Subaru FB20 Specifications
| Engine Model: Subaru FB20 |
| Engine Type: 4-cycle 4-cylinder DOHC 16-valve liquid-cooled gasoline |
| Total Displacement: 121.7 cu.in (1.99 L) |
| Rated Engine Power: 148-154 Hp (110-115 kW) at 6000 rpm |
| Fuel System Type: Multi-point fuel injection or direct injection |
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The Subaru FB20 is a 2.0-liter, naturally aspirated
horizontally opposed Boxer engine introduced in 2010 as the foundational
powerplant for Subaru’s fourth-generation Impreza. Representing the first
clean-sheet redesign of Subaru’s Boxer engine architecture since the
introduction of the EJ series in 1989, the FB20 was engineered to address the
competing demands of reduced fuel consumption, lower emissions, and enhanced
low-end torque delivery. The development focused on friction reduction, thermal
efficiency, and improved packaging within Subaru’s global vehicle platforms.
The FB20 family encompasses three distinct iterations: the original FB20B with
multi-port fuel injection, the FB20D with high-pressure direct injection, and
the FB20X with hybrid system integration capability. Across all variants, the
engine adopted a long-stroke architecture with bore and stroke dimensions of
84.0 mm and 90.0 mm respectively, a reversal of the oversquare configuration
used in EJ-series engines.
This change prioritized low-end torque and thermal efficiency over high-rpm
power. The valvetrain transitioned from belt-driven to chain-driven camshafts,
eliminating the scheduled timing belt replacement service. Dual Active Valve
Control System (AVCS) on both intake and exhaust camshafts provided continuously
variable valve timing across the operating range.
The cooling system incorporated separate circuits for the cylinder block and
cylinder heads, enabling independent temperature management to reduce internal
friction while mitigating knock tendency. The FB20 became the standard engine
for Subaru’s compact global platforms, including the Impreza, XV/Crosstrek, and
Forester in markets where the 2.0-liter displacement served as the primary
powertrain.
Engine Type: Horizontally opposed (Boxer) 4-cylinder, 4-cycle, naturally
aspirated.
Displacement: 1,995 cc (121.7 cu.in).
Bore: 84.0 mm (3.31 in).
Stroke: 90.0 mm (3.54 in).
Compression Ratio: 10.5:1 for FB20B; 12.5:1 for FB20D and FB20X.
Firing Order: 1-3-2-4.
Maximum Power (FB20B): 110-112 kW (148-150 hp) @ 6,200 rpm.
Maximum Power (FB20D / FB20X): 113-115 kW (152-154 hp) @ 6,000 rpm.
Maximum Torque (FB20B): 196-198 Nm (145-146 lb-ft) @ 4,200 rpm.
Maximum Torque (FB20D / FB20X): 196-198 Nm (145-146 lb-ft) @ 4,000 rpm.
Redline: 6,500-6,800 rpm depending on variant and ECU calibration.
Valvetrain Configuration: Dual Overhead Camshaft (DOHC) per cylinder bank,
operating 16 valves (4 valves per cylinder). Dual Active Valve Control System
(AVCS) on intake and exhaust camshafts. Camshafts are driven by a silent-type
timing chain.
The cylinder block is manufactured from cast aluminum
alloy using high-pressure die-casting techniques. The block incorporates the
traditional Subaru Boxer configuration with a 180-degree cylinder bank angle,
yielding a low center of gravity and a compact overall length suitable for
longitudinal mounting in all-wheel drive platforms. The block is designed with
an open-deck configuration, where the cylinder bores are supported at the upper
and lower extremes with coolant passages surrounding the upper bore regions to
optimize cooling efficiency.
The cylinder bores are cast-in-place iron liners, centrifugally cast and
machined to final specification. Bore diameter measures 84.0 mm (3.31 in) with a
piston stroke of 90.0 mm (3.54 in), yielding a total displacement of 1,995 cc
(121.7 cu.in). This under-square bore-to-stroke ratio (0.933) represents a
significant departure from the oversquare EJ-series engines, prioritizing
low-end torque generation and thermal efficiency over high-rpm power. The
increased stroke length was accommodated through the use of asymmetrical
connecting rods - split at an angle (offset) - which allowed the longer stroke
without increasing the overall width of the engine block, preventing
interference with vehicle frame rails.
The crankshaft is manufactured from forged micro-alloy steel with
induction-hardened journal surfaces. Five main bearings support the crankshaft,
with main bearing journal diameter measuring 58.0 mm (2.28 in). Thrust washers
positioned at the center main bearing control axial crankshaft play. Connecting
rods are forged from high-carbon steel with a fracture-split big end design.
