Subaru Engine Codes Explained: Complete Guide to Understanding Subaru’s Engine Designation System

Subaru Motor Corporation, operating as the automotive manufacturing division of Subaru Corporation (formerly Fuji Heavy Industries), has established itself as a distinctive presence in the global automotive market through engineering philosophies and design choices that differentiate the brand from mainstream competitors. The company’s commitment to horizontally-opposed boxer engine configurations across nearly its entire product line, the widespread adoption of symmetrical all-wheel drive as standard equipment rather than optional enhancement, and the cultivation of passionate enthusiast communities around performance models like the WRX and STI have created brand identity and customer loyalty rivaling any automaker despite Subaru’s relatively modest production volumes.

Central to understanding Subaru vehicles—whether conducting maintenance, sourcing replacement parts, researching vehicle history, or diagnosing problems—is familiarity with Subaru’s engine designation system. Unlike some manufacturers using seemingly arbitrary alphanumeric codes providing minimal information without reference materials, Subaru’s engine codes follow logical structures encoding meaningful information about engine families, displacement, and configuration directly into code formats. This systematic approach enables informed enthusiasts and professional technicians to immediately extract essential engine characteristics from code designations appearing on engine blocks, service documentation, and parts catalogs.

However, Subaru’s engine coding system has evolved substantially across the company’s history, with different eras employing varied designation schemes and with code meanings shifting as engine technologies advanced and model lineups expanded. The EK-series two-cylinder engines powering early Subaru 360 microcars used different coding logic than the EJ-series four-cylinder boxers dominating Subaru’s lineup from 1989 through the 2010s, while modern FB and FA engine families represent yet another designation evolution. Understanding these historical progressions and recognizing how to decode various code formats enables comprehensive Subaru knowledge spanning the company’s entire production history.

This comprehensive guide examines Subaru’s engine code structure and decoding methodology, details each major engine family from the 1950s-era EK series through modern FB/FA platforms, explains the specific code variations within families indicating displacement and configuration differences, provides historical context about when engines were introduced and which models used them, and establishes practical applications for engine code knowledge supporting maintenance, parts sourcing, and vehicle identification.

Understanding Subaru Engine Code Structure

Subaru’s engine designation system follows consistent logic encoding engine family, displacement, and configuration information into compact alphanumeric codes typically comprising 4-5 characters.

Basic Code Format and Component Meanings

The standard Subaru engine code structure consists of:

Position 1 (Always “E”): Indicates “Engine”—all Subaru engine codes begin with E, distinguishing engine codes from transmission codes (beginning with different letters) or other component identifiers.

Position 2 (Letter): Identifies the engine family or series. This letter groups related engines sharing fundamental architecture, bore and stroke relationships, and design generation. Examples include A (EA series), J (EJ series), K (EK series), F (EF series), E (EE series), L (EL series), N (EN series), Z (EZ series), and more recently B (FB series) and A (FA series in modern context).

Positions 3-4 (Numbers): Indicate engine displacement in deciliters (tenths of a liter). An EJ25 uses 2.5 liters displacement (25 deciliters), while an EJ20 uses 2.0 liters (20 deciliters). This two-digit displacement code provides immediate recognition of engine size—critical information for parts compatibility, performance expectations, and vehicle identification.

Position 5 (Optional Letter or Number): Denotes specific configuration variations within the displacement family including turbocharging (T suffix), fuel injection type, valvetrain configuration (DOHC vs SOHC), or generational revisions. Not all engines use this fifth character, with naturally aspirated base engines often carrying just four-character designations.

Examples Demonstrating Code Structure

EJ257: Breaking down this code reveals E (engine), J (EJ family—the four-cylinder boxer series introduced 1989), 25 (2.5 liter displacement), 7 (seventh major revision of the EJ25, used in 2004-2007 WRX STI with specific turbocharging and internals).

EJ205: Similarly decodes as E (engine), J (EJ family), 20 (2.0 liter displacement), 5 (fifth major revision used in 2002-2005 WRX with TD04 turbocharger).

