5250 High Performance Dyno Shop Blog

Subaru Engines | EJ vs. FA motors - what you need to know

[fa icon="calendar"] Jan 5, 2017 11:16:00 AM / by Mike Wiener

Subaru FA motorsBuilding power with Subaru’s newest motor design, the FA series. This is found in all of the turbo models except the STi.

Vehicles with this motor appeared in 2014 in the Forester and in 2015 with the WRX.

This is a new engine design coming from the EJ series with the main differences being displacement, compression ratio, and having direct fuel injection.

No, this isn't a post about getting more power, it is one for understanding the basic needs of this motor vs. previous Turbo Subarus.

Even though these motors have only 2 liters instead of 2.5, they have a greater power potential then the outgoing motor. With that comes a requirement of deeper understanding for this engine, or you will blow it up.

People who own vehicles with this engine family are beginning to accumulate miles and require preventative maintenance. The first major service item to hit are the spark plugs at 60,000 miles.

This is the change interval Subaru has specified, but we are seeing some cars needing new plugs as early as 30,000 miles. Why?

A common issue with the new engine platform is the increased tendency to knock. While the EJ motors remain sensitive to knock conditions and tuners do everything in their power to prevent detonation, the FA motors are even more sensitive and the challenges of direct injection have made avoiding knock much harder. With cylinder conditions on the edge of pre-ignition, spark plugs tend to erode faster than normal.

So what's the big deal? Every car needs new plugs every so often. Well, the FA engine uses a different style spark plug than the EJ engines. This wouldn't be a big deal, except there are only a few options for spark plug choices.

With the EJ engine, you can choose multiple styles of plug type in various temperature ranges. We put 1-step colder plugs in almost every EJ engine that comes through our shop. So this is what we would like to do with the FA series... except those options aren't available.

The most readily available spark plug is the Subaru branded plug from the dealership. These are easy to find, but the dealership wants $24 per spark plug. They’re not that special.

If money is of value to you and you can wait a day or two, purchase the NGK brand spark plug. It's actually the same plug you'll find in the Subaru box, but since it doesn't say Subaru on the side, it only costs $15. So that saves you a few dollars per plug, but it's the same heat range as stock.

Subaru FA turbo motorsThis is where it gets scary fast. If you plan on making big power, you need colder plugs. NGK only has one spark plug in their catalog that fits the FA motor and is a colder heat range. The plug is from their racing line, is 2 steps colder than stock, but costs $146... each. You read that right, as of today that is Five Hundred and Eighty-Four dollars for a set of spark plugs. No, we are not making this up.

This should only be a temporary problem as the FA series is so new, there isn't much aftermarket support. In the next few months, expect to find more cost effective spark plug options from NGK and other manufacturers.

In the meantime, make sure your tune isn't too hot and detonating lightly or you will end up needing a new motor.

Ready for more power already? Set up an appt to stop by and discuss your needs / wants. 

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Topics: Subaru Horsepower

Mike Wiener

Written by Mike Wiener