Pistons are cast aluminum with a low-friction skirt coating and a reduced
compression height to accommodate the longer stroke. The piston ring pack
incorporates low-tension rings to reduce friction, with a compression ring, a
tapered second ring, and a three-piece oil control ring.
Early production engines (2012-2014)
experienced elevated oil consumption due to the low-tension ring design;
subsequent revisions incorporated modified ring geometry to improve oil
control. Oil squirters (piston cooling jets) are integrated into the
cylinder block, directing pressurized oil to the underside of each
piston crown to manage thermal loads.
Two cylinder heads are utilized, one for each cylinder
bank, manufactured from aluminum alloy. The cross-flow design separates intake
and exhaust passages to opposite sides of each head. The combustion chambers are
of the pent-roof configuration with four valves per cylinder and a centrally
located spark plug.
Each cylinder head contains 16 valves: eight intake valves and eight exhaust
valves across both banks. Intake valve diameter measures 32.0 mm (1.26 in),
while exhaust valve diameter measures 28.0 mm (1.10 in). Valve stem diameter is
5.5 mm (0.22 in) for both intake and exhaust. The valvetrain utilizes roller
rocker arms to reduce friction at the cam-to-valve interface.
The Dual Active Valve Control System (AVCS) is applied to both intake and
exhaust camshafts on each cylinder bank. Hydraulic camshaft phasers, actuated by
oil control valves (OCVs) commanded by the engine control unit, provide
continuously variable valve timing.
Intake camshaft phasing range is 50 degrees
crankshaft angle; exhaust camshaft phasing range is 40 degrees. The
system enables precise control of valve overlap to optimize volumetric
efficiency, enable internal exhaust gas recirculation for emissions
reduction, and reduce pumping losses under light load conditions.
The camshafts are driven by a silent-type timing chain with a pitch of
8.0 mm (0.31 in). The chain routes from the crankshaft sprocket to the
left bank exhaust camshaft sprocket, then to the right bank exhaust
camshaft sprocket. Separate chain segments connect the exhaust camshaft
to the intake camshaft on each bank. An automatic hydraulic tensioner,
supplied with engine oil pressure, maintains consistent chain tension
throughout the engine’s service life.
The timing chain is designed for the life of the engine under normal
operating conditions, eliminating the scheduled replacement interval
required for belt-driven EJ-series engines. Valve clearance is
maintained via hydraulic lash adjusters integrated into the cylinder
head casting, operating in conjunction with the roller rocker arms. No
periodic valve adjustment is required.
The FB20 was produced with two distinct fuel system
configurations. The FB20B employs a multi-point electronic fuel injection system
(MPFI) operating in sequential mode. Fuel injectors are top-feed,
solenoid-actuated units with six-hole nozzles, mounted in the intake manifold
runners. System fuel pressure is regulated at 3.0-3.5 bar (44-51 psi). The
intake manifold is constructed from aluminum alloy on early FB20B variants,
transitioning to composite plastic on later production to reduce weight and
minimize heat soak.
The FB20D and FB20X employ a high-pressure direct injection system operating at
pressures up to 200 bar (2,900 psi). A two-stage fuel delivery system comprises
a low-pressure pump within the fuel tank supplying fuel at 4.0-6.0 bar (58-87
psi) to a high-pressure pump mounted on the cylinder head. The high-pressure
pump is a single-piston, quantity-controlled unit driven by a cam lobe on the
left bank exhaust camshaft. Fuel rail pressure is modulated by the engine
control unit based on load and engine speed.
The injectors are solenoid-actuated units with six-hole nozzles, mounted
centrally in the cylinder heads to direct fuel directly into the combustion
chamber. Multiple injection events per combustion cycle - including pilot
injection, main injection, and post-injection - are utilized to reduce
combustion noise and enable particulate filter regeneration where equipped. The
direct injection system enables the higher compression ratio of 12.5:1 by
providing charge cooling within the combustion chamber, reducing knock tendency.
The throttle body is an electronically controlled unit (drive-by-wire) with a
bore diameter of 65 mm (2.56 in) across all variants.
The lubrication system utilizes a forced-feed,
full-flow design with a trochoid-type oil pump mounted to the front of the
crankshaft. The pump is driven directly by the crankshaft nose, providing oil
flow proportional to engine speed. A pressure relief valve integrated into the
pump maintains system pressure within design parameters.
Total oil capacity including filter is 4.8-5.2 liters (5.1-5.5 qt). Recommended
oil viscosity is 0W-20 full synthetic meeting API SN or ILSAC GF-5
specifications. The use of 0W-20 viscosity is critical for the proper function
of the hydraulic timing chain tensioner and AVCS phasers, which rely on precise
oil pressure and flow characteristics. Oil pressure specifications require a
minimum of 0.8 bar (12 psi) at warm idle and 3.0-4.0 bar (44-58 psi) at 3,000
rpm.