FB25: Modern engine designation showing E has been dropped in recent usage, with FB (new FB series introduced 2010), 25 (2.5 liter displacement). The absence of additional suffix indicates naturally aspirated base configuration.

FA20DIT: Decodes as FA (FA series—direct injection turbocharged boxer introduced 2012), 20 (2.0 liter displacement), DIT (Direct Injection Turbo—specific designation for turbocharged version used in WRX).

Historical Evolution of Code Systems

Early Subaru engines (1950s-1960s) used simpler two or three-character codes before the standardized E-prefix system was fully established. As Subaru’s product line expanded and engine families proliferated, the need for more systematic designation schemes drove evolution toward the current format.

The E-prefix standardization occurred during the 1970s-1980s as Subaru transitioned from small two-cylinder engines to larger four-cylinder boxers and began exporting vehicles internationally. The standardized system enabled clearer communication across markets and simplified parts cataloging as model diversity increased.

Modern simplification has seen the E-prefix sometimes dropped in marketing materials and casual reference (referring to “FB25” rather than “EFB25”), though technical documentation often retains the full designation. This evolution reflects familiarity with Subaru’s system among enthusiasts and professionals who no longer require the E-prefix for context.

The EK Series: Subaru’s Two-Cylinder Pioneer Engines (1958-1990)

The EK engine family powered Subaru’s earliest production vehicles, establishing the company’s presence in Japan’s emerging kei car market during the post-war economic recovery.

EK Series Overview and Historical Context

The EK designation indicated Subaru’s first production engines, with K representing the family designation for these compact two-cylinder powerplants. The series spanned from 1958 when the Subaru 360 microcar launched through 1990 when the last EK-powered Sambar kei trucks were replaced by more modern inline-four EN series engines.

Two-stroke origins characterized early EK engines, reflecting common practice for small-displacement engines of the era where two-stroke simplicity and power density suited microcar applications despite higher emissions and oil consumption compared to four-stroke alternatives. The transition to four-stroke EK engines during the 1970s reflected evolving emission regulations and customer preferences for reduced noise, smoke, and fuel consumption.

Air-cooled and water-cooled variants existed within the EK family, with earlier engines using air-cooling (simpler, lighter, but less effective at maintaining consistent operating temperatures) while later versions adopted water-cooling (more complex but providing better temperature control and reduced noise).

EK31 Series: The Original Subaru 360 Engine

The EK31 represented Subaru’s first production automotive engine, powering the revolutionary Subaru 360 microcar introduced in 1958. This tiny two-stroke, air-cooled twin displaced just 356cc (hence the “360” name reflecting rounded displacement), producing approximately 16 horsepower—modest even by 1950s standards but adequate for the 900-pound vehicle navigating Japan’s crowded urban streets.

The Subaru 360 achieved remarkable success despite its diminutive specifications, becoming Japan’s best-selling car during the 1960s and earning the nickname “Ladybug” from its rounded styling. The 360’s affordability, fuel efficiency (achieving 50+ mpg), and ability to navigate narrow Japanese roads made it ideal transportation during Japan’s economic growth period when car ownership transitioned from luxury to necessity for middle-class families.

Export versions including the Subaru 360 sold in the United States (1968-1970) used the same EK31 engine, though the car’s performance proved marginal for American highway speeds and the vehicle’s small size raised safety concerns. Despite limited U.S. market success, the 360 established Subaru’s presence in North America and demonstrated the company’s engineering competence.

The EK31’s service in the original Subaru Sambar kei truck (1961-1970) demonstrated the engine’s versatility beyond passenger car applications, with the small truck becoming popular for commercial and agricultural use in Japan where full-size trucks were impractical for many operations.

EK32 and EK33: Performance and Evolution

The EK32 represented a performance evolution of the EK31, introduced in the Subaru 360 Young SS (1968-1970)—a sporting version with increased compression and tuning producing approximately 20 horsepower. While the 25% power increase seems modest, it represented substantial improvement in the microcar context, enabling livelier acceleration and slightly higher top speeds.

