Subaru uses a four or five character code to identify all of their engines. As of August 2022 these are the engines presently in models sold by Subaru

Two-cylinder

Subaru EK engine

The EK series was an inline twin cylinder engine. Early versions were air-cooled two-stroke cycle, later replaced with water-cooled configurations in 1971. The engine was upgraded to a four-stroke SOHC in 1973 to meet Japanese Government emission regulations, using the SEEC emissions system (later SEEC-T), with an alloy block and head. The **** was used**** from**** 1958**** until 1989**** in**** most**** Kei car models****.****

Three-cylinder

The EF series engine is a liquid-cooled three-cylinder, four-stroke, with SOHC. It is not compliant with Japanese Government regulations concerning displacement of kei cars with a current maximum limit of 660 cc. The EF appeared while the EK was being replaced by the EN05.

Subaru EF engine

SOHC 2V, 55 hp at 5,200 rpm 1984–1987 Subaru Justy SOHC 3V, 66-73 hp 1987–1994 Subaru Justy

Four-cylinder

All of Subaru's four-cylinder engines (except the EN series) are liquid-cooled, horizontally opposed boxer four-strokes.

Subaru EA engine

The EA was used from 1966 until 1994 in most models. It is a basic two-valve-per-cylinder design with siamese ports, or one port that is directly next to another, and three main crankshaft main bearings. Engines with overhead camshafts were installed with two timing belts, whereas vehicles with overhead valves used timing gears exclusively.

Subaru EE engine (diesel)

Subaru unveiled the world's first boxer diesel engine to be fitted in a passenger car at the Geneva Auto Show in 2007. This 2.0L DOHC engine, designated the EE20, has an output of 110 kW at 3600 rpm and develops 350 Nm of torque at 1800 rpm, with a redline of 4750 rpm. The engine has a total displacement of 1998 cc from a square 86 × bore x stroke with a compression ratio of 16.3:1 and uses five main bearings. The EE20 shares a bore pitch dimension and assembly line with the EZ30 at the Ooizumi Factory; compared to the contemporaneous gasoline EJ20, which has a similar displacement, the EE20 is 61.3 mm shorter. The common rail solenoid injector is manufactured by Denso and operates at 180 MPa. The IHI variable geometry turbo is mounted under the right side of the engine, close to the exhaust manifold, reducing turbo lag. For the Legacy 2.0D, Subaru claimed consumption improved by 15 to 20% (ranging from 6.4 to 5.6 L/100km) and that emissions fell from 202 to 148 g/km compared to the similar model with a gasoline engine. Fuji Heavy Industries (FHI) spent three years starting in fall 2005 developing the EE20 after concluding the marque needed a diesel engine to compete in Europe. Details about the engine were first released in February 2008, after an additional preview at Frankfurt in 2007, and an official announcement of applications was made at Geneva in March 2008. The EE20 was originally released with Euro-4 emissions compliance; an oxidation catalyst and diesel particulate filter are mounted close to the turbo, using heat from exhaust gases, and the exhaust gas recirculation system is water-cooled to meet regulations. The compliance was soon updated to Euro-5 and Euro-6 in 2015. Per the March 2008 announcement at Geneva, the EE20 was sold in Legacy (wagon and sedan) and Outback vehicles for the European market; the diesel was only offered with a manual transmission at first, and the clutch and flywheel were specifically modified for diesel use. In September 2008, FHI announced the EE20 would be available as a slightly modified variant (the diesel particulate filter was now closed) in Forester and Impreza models sold in Europe starting that fall. For the Forester, output was reduced slightly to 108 kW. The EE20 was offered with the Impreza XV at that model's launch in 2010. The Subaru continuously variable transmission (branded Lineartronic) was offered as an option for EE20-equipped Outback models starting in 2013, and sales of the Lineartronic EE20 Outback would start in Australia later in 2013. At Geneva 2013, the diesel boxer was combined with three electric motors to form the hybrid powertrain of the Subaru VIZIV Concept. The Lineartronic EE20 powertrain was added to the Forester in 2015. In 2016, citing increasingly stringent emissions standards, the project manager for the Impreza stated that further development of the EE20 had been halted. In September 2017, Subaru announced production of diesel automobiles would end by 2020; at the time, sales were approximately 15,000 diesel-powered cars annually in Europe and Australia. The capacity gained would be used to start producing plug-in hybrids in 2018 and electric vehicles by 2021. At Geneva in March 2018, Subaru UK confirmed its parent company's plans to discontinue diesel production, but had enough stock on hand to meet projected demand through the end of 2018.