The oil filter is a spin-on, full-flow type mounted to the cylinder block. A
liquid-to-oil plate-type oil cooler is integrated into the lubrication system,
mounted between the oil filter and the cylinder block, utilizing engine coolant
to stabilize oil temperature. The oil pan is stamped steel with internal
baffling.
The cooling system is pressurized and utilizes a
centrifugal water pump driven by the accessory drive belt. The pump features a
cast aluminum housing and a composite impeller. A distinctive feature of the
FB20 cooling system is the separation of cooling circuits for the cylinder block
and cylinder heads. This configuration allows the cylinder block to operate at a
higher temperature (reducing internal friction) while maintaining lower
temperatures in the cylinder heads to prevent knock, particularly on the
high-compression direct injection variants.
Thermostat type is a wax-pellet unit with electronic control. Opening
temperature is 82-86 °C (180-187 °F), with the ECU capable of modulating the
thermostat to achieve optimal thermal management.
Total coolant capacity ranges from 7.0-8.0 liters (7.4-8.5 qt), inclusive of the
engine block, radiator, heater core, and oil cooler circuit. The radiator is a
cross-flow aluminum core with plastic end tanks. Cooling fan configuration
consists of dual electric fans controlled by the engine control unit. System
pressure is controlled by a radiator cap rated at 1.1 bar (16 psi).
| Intake and Exhaust Systems |
Ignition System: The ignition system utilizes
direct-acting ignition coils mounted over each spark plug (coil-on-plug). Spark
plug type is iridium-tipped with a gap of 1.0-1.1 mm (0.039-0.043 in). Spark
plug replacement interval is 100,000 km (62,000 mi). Spark plug torque is 20-25
Nm (15-18 lb-ft).
Exhaust System: The exhaust manifold is manufactured from tubular stainless
steel with a 4-2-1 configuration to optimize exhaust pulse scavenging. The
system incorporates a three-way catalytic converter with closed-loop oxygen
sensor feedback. Two oxygen sensors are utilized: a front air-fuel ratio sensor
upstream of the catalytic converter and a rear oxygen sensor downstream for
catalyst monitoring. Direct injection variants (FB20D/FB20X) are equipped with
an Otto particulate filter in certain markets to meet particulate emission
standards.
Aspiration System: The FB20 is naturally aspirated.
Intake air passes through a panel-type dry paper filter element housed in a
resonance chamber, then through the electronically controlled throttle body and
intake manifold. The intake manifold on FB20D and FB20X variants incorporates
integrated intake air tumble control valves to enhance air-fuel mixing under
low-load conditions.
Engine Management: The ECU varies by variant. FB20B utilizes a 16-bit or 32-bit
ECU managing fuel injection, ignition timing, dual AVCS operation, idle speed
control, and cooling fan operation. FB20D and FB20X utilize a 32-bit ECU with
additional controls for direct injection high-pressure fuel system, tumble
control valves, and, on FB20X, hybrid system integration including motor assist
and regenerative braking coordination.
Crankcase Ventilation: A closed-loop PCV system routes blow-by gases from the
cylinder block and valve covers through an integrated oil separator. A PCV valve
is mounted on the intake manifold. A clogged PCV valve is a known cause of
elevated oil consumption and requires periodic inspection.
Overall Length: 620 mm (24.4 in) measured from
accessory drive pulley face to transmission mounting flange.
Overall Width: 860 mm (33.9 in) inclusive of the cylinder heads and intake
manifold assembly.
Overall Height: 620 mm (24.4 in) from oil pan bottom surface to intake manifold
top surface.
Dry Weight: 130-135 kg (287-298 lb) depending on fuel system configuration and
accessory equipment.
Valve Clearance: Hydraulic lash adjusters operate
automatically. No periodic adjustment required. Timing Chain: Designed for
engine life under normal operating conditions. Inspection recommended if unusual
noise from timing case is observed. Spark Plug Replacement Interval: 100,000 km
(62,000 mi) for iridium-tipped plugs. Spark plug torque: 20-25 Nm (15-18 lb-ft).
Coolant Change Interval: 100,000 km (62,000 mi) or 5 years.
Engine Oil Change Interval: 8,000 km (5,000 mi) for standard driving conditions;
5,000 km (3,100 mi) for severe service including frequent short trips, towing,
or dusty environments. Full synthetic 0W-20 oil required. Oil Filter Replacement
Interval: Replace with every oil change. PCV Valve Inspection Interval: 40,000
km (25,000 mi). Replacement recommended if valve shows signs of clogging or
sticking.