The EK33 continued EK evolution with further refinements appearing in the Subaru R-2 (1969-1971) and updated Sambar models (1970-1973). These engines maintained the two-stroke, air-cooled configuration while incorporating improved reliability and reduced emissions compared to earlier versions as Japanese regulations began addressing automotive air pollution.

EK34: Water-Cooling Transition

The EK34 marked a significant technological transition, adopting water-cooling while retaining two-stroke operation. This hybrid approach provided improved thermal management compared to air-cooling while avoiding the complexity of immediate transition to four-stroke architecture.

Applications included the Subaru R-2 (1971-1972), later Sambar models (1973-1976), and the original Subaru Rex (1972-1973). The water-cooling improved reliability, reduced noise, and enabled more consistent performance, though the two-stroke configuration still produced characteristic smoke and required oil-fuel mixing creating inconvenience for owners.

EK21, EK22, EK23: Four-Stroke Modernization

The transition to four-stroke operation with the EK21 (1976) reflected regulatory pressure and customer preference driving Japanese manufacturers away from two-stroke engines. Four-stroke engines offered cleaner combustion, elimination of oil-fuel mixing requirements, reduced smoke and noise, and improved fuel economy offsetting the added complexity.

The EK21 and EK22 served brief transitional roles in Rex and Sambar models during 1976-1977, quickly supplanted by the more advanced EK23 becoming the standard four-stroke EK variant.

The EK23 achieved remarkable longevity, serving from 1977 through 1990 in Sambar trucks and through 1989 in Rex kei cars. Various EK23 iterations included:

EK23 base: Naturally aspirated with conventional two-valve heads used in standard Sambar and Rex models producing approximately 30-37 horsepower depending on tuning.

EK23 Three-Valve: Advanced version with three valves per cylinder (two intake, one exhaust) improving breathing and power output to approximately 40-42 horsepower while maintaining fuel efficiency. Used in sporting Rex Viki models (1986-1989) and later Sambar applications (1989-1990).

EK23 Turbo: Turbocharged version for performance Rex Combi models (1983-1986) producing approximately 41-45 horsepower—impressive output from 550cc displacement and remarkable for kei car regulations.

EK23 Three-Valve Turbo: Combining three-valve technology with turbocharging in Rex VX models (1986-1989), achieving peak kei car performance with approximately 50-52 horsepower from just 550cc.

EK23 Three-Valve Supercharger: Alternative forced induction using mechanical supercharging (1988-1989) providing immediate throttle response compared to turbo lag, producing similar power to turbocharged versions.

EK42 and Later Variants

The EK42 represented displacement increases within kei car regulations as those regulations evolved, allowing larger engines (660cc from original 550cc limits) during the late 1980s-early 1990s. The EK42 served in Sambar/700 and Rex models bridging to the newer EN inline-four series that ultimately replaced all EK engines by 1990.

The EF Series: Three-Cylinder Progression (1984-1992)

The EF family represented Subaru’s three-cylinder engine development, filling displacement gaps between two-cylinder EK engines and four-cylinder EA/EJ families.

EF Series Development and Purpose

The EF introduction around 1984 provided Subaru with efficient three-cylinder options for kei cars and small export models where two-cylinder engines proved inadequate but four-cylinder engines were unnecessarily large and heavy. The three-cylinder configuration balanced smoothness (better than two-cylinder) with compactness and efficiency (better than four-cylinder) for specific applications.

The liquid-cooled, four-stroke design with SOHC valve actuation represented modern architecture compared to earlier air-cooled two-strokes, providing refinement appropriate for evolving customer expectations and emission regulations.

EF10 and EF12: Justy Powerplants

The EF10 (nominally 1.0 liter displacement, actually 997cc from 70mm bore × 68.4mm stroke) produced approximately 50-55 horsepower in base form, providing adequate power for the lightweight Subaru Justy subcompact introduced in 1984.

The EF12 (nominally 1.2 liter, actually 1,189cc from 76mm bore × 68.4mm stroke) offered increased displacement producing approximately 66-73 horsepower depending on market and emissions tuning. The EF12 served in later Justy models and some export markets where the larger displacement provided more competitive performance.

