Subaru EJ25 Engine 2.5L Turbo
The Subaru EJ25 is a 2.5-liter, turbocharged flat-4 (boxer) engine that represents the pinnacle of Subaru's EJ-series performance. Introduced in the early 2000s, the EJ25 powered the most iconic Subaru performance models including the USDM WRX STI, Forester XT, Legacy GT, and Outback XT. With 2.5L of displacement providing significantly more low-end and mid-range torque than the EJ20, the EJ25 became the preferred choice for enthusiasts seeking daily drivability combined with high-horsepower potential.
Parameter | Value |
|---|---|
Engine Code | EJ25 (various: EJ255, EJ257, EJ25D, EJ251, EJ253, EJ254) |
Configuration | Flat-4 (Boxer / Horizontally Opposed) |
Displacement | 2,457 cc (2.5L) |
Bore x Stroke | 99.5 mm x 79.0 mm (Oversquare design) |
Cylinder Block Material | Aluminum (open deck on non-turbo / semi-closed deck on turbo STI) |
Cylinder Head Material | Aluminum |
Valvetrain | DOHC, 4 valves per cylinder (turbo) / SOHC (naturally aspirated) |
Compression Ratio | 8.2:1 – 10.0:1 (depending on variant) |
Fuel System | Multi-Point Electronic Fuel Injection (MPFI) |
Ignition System | Coil-on-plug (distributorless) with wasted spark |
Engine Weight (Dry) | 149-159 kg (328-350 lbs) |
Redline | 6,500 – 7,000 RPM (depending on variant) |
Variant | Application | Power | Torque | Key Features |
|---|---|---|---|---|
EJ257 (USDM STI) | Impreza WRX STI (GD/GR/GV) 2004-2021 | 293-310 hp @ 6,000 rpm | 290-310 lb-ft @ 4,000 rpm | Semi-closed deck, forged pistons (later years), AVCS |
EJ255 (WRX/LGT/FXT) | Impreza WRX (GD/GR), Legacy GT, Forester XT 2005-2014 | 224-265 hp @ 5,200-6,000 rpm | 226-260 lb-ft @ 3,600 rpm | Open deck, cast pistons, AVCS |
EJ25D (Early DOHC) | Subaru Legacy/Outback 1996-1999 | 165 hp @ 6,000 rpm | 162 lb-ft @ 4,000 rpm | DOHC, naturally aspirated, known for head gasket issues |
EJ251 | Subaru Impreza RS/Forester/Legacy 1999-2004 | 165 hp @ 5,600 rpm | 166 lb-ft @ 4,000 rpm | SOHC, naturally aspirated |
EJ253 | Subaru Impreza/Forester/Legacy 2005-2011 | 170-173 hp @ 5,600 rpm | 170 lb-ft @ 4,400 rpm | SOHC, improved head gasket design, AVLS (variable lift) |
EJ254 (JDM) | Subaru Legacy B4 (BE/BH) 1998-2003 | 217 hp @ 7,000 rpm | 206 lb-ft @ 5,600 rpm | DOHC turbo, twin-turbo configuration (JDM only) |
Boxer (Horizontally Opposed) Configuration: Pistons move horizontally (180° apart), creating a naturally low center of gravity for superior handling and balanced weight distribution.
Semi-Closed Deck Block (EJ257 only): Cast-in reinforcement ribs around cylinder bores provide strength for high boost (400-500+ whp capable on stock block).
AVCS (Active Valve Control System): Subaru's variable valve timing system on intake cams (EJ255/EJ257) improves low-end torque, throttle response, and fuel efficiency.
AVLS (Active Valve Lift System): Variable valve lift on naturally aspirated EJ253 variants (not performance-oriented).
2.5L Displacement Advantage: 25% more displacement than the EJ20 provides significantly more low-end torque for daily driving and faster spool on turbochargers.
Sodium-Filled Exhaust Valves (EJ257): Improved heat dissipation for high-performance durability.
Forged Pistons (EJ257 late years): Late-model EJ257 variants feature factory forged pistons for improved reliability.
Cast Iron Cylinder Liners: Press-fit liners provide wear resistance and allow for overboring.
DOHC 16-Valve Cylinder Head (Turbo variants): High-flow cross-flow design for forced induction applications.
Variant | Donor Vehicle | Years | Key Notes |
|---|---|---|---|
EJ257 | Impreza WRX STI (GD/GR/GV/VA) | 2004-2021 | Most desirable. Semi-closed deck. Forged pistons (2006+). AVCS. |
EJ255 | Impreza WRX (GD/GR) | 2005-2014 | Open deck. Cast pistons. Common and affordable. |
EJ255 | Legacy GT (BP/BL) | 2005-2009 | Same as WRX EJ255. Popular for swaps. |
EJ255 | Forester XT (SG/SH) | 2004-2013 | Same as WRX EJ255. Direct fit for Forester. |
EJ255 | Outback XT (BP/BL) | 2005-2009 | Same as WRX EJ255. Rare but excellent donor. |
EJ253 | Impreza 2.5i / Forester / Legacy | 2005-2011 | Naturally aspirated. Not for performance builds. |
EJ25D | Legacy / Outback | 1996-1999 | Early DOHC NA. Avoid for swaps. |
EJ254 (JDM) | Legacy B4 RSK (BE/BH) | 1998-2003 | JDM twin-turbo. Complex vacuum system. |
1x Subaru EJ25 Longblock (Cylinder head + engine block)
1x Intake Manifold (with or without TGV deletes – specify)
1x Turbocharger (IHI VF series – VF39, VF43, VF48, VF52 depending on variant)
1x Exhaust Manifold (Equal or unequal length)
1x Top-Mount Intercooler (TMIC) – if included (STI or WRX)
1x Wiring Harness (if included – specify donor vehicle)
Injectors, alternator, starter, and ECU.