Subaru EJ20TT Specifications
| Engine Model: Subaru EJ20TT |
| Engine Type: 4-cycle 4-cylinder DOHC 16-valve turbocharged liquid-cooled gasoline |
| Total Displacement: 121.9 cu.in (1.99 L) |
| Rated Engine Power: 276 Hp (206 kW) at 6500 rpm |
| Fuel System Type: Multi-point electronic fuel injection |
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The Subaru EJ20TT is a 2.0-liter, horizontally opposed
four-cylinder engine featuring a sequential twin-turbocharged system. Produced
between 1994 and 2005, this engine was developed for smooth power delivery and
reduced turbo lag, primarily for the Japanese Domestic Market (JDM). This engine
represented Subaru's approach to forced induction in the performance-oriented
Legacy and Liberty models, employing a sophisticated sequential turbocharging
arrangement to provide responsive power across the entire engine speed range.
The complex induction system distinguished this engine family from the
single-turbo EJ20 variants found in the Impreza WRX.
The EJ20TT engine is recognized for its unique sequential twin-turbo
architecture, which combines a small primary turbocharger for low-rpm response
with a larger secondary turbocharger that engages at higher engine speeds. This
arrangement delivers a broad torque curve with minimal lag, characteristic of
larger-displacement engines. The horizontally opposed (boxer) configuration
provides a low center of gravity and inherent balance, contributing to the
handling characteristics of the vehicles in which it was installed.
The engine's evolution through multiple iterations - EJ20H, EJ20R, EJ206, and
EJ208 - reflected continuous refinement in boost control, valvetrain durability,
and emissions compliance. The interference valvetrain design mandates strict
adherence to timing belt replacement intervals, as belt failure results in
valve-to-piston contact. The complex induction plumbing, including the
sequential switching system and intercooler configurations, presents unique
service considerations compared to single-turbo Subaru engines.
Engine Type: Horizontally opposed 4-cylinder (boxer), 4-cycle, turbocharged
gasoline.
Displacement: 1,998 cc (121.9 cu.in), equivalent to 2.0 L.
Valvetrain: DOHC, 16 valves with bucket-type tappets and shim adjustment.
Bore: 92.0 mm (3.62 in).
Stroke: 75.0 mm (2.95 in).
Firing Order: 1-3-2-4.
Fuel System: Multi-point sequential fuel injection.
EJ20H (1993-1998)
Compression Ratio: 8.5:1 for automatic transmission variants.
Compression Ratio: 8.8:1 for manual transmission variants.
Maximum Power: 250-260 PS (184-191 kW, 247-256 hp) @ 6,500 rpm.
Maximum Torque: 306-319 Nm (226-235 lb-ft) @ 4,000-5,000 rpm.
Applications: Legacy BD5/BG5 RS and GT models.
EJ20R (1996-1998)
Compression Ratio: 8.5:1.
Maximum Power: 280 PS (206 kW, 276 hp) @ 6,500 rpm.
Maximum Torque: 343 Nm (253 lb-ft) @ 5,000 rpm.
Applications: Legacy BD5/BG5 Revision B and C manual transmission.
EJ206 (1998-2003)
Compression Ratio: 9.0:1.
Maximum Power: 255-260 PS (188-191 kW, 251-256 hp) @ 6,500 rpm.
Maximum Torque: 319 Nm (235 lb-ft) @ 4,800 rpm.
Applications: Legacy BE5/BH5 automatic transmission variants.
EJ208 (1998-2003)
Compression Ratio: 9.0:1.
Maximum Power: 280 PS (206 kW, 276 hp) @ 6,500-7,000 rpm.
Maximum Torque: 343 Nm (253 lb-ft) @ 5,000 rpm.
Applications: Legacy BE5/BH5 B4 and GT-B manual transmission.
The cylinder block is constructed from cast aluminum
alloy using the closed-deck design in early variants (EJ20H, EJ20R) and
transitioning to a semi-closed deck in Phase-II variants (EJ206, EJ208). The
horizontally opposed configuration places the cylinders in two banks oriented
180 degrees apart, creating a low profile and inherent primary balance without
requiring balance shafts.
The block features cast-iron cylinder liners pressed into the aluminum casting
to provide a durable wear surface for the piston rings. The crankcase is split
at the crankshaft centerline, with the block incorporating integrated main
bearing caps. The engine utilizes a forged steel crankshaft with five main
bearings, providing the strength required for turbocharged operation. Piston
cooling oil jets are integrated into the block, directing oil to the underside
of each piston crown.