Both EF engines featured two valves per cylinder, belt-driven overhead camshafts, and electronic fuel injection (on most markets, though some retained carburetors). The engines’ all-aluminum construction kept weight minimal—critical for small car performance and fuel economy.

The EF series’ service life extended through 1992 when Justy production ended for most markets (continuing longer in some regions with updated models). The engines earned reputations for reliability and fuel economy, with many examples exceeding 200,000 miles with proper maintenance despite their small displacement and relatively high specific output for the era.

The EA Series: Subaru’s First Four-Cylinder Boxer Engines (1966-1994)

The EA engine family established Subaru’s signature boxer four-cylinder architecture, serving across nearly three decades in progressively larger displacements powering Subaru’s transition from microcar manufacturer to mainstream automaker.

EA Series Overview and Boxer Architecture

The EA designation indicated Subaru’s first production four-cylinder boxer engines, with A representing the family designation that would later be followed by the similar but more advanced EJ series. The horizontal opposed (boxer) configuration positioned cylinders horizontally on opposite sides of the crankshaft, creating inherently balanced designs with low centers of gravity and compact installation dimensions.

Boxer engine advantages include perfect primary and secondary balance (with 180-degree crank phasing), low center of gravity improving vehicle handling and stability, compact height enabling lower hood lines and better crash structure packaging, and distinctive exhaust notes differentiating Subarus from inline or V-configuration competitors.

The EA series spanned from the 1966 introduction of the EA52 (Subaru 1000’s 977cc engine) through 1994 when the final EA82-powered Loyales ended production. This remarkable longevity reflected continuous evolution and the architecture’s fundamental suitability for Subaru’s product positioning.

EA52: The First Boxer Four

The EA52 (977cc from 72mm bore × 60mm stroke) powered the groundbreaking Subaru 1000—the company’s first four-cylinder car and first model targeting export markets beyond Japan. The water-cooled, four-stroke boxer produced approximately 55 horsepower, providing competitive performance for compact sedans of the mid-1960s.

The Subaru 1000’s significance extended beyond simply having four cylinders—it established front-wheel drive (unusual for 1966), boxer engine layout, and quality standards enabling Subaru’s evolution from microcar specialist to mainstream manufacturer. The EA52’s reliability in this groundbreaking model validated Subaru’s boxer architecture for future development.

EA61, EA62, EA63: Displacement Growth

The EA61 (1,088cc from 76mm bore × 60mm stroke) appeared in 1970, providing incrementally increased displacement for improved power and torque. The modest increase to approximately 60-65 horsepower suited growing vehicle sizes and customer expectations for performance.

The EA62 (1,267cc from 82mm bore × 60mm stroke) continued displacement expansion in the early 1970s, producing approximately 70-80 horsepower depending on market and emissions specifications. This displacement supported larger models like the Leone (DL, GL, GL-10 in various markets).

The EA63 (1,361cc from 85mm bore × 60mm stroke) represented further growth reaching approximately 1.4 liters, though this variant saw limited production compared to the more common EA71 that followed.

EA71: Widespread 1.6L Application

The EA71 (1,595cc from 92mm bore × 60mm stroke) became Subaru’s volume engine through much of the 1970s, powering various Leone models and establishing 1.6 liter displacement as Subaru’s standard offering across many markets. Power output ranged from approximately 67 horsepower in emissions-strangled U.S. specifications to 80+ horsepower in less restrictive markets.

The EA71 featured carburetor fuel delivery on most applications (though some later versions received electronic fuel injection), single overhead camshafts, and conventional points ignition evolving to electronic ignition as electronics became standard. The engine earned reputation for durability despite modest power outputs and relatively simple technology.

EA81: The 1.8L Standard

The EA81 (1,781cc from 92mm bore × 67mm stroke) introduced in 1980 became Subaru’s mainstream engine through the 1980s, powering Leone, GL, DL, and Loyale models across global markets. The stroke increase from EA71 provided improved low-end torque while retaining good high-RPM power, producing approximately 71-84 horsepower depending on market specifications.