Fuel Filter Replacement Interval: The in-tank filter is part of the fuel pump
module and is not a scheduled maintenance item. Replacement indicated only upon
pump failure or contamination. Air Filter Element Replacement Interval: 30,000
km (18,600 mi) or as indicated by inspection. Drive Belt (accessory) Replacement
Interval: 100,000 km (62,000 mi) or when cracking, glazing, or wear is observed.
Idle Speed (warm, neutral): 650-750 rpm, controlled by ECU.
Ignition Timing: Electronically controlled. No manual adjustment possible. Fuel
Pressure (FB20B MPFI): 3.0-3.5 bar (44-51 psi) measured at fuel rail with engine
running. Fuel Pressure (FB20D/FB20X DI): Low-pressure circuit: 4.0-6.0 bar
(58-87 psi). High-pressure circuit: 40-200 bar (580-2,900 psi) regulated by ECU.
Compression Pressure: Minimum 12.0 bar (174 psi) with no cylinder varying more
than 1.5 bar (22 psi) from others. Measured with engine warm, throttle fully
open.
Cylinder Head Bolts (cold), Step 1: 25 Nm (18 lb-ft).
Cylinder Head Bolts (cold), Step 2: 60 Nm (44 lb-ft).
Crankshaft Damper Pulley Bolt: 170-180 Nm (125-133 lb-ft).
Connecting Rod Cap Bolts: 35-40 Nm (26-30 lb-ft).
Main Bearing Cap Bolts, Step 1: 30 Nm (22 lb-ft).
Main Bearing Cap Bolts, Step 2: 60 Nm (44 lb-ft).
Flywheel / Drive Plate Bolts: 70-80 Nm (52-59 lb-ft).
Camshaft Sprocket Bolts (camshaft phasers): 50-60 Nm (37-44 lb-ft).
Camshaft Bearing Cap Bolts: 15-20 Nm (11-15 lb-ft).
Valve Cover Bolts: 8-10 Nm (6-7 lb-ft).
Intake Manifold Bolts: 18-22 Nm (13-16 lb-ft).
Exhaust Manifold Nuts: 25-30 Nm (18-22 lb-ft).
Oil Pan Bolts: 8-12 Nm (6-9 lb-ft).
Timing Chain Tensioner: 20-25 Nm (15-18 lb-ft).
Timing Chain Guide Bolts: 10-12 Nm (7-9 lb-ft).
Water Pump Mounting Bolts: 15-20 Nm (11-15 lb-ft).
Thermostat Housing Bolts: 8-12 Nm (6-9 lb-ft).
Fuel Rail Mounting Bolts (MPFI): 18-22 Nm (13-16 lb-ft).
High-Pressure Fuel Pump Mounting Bolts (DI): 20-25 Nm (15-18 lb-ft).
Spark Plugs: 20-25 Nm (15-18 lb-ft).
Crankshaft Position Sensor Mounting Bolt: 8-10 Nm (6-7 lb-ft).
Camshaft Position Sensor Mounting Bolts: 8-10 Nm (6-7 lb-ft).
Oxygen Sensors: 40-45 Nm (30-33 lb-ft).
Subaru Impreza (GJ / GP): 2012-2016 model years
(FB20B). The FB20 replaced the EJ-series engines in the fourth-generation
Impreza, providing improved fuel economy and a broader torque curve. The engine
was paired with a five-speed manual transmission or a continuously variable
transmission (CVT) in front-wheel drive and all-wheel drive configurations.
Subaru Impreza (GT / GK): 2017-present (FB20D). The fifth-generation Impreza
received the direct injection FB20D, delivering increased power and thermal
efficiency. The engine is paired with a five-speed manual transmission on base
models and a CVT on higher trims.
Subaru XV / Crosstrek (GP): 2012-2017 (FB20B). The first-generation XV/Crosstrek
received the FB20B with multi-port injection, calibrated for the increased ride
height and all-wheel drive standard configuration. A CVT is the primary
transmission pairing.
Subaru XV / Crosstrek (GT): 2018-present (FB20D). The second-generation
Crosstrek received the FB20D direct injection engine, providing improved low-end
torque suitable for the crossover application. A six-speed manual transmission
is available on base trims; CVT is standard on higher trims and hybrid
configurations.
Subaru Forester (SJ): 2012-2018 in non-US markets (FB20B). The fourth-generation
Forester received the FB20 as the base engine in markets where the 2.0-liter
displacement served as the primary powertrain, with the FB25 offered in North
American markets. The engine is paired with a six-speed manual transmission or
CVT.
Subaru Forester (SK): 2019-present in non-US markets (FB20D). The
fifth-generation Forester received the direct injection FB20D in markets where
the 2.0-liter engine is offered, providing improved fuel efficiency and
emissions compliance. The engine is paired exclusively with a CVT in most
configurations.
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