The cylinder heads are manufactured from aluminum
alloy, with separate castings for the left and right banks. Each head houses the
DOHC arrangement with four valves per cylinder. The combustion chambers feature
a pent-roof design optimized for the horizontally opposed architecture. Intake
valves measure 34.0 mm (1.34 in) in diameter, while exhaust valves measure 31.0
mm (1.22 in).
The valvetrain utilizes bucket-type tappets with shim-under-bucket design,
requiring periodic valve clearance inspection and shim replacement for
adjustment. The camshafts are driven by a single timing belt that routes around
the crankshaft sprocket and both camshaft sprockets on each cylinder head. The
intake and exhaust camshafts on each bank feature variable valve timing on later
Phase-II variants (EJ206 and EJ208), with hydraulic actuators adjusting intake
camshaft phase.
The fuel system employs a multi-point sequential fuel
injection architecture with returnless fuel delivery in later variants. Fuel
pressure is regulated at approximately 3.0 bar (43.5 psi) and delivered to four
injectors per bank positioned in the intake ports. The intake manifold is
constructed from aluminum and features separate plenums for each cylinder bank.
The sequential injection timing is controlled by the Engine Control Unit (ECU)
based on crankshaft position, camshaft position, and engine load. The system
incorporates a fuel evaporative emissions control system that purges fuel vapors
from the charcoal canister into the intake manifold. In Phase-II variants, the
ECU utilizes mass airflow sensors on each intake tract for precise load
calculation.
The lubrication system is a forced-feed, wet-sump type
utilizing a rotor-type oil pump mounted to the front of the crankshaft. The pump
is driven directly by the crankshaft, ensuring immediate oil pressure upon
startup. Oil is drawn from a stamped steel oil pan through a baffled strainer
before pressurization. A full-flow spin-on oil filter is mounted externally on
the cylinder block.
The system supplies lubricant to the crankshaft main bearings, connecting rod
bearings, camshaft bearings, bucket tappets, timing belt tensioner, and both
turbocharger center bearings. An oil-to-water heat exchanger integrated into the
oil filter housing maintains oil temperature within optimal ranges. In
high-performance variants (EJ20R, EJ208), an additional air-to-oil cooler is
mounted at the front of the engine to manage thermal loads under sustained
high-speed operation.
The cooling system is a pressurized, water-cooled setup
utilizing a centrifugal water pump driven by the engine's timing belt. A
wax-type thermostat with a rated opening temperature of 76°C (169°F) for early
variants or 82°C (180°F) for Phase-II variants regulates the engine operating
temperature. Coolant circulates through the aluminum cylinder blocks and
cylinder heads before passing through a cross-flow radiator.
An additional coolant circuit serves both turbocharger bearing housings,
providing cooling after engine shutdown to prevent oil coking. The intercooler
system varies by variant: early models (EJ20H, EJ20R) utilize a water-to-air
intercooler with a dedicated coolant circuit and front-mounted heat exchanger;
Phase-II variants (EJ206, EJ208) utilize a top-mount air-to-air intercooler
positioned above the engine.
| Intake and Exhaust Systems |
Intake System: A dual-stage intake manifold with
variable length runners is utilized on Phase-II variants (EJ206, EJ208), with a
switching valve that alters runner length based on engine speed to optimize
torque characteristics.
Exhaust System: The exhaust system incorporates separate manifolds for each
cylinder bank, with the primary turbocharger receiving exhaust flow from the
right bank and the secondary turbocharger receiving flow from the left bank
through the exhaust switching valve. A catalytic converter is integrated into
each exhaust downpipe, with oxygen sensors for closed-loop fuel control.
The engine utilizes a direct ignition system with
individual pencil-type ignition coils mounted directly over each spark plug. The
coil-on-plug design eliminates high-tension spark plug wires. The ignition
system is fully integrated with the ECU, which controls spark timing based on
engine speed, load, coolant temperature, and knock sensor input.
Sequential Twin-Turbo System: The induction system
employs two turbochargers arranged in sequence. A primary turbocharger (small
frame) provides boost from low engine speeds, while a secondary turbocharger
(larger frame) is brought online through a series of exhaust and intake valves
controlled by the ECU. The system utilizes an exhaust switching valve that
directs exhaust flow to the secondary turbo when engine speed and load reach
predetermined thresholds. An intake switching valve controls the routing of
compressed air from the two turbochargers into the intercooler. The transition
between single and twin-turbo operation occurs between 3,500 and 4,500 rpm
depending on variant and engine load.
Turbocharger Specifications: Primary turbocharger is typically an IHI RHF4 or VF
series unit with a small turbine housing for rapid spool. Secondary turbocharger
is a larger IHI VF series unit. Both turbochargers feature water-cooled bearing
housings and integral wastegates controlled by the ECU via boost control
solenoids.