The EA81 represented substantial refinement over earlier EA engines including more durable timing belt systems (replacing chains on some earlier engines), improved sealing and reduced oil consumption, better emissions control meeting increasingly stringent regulations, and enhanced serviceability through improved component access.

Applications included:

• Subaru Leone/DL/GL (1980-1984 in most markets)
• First-generation Subaru Brat pickup (1978-1981)
• Early Subaru XT/GL-10 coupe (1985-1987 base models)

EA81T: Turbocharging Arrives

The EA81T added turbocharging to the EA81 platform, representing Subaru’s first turbocharged production engine. The addition of a small turbocharger (IHI RHB5 typically) increased output to approximately 94-100 horsepower—a 20-30% gain enabling considerably improved performance.

Applications included:

• Subaru GL-10 Turbo (1984-1985)
• Subaru XT/Alcyone Turbo (1985-1987)
• First generation Subaru RX Turbo (1985-1989 in various markets)

The EA81T established turbocharged Subaru as viable performance alternative to larger-displacement competitors, previewing the company’s future direction toward turbocharged performance models culminating in legendary WRX and STI variants.

EA82: Final EA Evolution

The EA82 (1,781cc maintaining EA81 dimensions) represented comprehensive redesign rather than simple evolution, introducing dual overhead camshafts (DOHC on some versions, SOHC on others), hydraulic valve lash adjusters (eliminating periodic valve adjustments), improved breathing and combustion chamber design, and multi-point fuel injection across most applications.

Power output improved to approximately 90-97 horsepower naturally aspirated—matching or exceeding turbocharged EA81T output through improved efficiency rather than forced induction. The refinement extended to reduced noise and vibration, improved fuel economy, and enhanced reliability.

Applications included:

• Subaru GL, DL, Loyale (1985-1994)
• Later Subaru XT coupe (1987-1991)
• Second generation Subaru RX (1986-1989)
• Later Subaru Brat/Brumby (1985-1987)

EA82T: Turbocharged MPFI Performance

The EA82T added turbocharging to the modern EA82 architecture, producing approximately 111-115 horsepower—a substantial increase enabling genuine performance credentials. The combination of MPFI fuel injection, DOHC valvetrain, and turbocharging created responsive, flexible power delivery that contemporary reviews praised for exceeding expectations given modest displacement.

Applications included:

• Subaru XT Turbo/XT6 (turbocharged four-cylinder versions, 1987-1991)
• Subaru RX Turbo (1986-1989)
• Various Japanese domestic market models with turbocharging

The EA82T served as direct predecessor to the legendary EJ20T used in first-generation WRX, establishing engineering foundations and market positioning enabling Subaru’s performance reputation.

The EE Series: Subaru’s Diesel Introduction (2008-2020)

The EE family represented Subaru’s first horizontally-opposed diesel engine, developed specifically for European markets where diesel powertrains dominated sales in many segments.

EE20: Boxer Diesel Innovation

The EE20 (1,998cc from 86mm bore × 86mm stroke—perfectly square design) debuted at the 2007 Geneva Motor Show, generating substantial interest as the first boxer diesel entering passenger car production. The engine featured common-rail direct injection at remarkably high 180 MPa (26,100 psi) rail pressure, four valves per cylinder with DOHC, twin-turbochargers on some versions (single turbo on others), and five main bearings providing crankshaft rigidity essential for diesel’s higher cylinder pressures.

Power and torque varied by application and model year but typically ranged from 145-150 horsepower with 258-280 lb-ft torque—impressive torque output nearly double that of similar-displacement gasoline engines, though peak power remained modest by modern turbocharged gasoline standards.

Development timeline extending three years from project initiation to production (relatively rapid for all-new engine architecture) reflected Fuji Heavy Industries’ commitment to European market expansion where diesel absence placed Subaru at competitive disadvantage.