Subaru EJ engine

The EJ engine was introduced in the 1989 Subaru Legacy to replace the EA engines. It was designed from scratch with five main crankshaft bearings and four valves per cylinder and can be either SOHC or DOHC and one timing belt. The fifth digit is the only way to tell without seeing the engine. Generally the EJ-series can be divided into two versions: the Phase I engines (1989–1998) and the Phase II engines (1999–2010). The Phase II engines featured new cylinder heads and crankshafts with the thrust bearing located at crank bearing #5 instead of #3. The designation also changed from Phase I to Phase II. All Phase I engines have an alphanumerical suffix behind the standard EJXX designation, all Phase II engines have a numerical suffix behind the EJXX designation. Example: Phase I: EJ15E, EJ15J, EJ16E, EJ18E, EJ20B, EJ20D, EJ20E, EJ20G, EJ20H, EJ20J, EJ20R, EJ20K, EJ22E, EJ221, EJ25D Phase II: EJ151, EJ161, EJ181, EJ201, EJ202, EJ203, EJ204, EJ205, EJ206, EJ207, EJ208, EJ222, EJ251, EJ252, EJ253, EJ254, EJ255, EJ257, EJ20X, EJ20Y

Subaru EL engine/Boxer type 3

The **** replaced**** the EJ15**** and is**** used**** in**** the JDM Subaru**** Impreza 1.5R**** (series GD****,**** GG****,**** GE****,**** GH****)**** starting**** with**** model year**** 2006****.**** It is based on the EJ engine and shares many components, like the crankshaft from the EJ25. It has DOHC cylinder heads with AVCS variable valve timing on the intake.

Subaru EN engine

The Subaru EN inline-four engine was introduced in 1988 to replace the straight-two EK series engine that was originally engineered as an air-cooled engine, then modified as a water-cooled engine used in the 1969–1972 Subaru R-2. The EN was used in all kei cars and kei trucks in production by Subaru up until 2012.

Subaru FA engine

**** The FA**** was developed from**** the FB**** engine****,**** however,**** efforts to**** reduce**** weight**** while maintaining durability**** were**** the main**** goals of**** the FA**** engine****.**** While the FA and FB engines share a common platform, the FA shares very little in dedicated parts with the FB engine, with a different block, head, connecting rods, and pistons.

Subaru FB engine

The FB-series (initially available as naturally-aspirated engines in 2.5 and 2.0 litre displacements) is the first new generation of boxer engine since the EJ-series. Subaru announced details of the FB engine on 23 September 2010. By increasing piston stroke and decreasing piston bore, Subaru aimed to reduce emissions and improve fuel economy, while increasing and broadening torque output over the previous generation engine. The FB has an all new block and head featuring dual overhead cams with intake and exhaust variable valve timing (AVCS - Active Valve Control System), and a timing chain that replaced the timing belt. Moving to chain-driven cams allows the valves to be placed at a more narrow angle to each other and shrinks the cylinder bore from 99.5 mm to 94. It results in less unburned fuel during cold start, thereby reducing emissions. Subaru also uses asymmetrical connecting rods like those in EZ36. The FB is only marginally heavier and has similar exterior dimensions compared to an EJ engine of equivalent displacement. In Jan 2011, Car and Driver was told direct injection would be added soon. Direct Injection was added to FB engines used in the 2017 Impreza, 2018 Crosstrek, 2019 Forester and the 2020 Legacy and Outback models. Subaru claims a 28-percent reduction in friction losses, mainly due to lighter pistons and connecting rods. The FB has a 10% improvement in fuel economy with the power coming on sooner and the torque band being broader.

