The Subaru EJ255 is a 2,457 cc, flat-four petrol engine produced between 2004 and 2012. It features a DOHC 16-valve configuration with multi-point fuel injection (MPFI) and turbocharging, delivering 169 kW (230 PS) in standard applications. Developed as part of Subaru's high-performance EJ series, it was engineered for the Legacy GT and Impreza WRX platforms, combining strong mid-range torque with rally-bred reliability.
Fitted to models such as the Legacy BP/BH and Impreza GR/GV, the EJ255 was designed for enthusiasts seeking balanced performance and all-weather capability. Emissions compliance was achieved through oxygen sensor feedback control and catalytic converters, allowing most units to meet U.S. EPA Tier 2 Bin 5 standards, with certain European exports meeting Euro 4.
One documented reliability concern is head gasket degradation under prolonged thermal stress, highlighted in Subaru Service Information Bulletin SSB-05-028. This issue is often associated with coolant system neglect or aggressive driving cycles. In 2006, Subaru revised the cylinder head bolt torque sequence and introduced updated gasket materials to improve sealing integrity.
Production years 2004–2005 meet U.S. EPA Tier 2 Bin 5; 2006–2012 models comply with enhanced emissions protocols (VCA UK Type Approval #VCA/EMS/2011).
The Subaru EJ255 is a 2,457 cc flat-four turbocharged engine engineered for performance applications (2004–2012). It combines Subaru's horizontally-opposed layout with single turbocharging to deliver strong low-to-mid RPM torque and responsive power delivery. Designed primarily for North American and Japanese markets, it balances motorsport-derived performance with daily drivability.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 2,457 cc | |
| Fuel type | Petrol | |
| Configuration | Flat-4, DOHC, 16-valve | |
| Aspiration | Turbocharged | |
| Bore × stroke | 99.5 mm × 79.0 mm | |
| Power output | 169 kW (230 PS) @ 5,600 rpm | |
| Torque | 320 Nm @ 2,000–4,800 rpm | |
| Fuel system | Multi-point fuel injection (MPFI) | |
| Emissions standard | U.S. EPA Tier 2 Bin 5 (pre-2006); Enhanced protocols (2006-2012) | |
| Compression ratio | 8.4:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | IHI VF44 (cast turbine housing) | |
| Timing system | Belt-driven (front-mounted) | |
| Oil type | SAE 5W-30 (API SM) | |
| Dry weight | 145 kg |
The turbocharged flat-four layout provides excellent balance and low center of gravity ideal for all-wheel-drive dynamics but requires strict maintenance to sustain longevity. SAE 5W-30 oil meeting API SM specifications is recommended for optimal lifter and camshaft lubrication. Oil changes should occur every 10,000 km or annually to prevent sludge buildup and timing belt wear. The interference design means valve damage will occur if the timing belt fails. Valve clearance adjustments are required every 30,000 km using feeler gauges per factory procedure. Turbo operation demands regular inspection of intercooler piping and blow-off valve function to maintain boost pressure stability.
Oil Specs: Requires API SM-rated 5W-30 oil (Subaru SIB SSB-05-028). Compatible with ILSAC GF-4 requirements.
Emissions: Enhanced emissions certification applies to post-2006 models only (VCA Type Approval #VCA/EMS/2011). Pre-2006 variants meet U.S. EPA Tier 2 Bin 5.
Power Ratings: Measured under JIS D 1001 standards. Output achieved with 91 RON fuel and optimal ignition timing (Subaru TIS Doc. A25PERF).
Subaru Technical Information System (TIS): Docs A25EJ, A25FUEL, A25TIMING
VCA Type Approval Database (VCA/EMS/2011)
JIS D 1001: Internal combustion engine — Test code
The Subaru EJ255 was used across Subaru's Legacy GT and Impreza WRX platforms with longitudinal mounting and symmetrical all-wheel drive. This engine received platform-specific adaptations-reinforced block castings in the Legacy BH and revised intake manifolds in the Impreza GR-and from 2006 the updated Legacy BP Facelift models adopted improved head gaskets and oil squirters, creating interchange limits. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped horizontally on the front-left cylinder block near the exhaust manifold (Subaru TIS A25ID01). The 4th digit of the VIN indicates engine family ('E' for EJ series). Pre-2006 models have silver valve covers with ribbed rocker housings; post-2006 units use black valve covers with revised fastener layouts. Critical differentiation from EJ257: EJ255 has IHI VF44 turbo and different ECU calibration. Service parts require production date verification - head gaskets and oil pans for pre-2006 models are incompatible with later revisions due to internal cooling passage updates (Subaru SIB SSB-05-028).
The EJ255's primary reliability risk is head gasket failure on high-mileage engines, with elevated incidence in vehicles subjected to sustained high-load operation. Internal Subaru engineering reports noted increased gasket blowout rates beyond 150,000 km, while UK DVSA field data shows a notable share of coolant contamination failures linked to degraded seals. Extended track use and delayed maintenance increase thermal stress, making coolant quality and flush intervals critical.
Analysis derived from Subaru technical bulletins (2004-2012) and UK DVSA failure statistics (1995-2023). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about SUBARU EJ255.
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