken up.
This was one of the most logistically complex projects our shop has ever undertaken. We used various notes, spreadsheets, and checklists to keep track of all the details. See our whiteboard, above.
Difficulty number two is the fabrication skills required. Anyone who does the swap the way we did will need a high level of wiring skill, along with body fabrication capabilities and custom welding abilities for the exhaust system. We outsourced two out of three of those, but these days finding a body shop to do custom work like the fender merge is difficult, and quality custom exhaust work is similarly challenging to source.
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