Subaru does things differently, and the engine bay is where it shows the most. Instead of the inline four or V6 layouts most brands use, Subaru builds boxer engines across nearly its entire lineup. It is one of the few automakers still committed to this layout at scale, and it shapes everything from how the car handles to how a swap engine bolts in. This guide breaks down the EJ, FA, and FB families, what sets them apart, and which one makes sense for your build or your next used car purchase.

What Is a Subaru Boxer Engine?

Flat-Four Layout and Why Subaru Uses It

A boxer engine lays the cylinders flat and horizontal instead of upright like a normal inline engine, or angled like a V engine. The pistons move side to side in pairs, punching outward like a boxer throwing jabs, which is where the name comes from. This layout keeps the engine's center of gravity low, which helps handling, and the opposing pistons cancel out a lot of vibration naturally.

Is a Subaru Engine a Toyota Engine?

This question comes up a lot because Subaru and Toyota have a business relationship, with Toyota holding a stake in Subaru and the two companies co-developing the BRZ and Toyota 86. But no, a Subaru boxer engine is not a Toyota engine. Subaru designs and builds its own boxer engines, including the FA20 found in the BRZ, even though Toyota badges and sells its own version of that same car.

The EJ Family

EJ20 and EJ207

The EJ20 is the classic Subaru turbo engine, most associated with the WRX and STi in various markets. The EJ207 is a Japanese market spec version known for strong turbo response and a devoted following among import enthusiasts. Even today, it remains one of the most requested engines for anyone building an old school WRX or STi.

EJ25, EJ255 and EJ257

The EJ25 bumped displacement up to 2.5L, with the EJ255 and EJ257 representing turbocharged versions found in later WRX and STi models. These larger displacement EJ engines generally offer more low end torque than the EJ20, which some drivers prefer for everyday driving and towing.

Closed Deck vs Semi-Closed Deck

Here is a detail that matters if you plan to push power. Some EJ blocks use a closed deck design, which is stronger and better suited to high boost builds. Others use a semi-closed deck, which is a bit more prone to cylinder wall movement under heavy boost. Knowing which deck design your block has changes how far you can safely push it.

The Head Gasket Reputation

The EJ25, in particular, earned a reputation for head gasket failures, especially in earlier production years. Subaru made changes over time to improve this, but it remains one of the first things experienced buyers check on a used EJ25.

The FA Family

FA20 (BRZ and 86)

The FA20 is a naturally aspirated 2.0L boxer built for the BRZ and Toyota 86. It favors high revving response over low end torque, matching the lightweight, balanced nature of those cars.

FA20DIT (WRX)

The FA20DIT is the turbocharged version used in the WRX. It shares its basic architecture with the naturally aspirated FA20 but adds direct injection and forced induction for a big jump in power over the older EJ based WRX.

FA24

The FA24 is a larger 2.4L boxer used in more recent Subaru models. It offers more displacement than the FA20 while keeping the same general design philosophy of a lighter, more efficient boxer engine.

D-4S Dual Injection

Some FA engines use D-4S, a dual injection system combining both direct and port injection. This setup helps balance performance and fuel efficiency better than direct injection alone, while also reducing carbon build-up issues that pure direct injection engines can suffer from over time.

The FB Family

FB25 and Where It Appears

The FB25 is a naturally aspirated 2.5L boxer found in models like the Legacy and Forester. It is built more for everyday reliability and torque than outright performance, making it a common choice for buyers who want a capable, low maintenance daily driver rather than a project car. It does not carry the same swap culture reputation as the EJ or FA, but it quietly does its job well over hundreds of thousands of miles.

Which Subaru Engine Is the Best?

Best for Reliability

The FB25 and later production EJ25 units tend to offer the most trouble free ownership experience, especially when maintained on schedule with quality oil and coolant.

Best for Boost

The EJ20 and EJ25 turbo variants, along with the FA20DIT, all respond well to boost increases thanks to a long history of aftermarket support and known tuning paths.

Best Value Replacement

Known Subaru Engine Failures and What Causes Them

Ringland Failure

Ringland failure happens when the piston ring lands crack under too much boost or heat, usually from aggressive tuning without proper supporting mods. It is more common on engines pushed well past stock power without upgrading fueling and cooling to match. Running a safe tune with a proper air to fuel ratio goes a long way toward avoiding this altogether.

Spun Bearings and Rod Knock

Spun bearings often trace back to oil starvation, whether from low oil levels, poor maintenance, or aggressive driving before an engine is fully warmed up. Once you hear rod knock, the damage is usually already done.

Head Gaskets on the EJ25

As mentioned earlier, the EJ25 has a known head gasket weakness. Coolant loss without a visible leak, or a sweet smell from the exhaust, are both signs worth investigating early before the problem gets worse.

What to Inspect Before You Buy

• Check for head gasket related coolant loss on EJ25 units

• Inspect turbo seals for oil leaks on boosted engines

• Ask about tuning history and boost levels on modified units

• Confirm the exact engine code matches your chassis

Matching the Transmission

Subaru builds both manual and automatic transmissions to match its boxer engines, and getting this pairing right matters as much as the engine itself. If you are comparing manual options, our STi 6-speed vs WRX 5-speed breakdown covers the differences in strength and gearing between the two.

What a Subaru Engine Costs in 2026

Pricing depends on the engine family, mileage, and whether you need just the block or a full engine and transmission package. An FA20 engine for sale generally costs less than a comparable EJ257, partly due to differences in demand and production numbers. JDM imports remain one of the more budget friendly ways to source a low-mileage unit, especially for older EJ20 and EJ25 variants that are getting harder to find domestically in good condition.

Frequently Asked Questions

What kind of engine is in a Subaru?

Most Subaru models use a horizontally opposed boxer engine, either naturally aspirated or turbocharged depending on the trim.

Is Subaru a Toyota engine?

No. Subaru designs and builds its own boxer engines. Toyota and Subaru share the BRZ and 86 platform, but the engines came from Subaru.

Which Subaru has a 2.5L engine?

Models like the Legacy, Forester, and various WRX and STi trims have used 2.5L boxer engines across the EJ and FB families.

Which Subaru engine is the best?

It depends on your goal. For reliability, the FB25 is hard to beat. For boost potential and aftermarket support, the EJ series and FA20DIT remain the top picks among enthusiasts.

Looking to build or replace a Subaru engine the right way? Browse JDM Subaru engines and JDM Subaru transmissions at JDM Florida. Check out our full EJ20 vs EJ25 comparison, or read about the most reliable JDM engines before starting your build. For a step by step walkthrough, see our guide on installing a JDM engine. Click here for current stock, or read more on our blog.