Subaru EJ255 Specifications
| Engine Model: Subaru EJ255 |
| Engine Type: 4-cycle 4-cylinder DOHC 16-valve turbocharged liquid-cooled gasoline |
| Total Displacement: 150 cu.in (2.45 L) |
| Rated Engine Power: 210-265 Hp (157-198 kW) at 5600 rpm |
| Fuel System Type: Multi-point electronic fuel injection |
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000000000000000000000The Subaru EJ255 is a 2.5-liter
turbocharged flat-four engine produced from 2003 through 2014, serving as the
primary turbocharged powerplant for Subaru’s non-STi performance models.
Developed as a higher-displacement successor to the 2.0-liter EJ205, the EJ255
was engineered to deliver improved mid-range torque and everyday driveability
compared to its higher-performance stablemate, the EJ257, while sharing the same
fundamental 2.5-liter architecture. The engine’s horizontally opposed
configuration provides a low center of gravity and inherent balance
characteristics that have defined Subaru’s performance identity.
The EJ255 is constructed entirely from aluminum alloy - cylinder block, cylinder
heads, and crankcase - contributing to reduced overall mass while maintaining
the structural rigidity required for turbocharged operation. The semi-closed
deck block design provides greater cylinder wall support than open-deck
configurations, enhancing durability under boost pressure while allowing
adequate coolant flow around the combustion chambers.
The double overhead camshaft (DOHC) valvetrain incorporates Single Active Valve
Control System (AVCS) on the intake camshafts, allowing for variable intake
valve timing to optimize volumetric efficiency across the operating range. The
timing belt system drives both camshafts and the water pump; this is an
interference engine, and belt failure results in valve-to-piston contact.
Power output varies across applications and model years, ranging from 210 to 265
hp (157 to 198 kW) at 5,600 rpm, with torque spanning 235 to 258 lb-ft (319 to
350 Nm) at 3,600 rpm. The compression ratio ranges from 8.2:1 to 8.4:1 depending
on year and market, calibrated for forced induction with the factory
turbocharger - either a Mitsubishi TD04L in WRX and Forester XT applications or
an IHI VF series turbocharger (VF40, VF46, or VF52) in Legacy GT and Outback XT
configurations.
The intercooler configuration also varies: WRX and Forester XT utilize a
top-mount intercooler with a blow-off valve mounted to the intercooler, while
Legacy GT employs a unique flanged intercooler design that bolts directly to the
turbocharger compressor housing.
The EJ255 operates on a four-stroke gasoline cycle with turbocharged induction
and multi-point fuel injection. The engine utilizes a horizontally opposed
(flat) four-cylinder configuration with a double overhead camshaft (DOHC) and
four valves per cylinder.
Engine Type: Horizontally opposed 4-cylinder, water-cooled, 4-stroke, turbo
gasoline.
Displacement: 2,457 cc (150 cu.in).
Bore: 99.5 mm (3.92 in).
Stroke: 79.0 mm (3.11 in).
Compression Ratio: 8.2:1 to 8.4:1 depending on year and vehicle application.
Firing Order: 1-3-2-4.
Idle Speed: 700 - 750 rpm, electronically controlled.
Maximum Engine Speed: 6,500 rpm with fuel cut-off at 6,800 rpm.
Maximum Power: 157-198 kW (210-265 hp) @ 5,600 rpm.
Maximum Torque: 319-350 Nm (235-258 lb-ft) @ 3,600 rpm.
Fuel System: Sequential multi-point fuel injection with four injectors
positioned in the intake manifold runners.
Aspiration: Turbocharged with air-to-air intercooler (top-mount or front-mount
depending on vehicle).
The cylinder block is constructed from cast aluminum
alloy with a semi-closed deck design. In this configuration, the cylinder bores
are partially supported by the deck surface at the top of the block, with
cast-in bridges between the cylinders that provide additional structural support
while maintaining coolant passages around the combustion chambers. This design
offers greater cylinder wall rigidity than open-deck blocks while avoiding the
cooling limitations of fully closed-deck configurations.
The cylinder bores are integrally cast into the aluminum block with
cast-in-place iron liners. Each liner is centrifugally cast from gray iron and
is permanently bonded to the aluminum block during the casting process. The 99.5
mm bore diameter provides the 2.5-liter displacement when combined with the 79.0
mm stroke.
The crankcase utilizes a two-piece construction with the cylinder block forming
the upper crankcase and a separate aluminum bedplate forming the lower
crankcase. The bedplate incorporates the main bearing supports and is secured to
the cylinder block with multiple bolts, providing superior crankshaft rigidity
compared to conventional main bearing cap designs.