Subaru CB engine

The CB engine was first introduced in 2020 with the second-generation Levorg. According to Subaru, CB stands for Concentration/Compact Boxer. The first engine in the series is designated CB18, a 1.8 litre dual overhead cam 16-valve engine featuring dual AVCS with gasoline direct injection and a turbocharger. Bore and stroke are 80.6 ×, respectively, and the compression ratio is 10.4:1. Rated output power is 130 kW at 5,200–5,600 RPM and torque is 300 Nm at 1,600–3,600 RPM. Compared to the FB16 used in the previous generation of the Levorg, the CB18 offers decreased fuel consumption (16.6 km/L for the CB18 and 16.0 km/L for the FB16, both using the JC08 mode) and increased torque (300 Nm for the CB18 and 250 Nm for the FB16). In addition, the CB16 achieves its peak torque at a lower engine speed. The CB18 also is shorter and lighter than the FB16; the bore pitch (centerline to centerline spacing between adjacent cylinders) has decreased from 113.0 to 98.6 mm, the overall crank length has decreased from 350.5 to 315.9 mm, and engine weight has been reduced by 14.6 kg. For the first time in a Subaru engine, the centerlines of the cylinder bores do not intersect with the crankshaft axis to reduce friction during the piston downstroke; instead, there is a crank offset of 8 mm. Overall thermal efficiency is 40% due to the adoption of lean-burn combustion with an excess air ratio (λ) of 2.

Six-cylinder

All of Subaru's six-cylinder engines are of a liquid-cooled, Flat-6 four-stroke design.

Subaru ER engine

**** Subaru**** introduced**** its first six-cylinder**** engine**** in**** its Subaru**** XT**** sports**** car.**** This MPI SOHC 2-Valve engine was based on the EA82, with two cylinders added to the front.

Subaru EG engine

The **** engine**** was a direct**** replacement for the ER**** engine****.**** The ER had been used only in the Subaru XT6, which was being replaced by the Subaru Alcyone SVX, and the company took the opportunity to create a new engine based on the more modern EJ rather than the EA engine series. As the ER27 was to the EA82, Subaru took the EJ22 design and created a six-cylinder version to make the new EG33. However, this four-valves-per-cylinder engine was DOHC, and valvetrain parts came from the not yet released EJ25D. Bore: 96.9 mm Stroke: 75 mm

Subaru EZ engine

The **** was introduced**** in**** 1999**** in**** the Japanese**** market****,**** in**** the Subaru**** Outback,**** and in**** 2000**** in**** the United**** States**** market****,**** also**** in**** the Outback.**** It is a flat-six, 24-valve, quad-cam engine with an aluminium block and heads. It is available in EZ30 and EZ36 variants. Though the second iteration of the EZ30D used from 2003 to 2009 was heavily updated from the early EZ30D used from 2001 to 2003, Subaru continued to identify it as EZ30D. "EZ30R" is a false engine code often used on the Internet for the later EZ30, but Subaru has never used it as an official engine code. All EZ-series engines use dual timing chains and feature coil-on-plug ignition. The 2000-2003 EZ30D used one exhaust port per head, a cable-actuated throttle, variable intake geometry, and a cast aluminium intake manifold. It was only available with an automatic transmission. The 2003-2007 EZ30D received new cylinder heads with 3 exhaust ports per head, AVLS, AVCS on the intake cams only, a drive-by-wire throttle, and a plastic intake manifold. It was available in manual and automatic unlike the original EZ30D. The EZ36D retains the plastic intake manifold, 3 exhaust ports per head, and drive-by-wire throttle of the later EZ30D, but loses AVLS while gaining AVCS for both intake and exhaust cams. The EZ36D also incorporates an asymmetrical connecting rod design shared with the FB series of engines and the EE20 diesel engine.