About Subaru's FA & FB engines

We have already learned about the classic Subaru engines from the EJ series and we have understood the generallity of how are those engines labeled. But it is a fact that time passes and is important to keep updated with the new developments. In this case, as the Japanese brand introduced a new series of engines with the BRZ and the last generation of the Forester, it is important to start thinking on the possibility that they start replacing the classic EJ series during the following years.

On the other hand a new Impreza is around the corner, and keeping in mind that the current model of the WRX came with the same BRZ engine, it increases the probability that the use of this platform of engines becomes a thing for the next generations of Subaru’s four-cylinders. For this reason is important for us to focus our effort on the FA & FB series and understand which were the changes compared to the previous EJ series.

But let’s begin with the basics. Why Subaru decided to replace the classic, reliable, popular and mighty engine? Simple: new technologies must be developed and it is important to go forward. And as the trend now is to create engines which are ecological, they decided to put their efforts on the development of powerful engines that could run on less fuel than the previous engines.

And was with that purpose that Toyota and Subaru decided to work together to create a sports car that was efficient and fun to drive as well. As you might know, that sports car is known by the name of BRZ for Subaru, GT86 for Toyota and FR-S for the recently deceased Scion. And they decided to fit an FA20 engine in it.

Before going ahead, you have to know that there are different FA engines, just like the nomenclature we had before to be able to recognize each EJ engine. So in order to be specific, you must know that the BRZ was available with the FA20D which is a Naturally Aspirated that can reach 7000 RPM and 197 HP. Also it reaches 205 Nm of torque. This engine features the Toyota’s D-4S technology which, in simple words, works by using a direct injector and a port injector for each cylinder, and are used according to the speed that the engine moves. This system works perfect with the valve timing system: the D-AVCS. Both work together to have low fuel consumption at low revs, but high performance at the high ones.

However the FA20 is not only available for the cars listed above. There is also an FA20F that is available in the USDM WRX since 2015, the JDM Legacy 2.0 GT and Subaru Levorg that is only available in Japan.

This FA20F is the same block of the FA20D, but it only has direct injection, and also is turbocharged. This one has a lower compression ratio; While the FA20D can reach a ratio of 12.5:1 the FA20F can reach 10.6:1 because of the material that are used. While the first one uses aluminium, the second one has aluminium for some parts and heavier cast iron for others like the cylinder liners. Also the shape of the piston rods are different compared to the older EJ series as these new engines feature diagonally splitted rods.

There’s also available an FA20E that is used in the Subaru Forester XT which doesn’t have the sport camshaft, the CVT and the ECU are programmed with different purposes. Also the turbo of the FA20F is tuned for a different range of RPM’s.

The thing now is that FA engines were not released alone. FB engines came by the same time that these were created.and the range here is wider. We can find an FB16 which is a 1.6 liter engine that is installed on the base model of the Impreza XV. Produces 116 Hp and 150 Nm.

Also FB engines are available in 2.0 liter engines, but these engines are specifically created to get lower fuel consumption. All these engines are naturally aspirated for the same purpose.
And compared with the EJ series engines FB look almost the same from outside. However the camshafts and the valves are placed in a narrower angle between them, and the rods and the crankshaft are different; Compared to the older engine, the FB has achieved a 22% of fuel saving with these slight changes.

The FB20 can be found in the Subaru XV, the Impreza and the JDM Forester and the as the FB20B which has 148 Hp and 196 Nm. On the other hand the FB20X is used in the Impreza XV Hybrid which produces 160 Hp and 221 Nm which works beside of an electric engine that produces 13 Hp. Are those numbers small for you? Don’t worry. It seems that Subaru made an STI concept of the XV hybrid. It hasn’t reached the production line yet, but let’s cross fingers and hope that it becomes real with interesting features.

There is also an FB25B which is available in some USDM Subaru Forester and Legacy. Is a 2.5 Liter engine and produces 170 Hp but its compression ratio is lower than the one of the FB20’s

This content was originally posted by a Car Throttle user on our Community platform and was not commissioned or created by the CT editorial team.