Crankshaft: Forged steel with five main bearings, fully counter-weighted with
eight counterweights. The crankshaft features induction-hardened bearing
surfaces and incorporates a torsional vibration damper at the front end.
Main Bearing Journal Diameter: 60.0 mm (2.36 in)
Connecting Rod Journal Diameter: 52.0 mm (2.05 in)
Connecting Rods: Forged steel with a fracture-split cap design
Piston Material: Cast aluminum alloy with anodized ring grooves. The piston
crown incorporates a dish design to achieve the target compression ratio. Cast
pistons are a known limitation in high-boost applications; the ringlands are
susceptible to cracking under detonation or excessive cylinder pressure. Piston
Cooling: Oil spray jets mounted in the crankcase direct engine oil to the
underside of each piston crown. These jets are calibrated to activate at oil
pressures above 150 kPa (22 psi).
The EJ255 utilizes two separate cylinder heads, one for
each cylinder bank, each manufactured from cast aluminum alloy. The DOHC
configuration places two camshafts in each head - one intake and one exhaust -
operating four valves per cylinder through inverted bucket-type tappets.
Valvetrain: Double overhead camshaft (DOHC) per cylinder bank, with four valves
per cylinder, totaling 16 valves. Single Active Valve Control System (AVCS) is
incorporated on the intake camshafts, allowing for adjustment of intake valve
timing across a range of up to 35 degrees of crankshaft rotation based on engine
speed and load. Hydraulic lash adjusters are not used; valve clearance is
maintained by selecting appropriate tappet thicknesses during service.
Intake Valve Diameter: 34.0 mm (1.34 in)
Exhaust Valve Diameter: 30.0 mm (1.18 in)
Valve Lift (Intake): 9.5 mm (0.374 in)
Valve Lift (Exhaust): 9.5 mm (0.374 in)
Valve Clearance (cold): Intake 0.20 - 0.25 mm (0.008 - 0.010 in); Exhaust 0.25 -
0.30 mm (0.010 - 0.012 in). Valve Seat Material: High-strength sintered alloy
with induction-hardened contact surfaces. Valve Spring Material: High-tensile
steel with a beehive design to reduce reciprocating mass.
Camshaft Drive: Belt-driven system utilizing a toothed rubber timing belt
reinforced with fiberglass cords. The belt drives the water pump and the
camshaft sprockets from a single sprocket on the crankshaft. An automatic
spring-loaded tensioner maintains belt tension. This is an interference engine;
timing belt failure results in valve-to-piston contact.
The fuel system is a sequential multi-point fuel
injection system with individual injectors positioned in the intake manifold
runners immediately upstream of each intake valve. This port injection
configuration provides reliable fuel delivery and resists the carbon deposit
issues associated with direct injection systems.
Fuel Injectors: High-impedance solenoid-type injectors with a flow rate
calibrated to the turbocharged application. Flow rates vary by application, with
Legacy GT and later WRX models utilizing higher-flow injectors than early WRX
applications. Fuel Pressure: 350 - 400 kPa (51 - 58 psi) regulated by a
vacuum-referenced pressure regulator mounted on the fuel rail. Fuel Rail:
Aluminum rail shared across each cylinder bank.
Intake Manifold: Composite resin or cast aluminum construction depending on
vehicle. WRX and Forester XT utilize a top-mount intercooler integrated with the
intake manifold assembly; Legacy GT uses a separate intercooler configuration
with a flanged connection to the turbocharger.
Throttle Body: Electronically controlled drive-by-wire system on later models;
cable-actuated throttle on early applications. Fuel Requirement: Minimum octane
rating of 95 RON (91 AKI) for optimal performance; lower-octane fuel may result
in reduced power output and increased risk of detonation.
The lubrication system is a fully pressurized wet-sump
design with a gear-type oil pump mounted on the front of the engine. The pump is
driven directly by the crankshaft through the timing belt system and
incorporates a pressure relief valve.
Oil Pump Type: Gear-type pump with integrated pressure relief valve. Recommended
Oil Viscosity: 5W-30 or 5W-40 fully synthetic oil meeting API SN or higher
specifications. Synthetic oil is required for turbocharger protection and
high-temperature stability. Oil Capacity (including filter): 4.5 - 5.0 liters
(4.8 - 5.3 qt) depending on oil pan configuration and vehicle application.
Oil Pressure (at idle, warm): 100 - 150 kPa (15 - 22 psi).