Overall Engine Length: 550 mm (21.65 in).
Overall Engine Width: 730 mm (28.74 in) measured across the cylinder heads.
Overall Engine Height: 640 mm (25.20 in).
Dry Weight: The complete engine assembly weighs 145 kg (320 lb) for early
variants and 150 kg (331 lb) for Phase-II variants, inclusive of turbochargers,
intercooler system, and ancillary components.
Engine Oil Capacity (with Filter): 4.5-5.0 liters
(4.8-5.3 qt), varying with oil cooler configuration. Engine Oil Specification:
SAE 10W-40, 5W-40, or 5W-30 meeting API SG or higher classification. Full
synthetic oil is recommended for turbocharged variants. Coolant Capacity:
7.0-8.0 liters (7.4-8.5 qt) inclusive of radiator, heater circuit, turbocharger
cooling, and water-to-air intercooler circuit on early variants.
Spark Plug Type: NGK PFR6B or equivalent platinum-tipped plug for Phase-I; NGK
ILFR6B or equivalent for Phase-II. Spark Plug Gap: 0.7-0.8 mm (0.028-0.031 in).
Spark Plug Replacement Interval: 60,000 km (37,000 mi). 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).
Adjustment requires shim replacement under the bucket tappets. Valve Clearance
Inspection Interval: 100,000 km (62,000 mi).
Timing Belt Replacement Interval: 100,000 km (62,000 mi) or 5 years, whichever
occurs first. Failure to replace the timing belt at the recommended interval
risks catastrophic engine damage due to the interference design. Timing Belt
Tensioner Inspection: The automatic tensioner should be replaced with each
timing belt service. Fuel Filter Replacement Interval: 40,000 km (25,000 mi).
Cylinder Head Bolts, Step 1: 29.0 Nm (3.0 kgf-m, 21
lb-ft).
Cylinder Head Bolts, Step 2: 69.0 Nm (7.0 kgf-m, 51 lb-ft).
Main Bearing Cap Bolts, Step 1: 20.0 Nm (2.0 kgf-m, 15 lb-ft).
Main Bearing Cap Bolts, Step 2: 39.0 Nm (4.0 kgf-m, 29 lb-ft).
Connecting Rod Cap Bolts, Step 1: 20.0 Nm (2.0 kgf-m, 15 lb-ft).
Connecting Rod Cap Bolts, Step 2: 45.0 Nm (4.6 kgf-m, 33 lb-ft).
Camshaft Bearing Cap Bolts: 20.0 Nm (2.0 kgf-m, 15 lb-ft).
Intake Manifold Bolts: 20.0-25.0 Nm (2.0-2.5 kgf-m, 15-18 lb-ft).
Exhaust Manifold Nuts: 35.0-40.0 Nm (3.6-4.1 kgf-m, 26-30 lb-ft).
Crankshaft Pulley Bolt: 177.0 Nm (18.0 kgf-m, 130 lb-ft).
Spark Plugs: 25.0-30.0 Nm (2.5-3.1 kgf-m, 18-22 lb-ft).
Oil Filter (Spin-on Type): 14.0 Nm (1.4 kgf-m, 10 lb-ft).
Turbocharger Mounting Nuts: 35.0-40.0 Nm (3.6-4.1 kgf-m, 26-30 lb-ft).
Flywheel / Drive Plate Bolts: 70.0 Nm (7.1 kgf-m, 52 lb-ft).
Timing Belt Tensioner Bolt: 39.0 Nm (4.0 kgf-m, 29 lb-ft).
The Subaru EJ20TT engine was utilized exclusively in
right-hand drive models due to the complex plumbing of the sequential twin-turbo
system occupying space incompatible with left-hand drive steering components.
Subaru Legacy / Liberty (BD5/BG5 Generation,
1993-1998)
Legacy RS: EJ20H and EJ20R variants in manual and automatic configurations.
Legacy GT: EJ20H and EJ20R variants across sedan and wagon body styles.
Legacy GT-B: High-performance wagon variant utilizing EJ20R with 280 PS output.
Subaru Legacy B4 / GT-B (BE5/BH5 Generation,
1998-2003)
Legacy B4: Sedan variant with EJ206 (automatic) and EJ208 (manual) engines.
Legacy GT-B: Wagon variant with EJ206 (automatic) and EJ208 (manual) engines.
Legacy RSK (Revolver Sports Kompressor): Performance-oriented B4 variant with
EJ208 engine.
Subaru Liberty B4 (Australian Market): Select years in the Australian market
received the EJ206 and EJ208 engines in the Liberty B4 performance sedan,
representing one of the few left-hand drive applications of the EJ20TT outside
Japan.
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