Subaru FB engine

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title: "Subaru FB engine" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["subaru-engines", "boxer-engines", "gasoline-engines-by-model", "four-cylinder-engines"] topic_path: "sports" source: "https://en.wikipedia.org/wiki/Subaru_FB_engine" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::data[format=table title="Infobox automobile engine"]

FieldValue
image5th gen Subaru Impreza FB20 engine in Automobile Council 2016.jpg
nameSubaru FB engine
manufacturerSubaru
configurationFlat-4
production2010–present
predecessorEJ
successorFA, CB
displacement{{ubl
{{cvt1599
{{cvt1995
{{cvt2498
bore{{ubl
stroke{{ubl
power84 –
torque15.3 –
valvetrainDOHC 4 valves x cyl. with AVCS
turbochargerOptional
coolingsystemWater-cooled
fuelsystemFuel injection
fueltypeGasoline
compression10.5:1, 11.0:1, 12.5:1
::

| image = 5th gen Subaru Impreza FB20 engine in Automobile Council 2016.jpg | name = Subaru FB engine | manufacturer = Subaru | configuration = Flat-4 | production = 2010–present | predecessor = EJ | successor = FA, CB | displacement = {{ubl | 1599 cc | 1995 cc | 2498 cc | bore = {{ubl | 78.8 mm (FB16) | 84 mm (FB20) | 94 mm (FB25) | stroke = {{ubl | 82 mm (FB16) | 90 mm (FB20 & FB25) | power = 84 – | torque = 15.3 – | valvetrain = DOHC 4 valves x cyl. with AVCS | turbocharger = Optional | coolingsystem = Water-cooled | fuelsystem = Fuel injection | fueltype = Gasoline | compression = 10.5:1, 11.0:1, 12.5:1

The Subaru FB engine is the third generation of gasoline boxer-4 engine used in Subaru automobiles, and was announced on 23 September 2010. It follows the previous generation EJ-series engine which was introduced in 1989 and the first generation EA-series which was introduced in 1966. By increasing piston stroke and decreasing piston bore, Subaru aimed to reduce emissions and improve fuel economy, while increasing and broadening torque output compared to the EJ-series.

The Subaru FA engine series was derived later from the FB, but the two engine families share only a few common parts. In 2020, Subaru introduced the CB18 engine with improved efficiency to succeed the FB in several applications.

Overview

Unofficially, Subaru stated that "FB" stands for "FHI/Future and Brand New/Boxer". The FB has an all new block and head featuring dual overhead cams with intake and exhaust variable valve timing (which Subaru designates as AVCS, standing for Active Valve Control System), and a timing chain that replaced the timing belt. Moving to chain-driven cams is said to allow the valves to be placed at a narrower angle to each other and shrink the bore of cylinders from 99.5 to. It results in less unburned fuel during cold start, thereby reducing emissions. Subaru was able to maintain the exterior dimensions substantially unchanged by making the cylinder heads smaller. The FB is only marginally heavier than an equivalent-displacement EJ. In Jan 2011, Car and Driver was told direct injection would be added soon, which became reality by the introduction of FB16DIT in 2014.

Subaru claims a 28-percent reduction in friction losses, mainly due to the addition of roller rockers in between the cam and the valve, A lighter 0W-20 oil in combination with a compact oil pump is also credited with contributing to the reduction in friction losses. The FB has a 10% improvement in fuel economy

The compression ratio is slightly higher, and the stroke has increased compared to the EJ engine; previously, the chassis precluded a longer stroke. These changes improve combustion efficiency and allow higher torque at lower speeds. The FB is built at Gunma Oizumi Plant and was initially available as a 2.5 litre displacement engine, starting in Forester models, with 1.6 and 2.0 litre versions to follow in Imprezas.