Applications included:

• Subaru Legacy (sedan and wagon, 2008-2020 in Europe)
• Subaru Outback (2008-2020 in Europe)
• Subaru Forester (2012-2020 in Europe)
• Subaru Impreza (limited availability, certain markets)

The EE20 never entered production for North American markets where diesel passenger cars gained minimal market share and where Subaru’s traditional gasoline boxer engines aligned better with customer preferences and corporate average fuel economy strategies.

EE20 Performance and Reliability

Fuel economy represented the EE20’s primary advantage, achieving 35-45 mpg combined in real-world driving across Legacy, Outback, and Forester applications—approximately 30-40% better than equivalent gasoline models. In European markets where fuel costs substantially exceeded U.S. prices and taxation favored diesel efficiency, these economy figures provided genuine ownership cost advantages.

Reliability proved mixed through the EE20’s production life. Early examples suffered problems including DPF clogging (common diesel issue but particularly problematic given Subaru’s limited diesel experience), EGR system failures causing loss of power and expensive repairs, timing belt failures if service intervals weren’t meticulously followed (shorter than gasoline boxer intervals), and injector failures from fuel quality issues.

Later production EE20 engines (approximately 2012 onwards) demonstrated improved reliability as Subaru refined emission control systems and extended warranty coverage addressing owner concerns. However, the engine never achieved the legendary durability reputation of Subaru’s gasoline boxers, limiting enthusiasm among the Subaru faithful.

EE20 Discontinuation

Production ended around 2020 as increasingly stringent European emission regulations (Euro 6d requirements) made diesel passenger car compliance increasingly expensive while hybridization offered alternative efficiency pathways better aligned with regulatory trajectories. Subaru’s limited diesel volumes couldn’t justify investments necessary for next-generation compliance, leading to strategic withdrawal from diesel powertrains.

The EJ Series: Legendary Performance Engines (1989-Present)

The EJ engine family represents Subaru’s most significant and longest-serving engine architecture, powering everything from economy sedans to legendary WRX and STI performance models that established Subaru’s reputation among driving enthusiasts globally.

EJ Series Development and Architecture

The EJ introduction in 1989 coincided with the first-generation Legacy launch, representing comprehensive redesign compared to EA predecessors. The new architecture featured four valves per cylinder (compared to EA’s two valves), five main bearings for improved crankshaft rigidity, belt-driven dual overhead camshafts, and from the start, design accommodation for turbocharging and performance applications.

The designation logic follows standard Subaru practice: EJ indicates the engine family, followed by displacement in deciliters (EJ20 = 2.0L, EJ25 = 2.5L), with optional suffix digits indicating specific revisions and the T suffix indicating turbocharging.

Key EJ variants span from economy 1.5L naturally aspirated engines producing 100 horsepower to highly-tuned 2.5L turbocharged STI engines producing 300+ horsepower—remarkable diversity within a single architecture demonstrating the platform’s flexibility and scalability.

EJ15: Entry-Level 1.5L

The EJ15 (1,493cc from 92mm bore × 56mm stroke—unusually undersquare for performance potential) served entry-level applications across various markets from 1990 through the mid-2000s. Power output ranged from approximately 90-100 horsepower depending on market emissions standards and tuning.

Applications included:

• Base Subaru Impreza (1993-2006 in various markets)
• Entry-level Legacy (1989-1998 in some markets)
• Various Japanese domestic market economy versions

The EJ15 offered adequate performance for small car applications while delivering excellent fuel economy (30+ mpg combined typical) making it popular in markets where tax structures favored smaller-displacement engines.

EJ16: Short-Lived 1.6L Variant

The EJ16 (1,595cc from 92mm bore × 60mm stroke) provided slightly increased displacement and power (approximately 110-115 horsepower) in select markets during 1993-2006. The variant saw limited application primarily in European and Asian markets where 1.6L displacement aligned with insurance or tax brackets creating customer preference.

EJ18: Economy 1.8L Option

The EJ18 (1,820cc from 92mm bore × 68.4mm stroke) served primarily Japanese domestic market and European applications in Impreza and Legacy models during the 1990s. Power output of approximately 115-125 horsepower positioned the EJ18 between economy EJ15/EJ16 variants and mainstream EJ20 versions.

