Subaru WRX Replacement Engine Guide
The WRX uses a different engine from the standard Impreza, and the STI uses a different engine from the WRX. Getting this wrong is the most expensive Subaru mistake.
The Subaru WRX is one of the most commonly replaced performance vehicles in the Phoenix market, and one of the most specific when it comes to engine identification. Unlike most vehicles where the trim determines the engine within a family, the WRX uses entirely different engine families from the standard Impreza.
The WRX and STI each use turbocharged flat-four engines that are specific to those models. The standard Impreza uses a naturally aspirated EJ25 or, in later models, an FA20 or FB25. These are not interchangeable, and confusing them is the starting point for expensive problems.
This guide covers the WRX engine families, the differences from the standard Impreza, and the specific verification steps.
WRX engines by generation
| Generation | Years | WRX engine | STI engine | Key notes |
|---|---|---|---|---|
| Second (GD) | 2002-2007 | EJ205 | EJ257 | EJ205 is a 2.0 turbo. EJ257 is a 2.5 turbo. Different displacement, different internals. |
| Third (GR/GV) | 2008-2014 | EJ255 | EJ257 | WRX moves to 2.5 turbo. EJ255 and EJ257 are different engines. |
| Fourth (VA) | 2015-2021 | FA20DIT | EJ257 | WRX switches to FA20 direct-injection turbo. STI keeps the EJ257. |
| Fifth (VB) | 2022-2024 | FA24 | None | STI discontinued. FA24 is a 2.4 litre turbo. |
WRX vs STI vs standard Impreza
The three models share a body shell but use different engines, different transmissions, different differentials and different suspension. The engine is the most consequential difference for replacement purposes.
The standard Impreza uses a naturally aspirated EJ25 (or FB25/FA20 in later models). The WRX adds a turbocharger and uses a different engine code (EJ205, EJ255 or FA20DIT depending on generation). The STI uses a higher-output turbocharged engine (EJ257) with different internals, different fuel system requirements and different engine management.
The EJ255 (WRX) and EJ257 (STI) are both 2.5 litre turbocharged flat-fours, but they are not the same engine. The compression ratio, the turbocharger, the fuel injectors, the intercooler piping and the engine management all differ. An EJ257 in a WRX is an upgrade, not a like-for-like replacement, and it requires supporting changes.
The head gasket question
Subaru EJ-series engines, both turbo and naturally aspirated, have a well-documented tendency toward head gasket failure. On the WRX, this manifests differently than on the standard Impreza: the turbo engines tend to leak externally or into the cooling system rather than into the oil passages.
When sourcing an EJ255 or EJ257 replacement, ask about the head gasket history of the donor engine. An engine that has had the head gaskets replaced with updated multi-layer steel (MLS) gaskets is a better buy than one with the original gaskets, because the failure is likely to recur.
The FA20DIT and FA24 in the fourth and fifth generation WRX use a different head gasket design and are not subject to the same issue.
What to verify before ordering
- WRX or STI. They use different engines. Confirm the specific model.
- The exact engine code. EJ205 vs EJ255 vs FA20DIT vs EJ257. Each is a specific part.
- Transmission type. The WRX was available with both manual and CVT in some generations. The STI is manual only.
- Turbocharger condition. On a replacement turbocharged engine, the turbo's condition is a significant value factor.
- Head gasket history. On EJ-series engines, ask whether the gaskets have been replaced with MLS units.
- Intercooler and intake configuration. The WRX and STI have different intercooler setups, and the intake piping differs.
Common questions
Can I use a standard Impreza engine in my WRX?
No. The standard Impreza engine is naturally aspirated and lacks the turbocharger, the intercooler, the fuel system upgrades and the engine management that the WRX requires. It would not produce the expected power and would likely not run correctly with the WRX's engine management.
What is the difference between the EJ255 and EJ257?
Both are 2.5 litre turbocharged flat-four engines, but the EJ257 (STI) has a higher compression ratio, a larger turbocharger, different fuel injectors, a different intercooler and different engine management. They are not directly interchangeable without supporting changes.
Are head gaskets a problem on WRX engines?
On the EJ-series engines (EJ205, EJ255, EJ257), head gasket failure is a known issue, though it manifests differently than on the naturally aspirated EJ25. The FA20DIT and FA24 are not subject to the same problem. When sourcing an EJ replacement, ask whether the gaskets have been updated to MLS units.
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