FB16

All FB16 variants:

  • Displacement: 1600 cc DOHC
  • Bore x stroke: 78.8x82 mm

FB16

::figure[src="https://upload.wikimedia.org/wikipedia/commons/b/be/Subaru_FB16_NA.JPG" caption="Subaru FB16"] ::

FB16 DIT

::figure[src="https://upload.wikimedia.org/wikipedia/commons/4/40/Subaru_1.6_DIT_engine.jpg" caption="Subaru FB16 DIT"] ::

The FB16 direct injection turbocharged (DIT) engine is the first FB-series engine with a turbocharger, and includes direct injection with an auto stop/start system. It is the base engine in the first-generation (2014–20 model years) Subaru Levorg. The Levorg also has an option for a 2.0 litre direct injection turbo engine, the FA20F. The design target for the FB16 DIT engine was to equal or exceed the performance of the FB25 naturally-aspirated engine fitted to the Legacy, using regular gasoline, according to the designer, Rei Sasaki. Although it shares its displacement with the naturally aspirated FB16, the only part the two engines share is the crankshaft. As fitted to the Levorg (1,540kg, CVT), the FB16 DIT was able to achieve fuel economy of 16.0 km/L on the JC08 cycle, compared to 15.6 km/L of FB16 on Impreza G4 (1,320kg, CVT).

  • Compression: 11.0:1
  • Application: 2014–20 Subaru Levorg
    • Power: 125 kW at 4,800–5,600 RPM
    • Torque: 25.5 kgm at 1,800–4,800 RPM

FB20

The prior EJ20 used an oversquare 92 × bore and stroke for a 1994 cc swept displacement; in comparison, the FB20 features an undersquare bore and stroke for a slightly larger displacement.

All FB20 variants:

  • Displacement: 1995 cc DOHC
  • Bore x stroke: 84 ×

FB20B

::figure[src="https://upload.wikimedia.org/wikipedia/commons/7/71/2015_Subaru_XV_2.0i_FB20_engine.jpg" caption="Subaru FB20B"] ::

FB20X

::figure[src="https://upload.wikimedia.org/wikipedia/commons/f/f2/The_engine_room_of_Subaru_IMPREZA_SPORT_HYBRID_2.0i-S_EyeSight_(DAA-GPE).JPG" caption="Subaru FB20X"] ::

The existing FB20B was modified by reducing internal friction for the hybrid drivetrain, which incorporates an electric motor in the Lineartronic CVT. The high-voltage traction battery is installed below the cargo area for better weight balance. Combined system power is stated to be 160 hp. Output of the gasoline engine is comparable to that of the non-hybrid FB20B.

  • Compression: 10.8:1
  • Application: 2014–16 Subaru XV/Crosstrek Hybrid
  • Combined system output:
    • Power: 160 hp at 6,000 rpm
    • Torque: 163 lbft at 2,000 rpm
  • Gasoline engine output:
    • Power: 148 hp
    • Torque: 145 lbft
  • Electric motor output:
    • Power: 13.4 hp
    • Torque: 48.0 lbft

FB20D

Used in the fifth generation Impreza sedan and hatchback; compared to the FB20B, the FB20D adds direct injection, providing a slight increase in power and efficiency.

  • Compression: 12.5:1
  • 2017+ Subaru Impreza and 2018–2025 Subaru XV/Crosstrek
    • Power (JDM, USDM) : 113 kW at 6,000 RPM
    • Power (EUDM, AUDM, THDM): 115 kW at 6,000 RPM
    • Torque: 20 kgm at 4,000 RPM ::figure[src="https://upload.wikimedia.org/wikipedia/commons/e/ec/SUBARU_FB20D_ENGINE.jpg" caption="Subaru FB20D Engine"] ::

FB20V

The 2019 Crosstrek is available with a plug-in hybrid system sourced from Toyota. The new hybrid drivetrain uses two motor-generator units; the traction motor (MG2) and battery are significantly larger compared to the previous XV Crosstrek Hybrid, and the vehicle is capable of moving under electric power alone for a limited distance. MG2 is used under parallel hybrid operation as well. MG1 is used as the starter motor and charges the battery for series hybrid operation. The direct-injection FB20V in the revised hybrid is detuned compared to the conventional FB20D.

