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FA20 Engine Swap

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 cool and unique, as of now we do not recommend it. Keep reading to learn why. Our recommendation is based on the FA20 into a 99 Outback swap that we helped with.


What is a FA20?

FA20 is the engine code for 2014+ Forester XT and 2015+ WRX motors. While these engines are flat 4 like most Subaru engines, but they are direct injected turbo motors which makes them different than 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, as well as 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 just aren't there yet. This engine has some great new features like direct injection, chain drive which means less maintenance, and it will have plenty of aftermarket parts. All in all 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 it doesn't have a lot of information passing through it. Since 2014 Subaru has added basically every input needed for the ECU to run properly on the CAN line. This makes it difficult to swap into other cars (CANbus or not) because the ECU is looking for so many inputs to work correctly. For example, if the ECU doesn’t get the needed inputs from the immobilizer system on the CAN line (key, cluster, and immobilizer box) the car will not start.


In addition we can't use an older non CANbus ECU to run this engine like 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.


Another issue is the problem with flashing and tuning the FA20 ECU. In order to get any engine working properly in the new chassis after a swap, a tune is recommended. Although it's possible to reflash, we had to band aid the process for this which makes live tuning not possible thus the prospect of tuning a daunting one.


Finally a large 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 car 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

A lot of the mechanical pieces will fit together with some slight modification, like the exhaust but there are many things that don't.


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


Steering – One of the most difficult parts was that the FA has an electronic power steering column vs the EJs have 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 FA transmission being swapped in. This could be solved by 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 to 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 just 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 do decide to move forward with a FA20 swap - 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 in a reliable way, but that also might be due to the owner constantly tinkering with it too. ;)



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