Limited North American presence reflected the market’s preference for larger displacement engines where the modest power and torque advantages over EJ15/EJ16 didn’t justify separate model offerings when the substantially more powerful EJ22 and EJ25 served volume applications.

EJ20: The Legendary 2.0L Platform

The EJ20 represents perhaps the most significant single engine code in Subaru history, spanning naturally aspirated and turbocharged versions, powering millions of vehicles across all major markets, and enabling legendary performance in WRX, STI, and other applications.

EJ20 variants include:

EJ20E/EJ20G (Early Naturally Aspirated): Base versions producing approximately 130-150 horsepower in Legacy, Impreza, and Forester applications through the 1990s-early 2000s.

EJ20K: Higher-output naturally aspirated version (approximately 155-160 horsepower) using revised cams, compression, and tuning in sportier applications.

EJ205 (WRX 2002-2005): Turbocharged version producing approximately 227 horsepower (North American specification) with TD04 turbocharger, top-mount intercooler, and ECU tuning optimized for midrange torque. This engine powered the first North American WRX (2002-2005), creating Subaru’s performance legend in the U.S. market.

EJ207 (JDM STI): Higher-performance turbocharged version producing 280-320 horsepower depending on version (Japanese manufacturers voluntarily limited advertised output to 280 hp through early 2000s though actual output often exceeded ratings). The EJ207 featured forged pistons, sodium-filled exhaust valves, larger IHI turbocharger (VF series), and aggressive tuning enabling remarkable specific output exceeding 150 hp/L.

EJ208 (JDM WRX STI Spec C): Ultra-high-performance variant for track-focused STI Spec C models, featuring titanium valves, further strengthened internals, and tuning producing 320+ actual horsepower.

EJ22: North American Workhorse

The EJ22 (2,212cc from 96.9mm bore × 75mm stroke) became Subaru’s mainstream North American engine through the 1990s, powering Legacy, Impreza, and Baja models with naturally aspirated output of approximately 130-142 horsepower depending on generation and tuning.

The EJ22’s reputation for near-bulletproof reliability exceeds even Subaru’s generally strong reliability, with many examples exceeding 300,000-400,000 miles with minimal maintenance beyond routine servicing. The understressed nature (relatively conservative specific output around 60 hp/L), robust bottom end, and simple naturally aspirated configuration contributed to legendary durability.

Applications included:

• Subaru Legacy (1990-2001)
• Subaru Impreza (1993-2001 base models)
• First generation Subaru Forester (1998-2002)
• Subaru Baja (2003-2006 base model)

EJ22T (Turbocharged): Limited-production turbocharged variant producing approximately 165-200 horsepower in Japanese domestic market Legacy RS models and select other applications. The EJ22T served as predecessor to more famous EJ20 and EJ25 turbocharged engines.

EJ25: Modern Subaru’s Standard

The EJ25 (2,457cc from 99.5mm bore × 79mm stroke) became Subaru’s mainstream engine from the mid-1990s onward, replacing EJ22 in most North American applications and powering countless Legacy, Outback, Impreza, and Forester models.

Naturally aspirated EJ25 variants produced approximately 165-180 horsepower depending on generation, providing substantially improved torque compared to smaller EJ engines—critical for growing vehicle weights and customer expectations for effortless performance.

The EJ25’s service continues in some current Subaru models (though newer FB25 increasingly replaces it), demonstrating the architecture’s longevity and continued relevance despite being fundamentally 1980s design.

Notable EJ25 variants:

EJ251/EJ252/EJ253 (SOHC Naturally Aspirated): Base engines in Outback, Forester, Legacy, and Impreza producing 165-175 horsepower, known for head gasket problems on 1997-2011 examples requiring preventative maintenance or eventual replacement.

EJ255 (WRX 2006-2014): Turbocharged version producing approximately 224-265 horsepower depending on generation, replacing earlier EJ205 in WRX with increased low-end torque though some enthusiasts preferred earlier 2.0L’s higher-RPM character.

