How to understand the nomenclature for Subaru EJ series engines

As some might know Subaru stands out for their boxer engines that are installed in their flagship vehicles; The Impreza, the Legacy, the Outback, the Forester, the Tribeca, and their most recent creation the BRZ have one of those.

However not every Subaru is the same. Each of the models mentioned above has different engines and depends on its version that the engine is designed for different purposes. They do not only change on the number of the cylinders as some have four cylinders and others have six.

Today we will focus on Subaru’s most famous engine series and we will try to understand the difference between each engine.

Let’s begin with the basics: Subaru have produced many four cylinder engines…

… And not only horizontally opposed pistons engines, but during earlier years of the brand they had the EN series which was released in 1988 and was used basically for kei cars.
This one came as a replacement for the EA engines that were built from 1969 to 1994, which were already boxer engines.
We have also the newer engines: The FB engines which were recently released for Subaru XV, Forester, some Legacy models and FA for BRZ, Levorg and some Legacy models as well.
There are also the EE series that are 2.0 L diesel engines with 147 Hp and 258 lb ft.

However this is not yet what really concerns us. We are here to understand the EJ series which has been used in most of the Subaru rally cars until now.

The EJXX series are known for their reliability and for their longevity. But notie something in the previous sentence: I wrote ”XX” to point that there can be written two numbers, that represent the displacement. For example It is common to hear that the WRX STI has a EJ25 engine. This means that it has a EJ series engine with 2.500 cc displacement

But this is not always precise. Even if it works for EJ15, EJ16, EJ18, EJ20 and EJ25 (EJ30 was also a thing but did not reach the production), there are other engine codes that tell about the number of valves, if it is an SOHC or DOHC, or even if it is turbocharged.

Here is where codes become a bit complicated because Subaru decided to develop EJ engines in two phases. Phase I EJ engines are those engines from 1989 to 1998 and are known because the nomenclature has a letter at the end.

For example: EJ20G which was a turbo engine used in the Legacy GT, RS models (Until 1993), some WRX STI models (Until 1996) and some Forester (Until 1998). The differences between them are the power output which was higher on the WRX STI as it had lighter valves.

For Phase II (Which is the one that actually concern us) I’m going to try to be more precise in the explanation. Compared to the Phase I this engines have a number at the end to describe the features of these engines.

In first place we have the engines with the lowest displacement. These engines were numered: EJ151, EJ152, EJ153 and EJ154 which were offered in the Subaru Impreza from 1993 to 2006. In this case, the higher the number, the higher the torque and the power; they were offered from 96 bhp to 99 bhp. These engines and the EJ16 series were replaced for 2007 by the EL engine series.

Then we have EJ181, EJ182 and EJ183 which came with power outputs from 108 bhp to 118 bhp. These engines were available on the Impreza GC6, Legacy (JDM) and (suprisingly) the Isuzu Aska.

And now they beloved EJ20. Here is when you say: “YEAH! Finally something powerful!”… Sorry for this but no. Not yet. They were numered from EJ202 and EJ204 which were naturally aspirated engines. The first one an SOHC for the Forester, and the second one a DOHC which were installed in some Impreza GC and some Legacy.

Now, finally something that can excite us a bit more: The turbocharged engines!

Let’s begin with the EJ205. This one is available in the WRX and the SF5 Forester. Is such an engine that Subaru haven’t thought of replacing it since 1999. The current WRX model still have the same, and even the SAAB 9-2X Aero brings it!

There is also an EJ207 which was the used for those vehicles with the WRC homologation. This engine reaches higher revs than the previous EJ205.

But this serie has more to offer. In fact there was available a hardcore Twin Turbo version which was installed in some Legacy models.

As you noticed there are many EJ20 engines. which is something that happens with the EJ25. In fact the EJ251, EJ252 and EJ253 are SOHC which offer a maximum power output of 165 Hp. There is also a EJ254 which is Naturally Aspirated.

And the one that we find in the WRX STI nowadays is named EJ257, which is a turbocharged DOHC with 16 valves and dished pistons.

Now that you know this, pick one and swap the engine of your car!

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.