FEATURE STORIES

Our Favorite Engines: The Subaru EJ25

Our Favorite Engines: The Subaru EJ25 image

Aurick Go / Manufacturer Press, AutoIndustriya.com | April 26, 2018 17:02

The ups and downs of Subaru’s signature boxer motor

With their widespread popularity, practical packaging, and rally-bred heritage, a Subaru Impreza WRX or even an STI has become quite the common sight on Manila’s streets. Conveniently blending a four door or hatchback body with symmetrical AWD and their iconic turbo flat-four boxer engine, it’s safe to say the WRX STI has become the weapon of choice for most folks that want speed mixed into their daily commute.

Our Favorite Engines: The Subaru EJ25

But while aspiring to own one of these rally-bred saloons is one thing, owning and maintaining its EJ25 powerplant can be quite a chore if it’s left unattended. To start off our Engine Series, we will talk you through the basics of owning a Subaru with an EJ25 turbo motor, how it drives, and what other issues you could run into during your ownership. And while the following information may be somewhat general and sweeping, I can give enough credit to them since I’ve owned and driven a 2008 GH8 Impreza WRX for about 6 years – and have had my fair share of fun and issues with that car. And with that, let’s first go over a quick history of Subaru’s most popular boxer motor.

Any Subaru fan will tell you that the EJ25 is part of the ‘EJ’ family of engines. Subaru engine nomenclature usually indicates the first 2 letters as the ‘engine family’ designation while the last two digits indicate displacement. An engine family is a series of engines with relatively the same structure but come in different sizes and displacements. In this case, and as stated above, the EJ25 is a 2.5L flat-four boxer engine belonging to the EJ family of engines. The EJ series first started in 1989, but the EJ25 itself first materialized sometime in 1996 with a naturally aspirated version having been released for the Subaru Legacy in the US. The EJ25 we’ve come to know actually started becoming popular since the first Impreza WRX STIs (GDB Chassis) sold in the US came with these motors in the mid 2000’s.

Our Favorite Engines: The Subaru EJ25

Considering its rally-bred origins, the EJ25 lends itself well to both city driving and a spirited run thanks to one key attribute: Response. With about 230-300 PS on tap paired with roughly 300 Nm of torque, the WRX STI can pick up the pace fairly quickly thanks to the EJ25’s fat mid-range torque – not to mention the tiny turbocharger hanging off the side to help it along. That said, driving a Subaru has since been associated with quick pick-up and solid launches thanks to its ability to get off the line in brisk fashion. The downside of this is all that grunt in the mid-range means the EJ25 doesn’t have power in the upper rev ranges. In stock form the EJ25 has a rev limit of about 6,500rpm but when looking at dyno sheets the motor will usually stop making power at 5,500rpm – meaning it may be better to shift earlier to stay on the powerband.

With the layout of the engine itself being flat, the flat-four boxer layout gives Subarus a sure-footed feel on the road. With the center of gravity being lower than in a conventional inline-four, Subarus tend to feel more stable when cornering instead of feeling like it will topple over. While this is certainly an advantage in racing, driving it on the street will still bring out the confidence in its drivers considering how the car stays balanced through the corners.

Our Favorite Engines: The Subaru EJ25

But while driving a Subaru has its advantages behind the wheel, the maintenance end of things can become quite costly if you find yourself unlucky.  For starters, the flat layout means the spark plugs are on opposite ends of the engine instead of being on top. Sandwiched between the strut towers, usually the servicing of spark plugs in a boxer motor would entail having to bring the motor down slightly just to change them. Some expert mechanics can perform this with minimal removal of parts and very deft hands, but the usual case for changing plugs is a laborous affair for boxer engines.

While the plugs can be hard to reach, the EJ25 suffers from even bigger issues that have yet to have definite, clear cut solutions. Among Subaru folk, the words ‘ringland failure’ or ‘spun con-rod bearings’ are pretty much a common way of saying ‘your engine’s dead.’ A ringland failure happens when the seat of the piston ring deforms on the piston – thereby losing compression since the rings won’t seat properly. On the other hand, a spun connecting rod bearing means the connecting rod pushing the piston will spin the wrong way during the combustion cycle – meaning your pistons won’t compress anything since it’s not in sync. There are many arguments as to why this happens, but whether it’s by negligence in modification or just simply the luck of the draw on a stock motor (or lack thereof), the EJ25 is prone to these fatal issues. My WRX actually suffered from rod-bearing failure at 2000 kms bone stock, thankfully warranty changed the motor out with no fuss.

Our Favorite Engines: The Subaru EJ25

With these critical issues on Subaru’s EJ25, it is then imperative that you go about modifying it with proper research and consultation. For starters, you should talk to people who know what they’ve been doing with these motors and have had strings of good reliability with them. Chances are they’ll tell you to focus on reliability first before adding power. Things like a good tune, upgraded cooling components like radiators, oil coolers, and power steering coolers may go a long way towards preserving your motor. Some sources point out that lubrication in an EJ25 is the cause of concern for all its problems, so looking at improving that issue in the engine may be well worth the look as well.

As is the case with most performance engines, the Subaru EJ25 is nowhere near perfect and has its fair share of issues. With all of its imperfections studied and properly sorted out however, the EJ25 can prove to be a reliable engine to enjoy performance driving with. At the end of the day, building a car really is just all a matter of doing your research and finding the right people to build your motor for you.