FA20 Engine Swap

FA20 Engine Swap

Apr 29, '21

This blog post describes what we’ve learned so far (as of July 2020) about doing an FA20 swap into an older chassis like a GC or GD. While this swap is remarkable and unique, we do not currently recommend it. Keep reading to learn why. Our recommendation is based on the FA20 into a 99 Outback swap we helped with.

What is an FA20?

FA20 is the engine code for 2014+ Forester XT and 2015+ WRX motors. While these engines are flat four like most Subaru engines, they are direct-injected turbo motors, making them different from the EJ platform. Some other differences between the FA and the EJ are that the FA has a turbo in the front, fueling is a bit different since it’s return-less, has a high-pressure fuel pump on the engine, and the ECU is located in the engine bay.

Why is the FA20 a good engine?
The FA platform will be the future of Subaru, but from a swap standpoint, we aren't there yet. This engine has some great new features like direct injection, and chain drive, which means less maintenance, and it will have plenty of aftermarket parts. It looks to be a better platform and likely will build more power out of a stock power train as development continues.
Why is the FA20 so difficult to swap into older style chassis?

Wiring Perspective
The short answer is CANbus 2.0. CANbus is the electronic communication system in newer style Subaru models. V1.0 has been around since 2005 with the Legacy models and doesn't have much information passing through it. Since 2014 Subaru has added every input needed for the ECU to run correctly on the CAN line. This makes it difficult to swap into other cars (CANbus or not) because the ECU is looking for many inputs to work correctly. For example, the vehicle will not start if the ECU doesn’t get the information from the immobilizer system on the CAN line (key, cluster, and immobilizer box).

In addition, we can't use an older non-CANbus ECU to run this engine as we do with the EJ platform due to the direct injection system. It takes high amperage drivers in the ECU to control that that the EJ ECUs don't come equipped with. At this time, the only aftermarket ECU that works with the direct injection system of this car is the Motec standalone.

Another issue is the problem with flashing and tuning the FA20 ECU. After a swap, a tune is recommended to get any engine working correctly in the new chassis. Although it's possible to reflash, we had to band-aid the process for this, making live tuning impossible, thus making the prospect of tuning a daunting one.

Finally, a significant issue with the FA20 swap is the difference between how the ECU interfaces with the rest of the car. The way the ECU receives inputs and sends outputs to the other parts of the vehicle to run systems like cruise and AC work differently. Although there should be ways around them, it's just more hurdles that need to be addressed.

Mechanical Perspective

Many mechanical pieces will fit together with slight modification, like the exhaust, but many things don't.

Mounting the engine – intermediate difficulty. The outback sport cross member will bolt on, but the oil pan is a bit farther back on the FA, so you have to notch the cross member to make it fit.

Steering – One of the most challenging parts was that the FA has an electronic power steering column, compared to the EJs with a hydraulic power steering setup. This needs to be addressed one way or another. In this case, the owner chose to add a power steering hydraulic pump which took the place of the AC on the engine.

Fitment challenges – the axles were tricky because of the swapped FA transmission. This could be solved using an EJ transmission instead of the FA transmission.

Radiator fans – difficult to make work. The FA engine is longer than the EJ engines from front to back so the radiator fan had to be pushed forward and pusher fans placed on the front of the radiator instead of behind it in the engine bay.

Fuel – The FA20 has a return-less fuel system, so a Radium multi-pump fuel pressure regulator needs to be run to dial in the fuel pressure.
Low Mount Turbo – The low mount turbo in the front is very low, so a strong skid plate should be added to protect it.

What is the iWire Recommendation on FA20 Swaps?

It’s a very cool and unique swap, but we don’t recommend doing it yet. We suggest waiting a few years before attempting this swap so there are more parts and aftermarket accessories for the FA20 swap. A lot of the larger pieces did fit, but there was still a lot of custom work. For the wiring aspects there are still a lot of kinks to be worked out to have a reliable car with basic creature comforts. Also the cost is a bit high for this swap even though the engines sometimes can be found cheap. It’s most likely double the cost to do an FA20 swap as it would be to do a similar year EJ STi swap.

If you’re looking for an engine to tinker with for many years, you could do this swap but with the wiring and mechanical changes plus the time and money that will go into the car, we think there are better engine choices to swap into your Subaru. Our biggest tip if you decide to move forward with an FA20 swap is to purchase a full FA parts car. You’ll need pieces that are married together like the immobilizer system with ECU, key, body module, and cluster in the car to make the FA swap run properly.

If you want to check out the FA20 swap project car we’ve been helping with check out the YouTube links below. Please note that we’ve been working on this car for over three years and it is still not running and driving reliably, but that also might be due to the owner constantly tinkering with it too. ;)

Tags: Subaru Swap