Oil Pressure (at 3,000 rpm, warm): 350 - 450 kPa (51 - 65 psi).
Oil Filter Type: Spin-on full-flow filter with integral bypass valve and
anti-drainback valve.
Oil Cooler: Water-to-oil heat exchanger integrated into the oil filter mounting
base on most applications, utilizing engine coolant to stabilize oil
temperatures under sustained turbocharged operation. Oil Pan: Stamped steel with
integrated baffling and a windage tray to reduce oil aeration at high engine
speeds.
Turbocharger Oil Feed: Early models (2005-2009) incorporate a fine-mesh screen
filter within the banjo bolt at the turbocharger oil feed line. This filter is a
known failure point; clogging restricts oil flow to the turbocharger, resulting
in bearing failure.
The cooling system is a pressurized, thermostatically
controlled circuit utilizing a belt-driven centrifugal water pump. The water
pump is driven by the timing belt in this engine configuration, necessitating
replacement during timing belt service.
Water Pump Type: Centrifugal with a mechanical seal, mounted to the front of the
cylinder block and driven by the timing belt. Coolant Type: Ethylene-glycol
based antifreeze meeting Subaru specification, phosphate and silicate-free
formulation. Coolant Capacity (engine and radiator): 6.0 - 6.5 liters (6.3 - 6.9
qt) depending on vehicle model and intercooler configuration. Thermostat:
Wax-type thermostat with an opening temperature of 82 °C (180 °F) and a
full-open temperature of 95 °C (203 °F).
Radiator: Cross-flow aluminum radiator with plastic tanks. Charge Air Cooling:
Air-to-air intercooler - top-mount configuration on WRX and Forester XT,
positioned above the engine; front-mount on select aftermarket applications.
Cooling Fan: Electric fan assembly controlled by engine coolant temperature
sensor and air conditioning system demand.
Timing Drive: Belt-driven system with a toothed rubber
timing belt. The belt drives both camshafts and the water pump. An automatic
spring-loaded tensioner maintains belt tension. The belt must be replaced at
specified intervals; failure results in valve-to-piston contact.
Accessory Drive: Single serpentine belt driving the alternator, power steering
pump, and air conditioning compressor. A spring-loaded automatic tensioner
maintains belt tension.
Turbocharger: Mitsubishi TD04L turbocharger on WRX (2006-2014) and Forester XT
(2004-2013) applications. IHI VF40, VF46, or VF52 turbochargers on Legacy GT and
Outback XT (2005-2012) applications. The turbocharger features a wastegate
controlled by an electronic solenoid valve. Maximum boost pressure ranges from
0.7 to 1.0 bar (10 to 15 psi) depending on application and model year.
Ignition System: Distributorless ignition system with coil-on-plug
configuration. Each cylinder has an individual ignition coil mounted directly
over the spark plug. Ignition timing is controlled by the engine control unit
based on crankshaft position, camshaft position, knock sensor inputs, and engine
load. Spark Plugs: NGK ILFR6B or equivalent iridium. Spark Plug Gap: 0.6 - 0.7
mm (0.024 - 0.028 in).
Engine Management System: Subaru electronic control unit (ECU) with integrated
fuel injection control, ignition timing control, AVCS actuation, boost pressure
control, and diagnostic functions. The ECU utilizes a Mass Air Flow (MAF) sensor
for load detection.
Exhaust System: Cast iron exhaust manifold with unequal-length runners,
contributing to the characteristic Subaru exhaust note. The exhaust system
incorporates a close-coupled catalytic converter in the up-pipe and a second
catalytic converter in the downpipe.
Overall Length: 620 mm (24.4 in)
Overall Width: 680 mm (26.8 in)
Overall Height: 560 mm (22.0 in)
Dry Weight (complete engine): 150 kg (331 lb)
Engine Oil and Filter Change: 5,000 km (3,000 mi) or 6
months for conventional oil; 7,500 km (4,500 mi) for synthetic oil. Turbocharged
operation demands strict adherence to oil change intervals to prevent coking in
the turbocharger bearing housing. Fuel Filter Replacement: 30,000 km (18,000 mi)
or 2 years. Engine Air Filter Element: Replace every 20,000 km (12,000 mi) or
when visibly contaminated. Coolant Replacement: 40,000 km (24,000 mi) or 2
years.
Timing Belt Replacement: 100,000 km (60,000 mi) or 5 years, whichever occurs
first. Failure to replace the belt within this interval risks belt fracture and
consequent valve damage due to the interference design. Water Pump Replacement:
Replaced concurrently with timing belt due to water pump drive by the timing
belt. Valve Clearance Inspection: Every 100,000 km (60,000 mi). Adjustment is
performed by selecting and installing replacement tappets of appropriate
thickness.