  • Application: 2019+ Subaru Crosstrek Hybrid (PHEV)
  • Combined system output:
    • Power: 148 hp
  • Gasoline engine output:
    • Power: 137 hp at 5,600 RPM
    • Torque: 134 lbft at 4,400 RPM
  • Electric traction motor (MG2) output:
    • Power: 118 hp
    • Torque: 149 lbft

FB20D e-Boxer

The direct-injection FB20D was also used in a mild parallel hybrid configuration similar to the FB20X. The mild hybrid drivetrain was fitted to selected trims for models sold in Japan (Forester, July 2018 and XV, October 2018), Europe (same models, starting in 2019), and Australia (same models, starting in 2020).

  • Application: 2019+ JDM and EUDM Subaru XV and Forester, selected models
  • Combined system output:
    • Power: 107 kW at 6,000 rpm
    • Torque: 188 Nm at 4,000 rpm
  • Gasoline engine output:
    • Power: 145 PS
    • Torque: 188 Nm
  • Electric motor output:
    • Power: 10 kW
    • Torque: 65 Nm

FB25

Compared to the previous EJ25, which had a displacement of 2457 cc from an oversquare 99.5 × bore and stroke, the FB25 has slightly larger displacement on a less oversquare bore and stroke.

All FB25 variants:

  • Displacement: 2498 cc DOHC
  • Bore x stroke: 94 ×

FB25B

::figure[src="https://upload.wikimedia.org/wikipedia/commons/b/bd/Ray_Baldwin_Subaru_Stamford_NY_Auto_Show_021.JPG" caption="Subaru FB25B"] ::

  • Compression: 10.0:1
  • Power: 170 hp at 5,800 rpm
  • Torque: 174 lbft at 4,100 rpm
  • Application:

FB25D

::figure[src="https://upload.wikimedia.org/wikipedia/commons/6/65/2023_Subaru_Outback_Limited_2.5_liter_4_cyl_engine_bay.jpg" caption="Subaru FB25D"] ::

The 2019 model year Subaru Forester was introduced at the 2018 New York International Auto Show with a revised version of the FB25 engine featuring direct injection, resulting in a slight boost in power and fuel economy. The seventh-generation 2020 model year Legacy and Outback also adopted the revised direct-injection FB25D as its base engine. For Strong Hybrid applications, the engine makes 162 horsepower, with an additional electric motor rated at 118 hp and 199 pound-feet, can produce as much as 194 horsepower if combined.

  • Compression: 12.0:1
  • 2019–2025 Subaru Forester, 2020–2025 Subaru Legacy (non-XT, non-Sport), 2020–2025 Subaru Outback (non-XT, non-Wilderness), 2021–2023 Subaru Crosstrek (U.S. Sport and Limited trims; Canadian Outdoor and Limited trims)
    • Power: 182 hp at 5,800 rpm
    • Torque: 176 lbft at 4,400 rpm
  • 2024–2025 Subaru Crosstrek (U.S. Premium, Sport, Limited, and Wilderness trims; Canadian Onyx, Limited, and Wilderness trims), 2024–2025 Subaru Impreza (RS trim)
    • Power: 182 hp at 5,800 rpm
    • Torque: 178 lbft at 3,700 rpm
  • 2025+ Subaru Forester, 2026+ Subaru Outback (non-XT, non-Wilderness), 2026+ Subaru Crosstrek (all trims), 2026+ Subaru Impreza (RS trim)
    • Power: 180 hp at 5,800 rpm
    • Torque: 178 lbft at 3,700 rpm
  • 2025+ Subaru Forester Hybrid, 2026+ Subaru Crosstrek Hybrid
    • Power: 162 hp (engine only) & 194 hp (combined)
    • Torque: 154 lbft at 3,700 rpm

Notes

References

References

  1. (23 September 2010). "FHI Develops a New-generation Subaru Boxer Engine". [[Fuji Heavy Industries]].
  2. Tanigawa, Kiyoshi. (29 September 2010). "スバル、新世代水平対向エンジン「FB型」説明会". Car Watch.
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  5. dgvffd. (19 Nov 2007). "Pulling pistons out of Subaru block".
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  7. Bremner, Richard. (17 January 2011). "Subaru Forester 2.0 XS review". [[Haymarket Media Group]].
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