Drive Belt Inspection: Every 10,000 km (6,000 mi) for cracks, fraying, glazing,
and proper tension. Drive Belt Replacement: 60,000 km (37,000 mi) or 3 years.
Spark Plug Replacement: 60,000 km (37,000 mi) for iridium plugs. Turbocharger
Oil Feed Banjo Bolt Filter (2005-2009 models): Inspection and removal of the
mesh filter is recommended to prevent turbocharger oil starvation. Many
aftermarket sources recommend removing this filter entirely while maintaining
regular oil change intervals.
Cylinder Head Bolts, Step 1: 30 Nm (22 lb-ft)
Cylinder Head Bolts, Step 2: 60 Nm (44 lb-ft)
Main Bearing Bedplate Bolts, Step 1: 20 Nm (15 lb-ft)
Main Bearing Bedplate Bolts, Step 2: 50 Nm (37 lb-ft)
Connecting Rod Cap Bolts: 30 Nm (22 lb-ft)
Camshaft Bearing Caps: 15 Nm (11 lb-ft)
Camshaft Sprocket Bolts: 80 Nm (59 lb-ft)
Timing Belt Tensioner: 25 Nm (18 lb-ft)
Intake Manifold to Cylinder Head: 20 Nm (15 lb-ft)
Exhaust Manifold to Cylinder Head: 35 Nm (26 lb-ft)
Turbocharger to Exhaust Manifold: 28 Nm (21 lb-ft)
Turbocharger Oil Feed Line: 25 Nm (18 lb-ft)
Oil Pan Bolts: 12 Nm (9 lb-ft)
Valve Cover Bolts: 8 Nm (6 lb-ft)
Spark Plugs: 20 Nm (15 lb-ft)
Crankshaft Pulley Bolt: 180 Nm (133 lb-ft)
Flywheel / Flexplate Bolts: 70 Nm (52 lb-ft)
Engine Mount Brackets to Block: 45 Nm (33 lb-ft)
The EJ255 was widely utilized across Subaru’s North
American and Australian performance model lines from 2003 through 2014.
Subaru Impreza WRX (2006 - 2014): The GD-chassis (2006-2007) and GR-chassis
(2008-2014) Impreza WRX received the EJ255 as the standard turbocharged engine,
replacing the earlier 2.0-liter EJ205. Power output varied by year: 2006-2007
models produced 230 hp (172 kW) with 235 lb-ft (319 Nm); 2008-2014 models
produced 265 hp (198 kW) with 258 lb-ft (350 Nm). The engine was mounted
longitudinally with Subaru’s symmetrical all-wheel-drive system and was offered
with a five-speed manual transmission.
Subaru Forester XT (2004 - 2013): The SG-chassis (2004-2008) and SH-chassis
(2009-2013) Forester XT received the EJ255 with a Mitsubishi TD04L turbocharger.
Power output ranged from 210 hp (157 kW) in early models to 224 hp (167 kW) in
later versions. The Forester XT utilized a top-mount intercooler and was offered
with either a four-speed automatic or five-speed manual transmission depending
on model year and market.
Subaru Legacy GT (2005 - 2012): The fourth-generation (BL/BP, 2005-2009) and
fifth-generation (BM/BR, 2010-2012) Legacy GT received the EJ255 with IHI VF40,
VF46, or VF52 turbochargers depending on year. Power output was 250 hp (186 kW)
with 250 lb-ft (339 Nm) in manual transmission models; automatic models received
a slightly lower torque rating. The Legacy GT utilized a unique intercooler
configuration that bolted directly to the turbocharger compressor housing.
Subaru Outback XT (2005 - 2009): The Outback XT, based on the Legacy platform,
received the EJ255 with the same IHI turbocharger and intercooler configuration
as the Legacy GT. Power output was 250 hp (186 kW) with 250 lb-ft (339 Nm). The
Outback XT was offered with either a five-speed manual or five-speed automatic
transmission with Subaru’s all-wheel-drive system.
Subaru Baja Turbo (2004 - 2006): The Baja light-duty pickup received the EJ255
as the turbocharged engine option for the 2004 through 2006 model years. Power
output was 210 hp (157 kW) with 235 lb-ft (319 Nm). The Baja Turbo utilized the
same TD04L turbocharger and top-mount intercooler configuration as the Forester
XT.
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