EJ257 (STI 2004-Present): High-performance turbocharged variant producing 300-310 horsepower in U.S.-specification STI models, featuring semi-closed deck block, forged pistons, sodium-filled exhaust valves, and IHI VF-series turbochargers. This engine powered every U.S.-market WRX STI from introduction through current generation.

EJ257’s legendary status stems from power capability (easily modified to 400-500+ horsepower with supporting modifications), durability under performance use (when properly maintained and not abused), and motorsport success (numerous championships in rally, time attack, and other competition).

EJ25 Reliability Concerns

Head gasket failures affected most SOHC EJ25 variants (EJ251/EJ252/EJ253) produced from approximately 1997-2011, with external coolant leaks developing typically at 60,000-120,000 miles requiring expensive repairs ($1,500-2,500 typically for professional service including machining and parts).

The cause involved head gasket material incompatibility with coolant chemistry and thermal cycling patterns, with revised Multi-Layer Steel (MLS) gaskets introduced around 2011-2012 substantially improving reliability.

Turbocharged EJ25 variants (EJ255/EJ257) using different head gasket designs avoided the epidemic failures affecting naturally aspirated versions, though they introduced different concerns including ringland failures on EJ257 under detonation conditions.

EJ30: The Unique Six-Cylinder Boxer

The EJ30 (2,999cc, actually six-cylinder rather than four-cylinder despite EJ designation) represents Subaru’s rarest boxer engine—a horizontally-opposed six-cylinder offering smoothness exceeding four-cylinder engines while maintaining boxer packaging advantages.

The flat-six configuration provided inherent balance surpassing four-cylinder boxers (no unbalanced primary or secondary forces whatsoever), extremely smooth operation rivaling inline-six or V12 engines, and distinctive character differentiating upmarket Subaru models from mainstream offerings.

Applications limited to:

• Subaru Alcyone SVX (1991-1997)—luxury sport coupe with distinctive window-within-window glass design
• Limited Japanese domestic market Legacy variants

Power output of approximately 230-240 horsepower provided strong performance, though the engine’s weight and complexity prevented widespread adoption. The EJ30’s rarity makes it highly sought by certain Subaru enthusiasts despite limited mainstream impact.

The EL Series: EJ Evolution (2006-Present)

The EL designation represented evolutionary development of EJ architecture, though with sufficient changes to warrant new family designation.

EL15: Replacing EJ15

The EL15 (1,498cc maintaining EJ15 dimensions) replaced earlier EJ15 engines in Japanese domestic market Impreza 1.5R models beginning around 2006. The engine featured updated engine management, improved emissions compliance, and minor refinements while sharing substantial architecture with EJ predecessors.

Power output of approximately 110 horsepower matched later EJ15 versions while meeting more stringent emissions regulations and improving fuel economy through refined engine management and reduced friction.

The EL designation saw limited application compared to widespread EJ use, primarily serving JDM and select Asian markets where 1.5L displacement remained popular. The engine continues in some current models though specific variants and production volumes are limited.

The EN Series: Kei Car Four-Cylinder (1988-Present)

The EN engine family represented Subaru’s transition from two-cylinder EK engines to more refined four-cylinder power for kei car applications.

EN Series Development

The EN07 introduced in 1988 represented Subaru’s first production inline-four engine (departing from boxer architecture for space efficiency in tiny kei trucks and vans where boxer width disadvantaged packaging).

The EN series uses inline-four rather than boxer configuration, water-cooling, SOHC or DOHC depending on variant, and displacements of 658cc (meeting Japanese kei car regulations) across numerous variations.

Applications include all modern Sambar kei trucks and vans, as well as other kei vehicles in Japanese market. The engine continues in current production serving commercial vehicle applications.

Modern Engine Families: FB, FA, and Beyond

Subaru’s most recent engine developments introduced new architecture addressing fuel economy, emissions, and performance requirements that evolved EJ platforms couldn’t fully meet.

FB Series: Naturally Aspirated Efficiency

The FB engine (introduced 2010) represented clean-sheet design incorporating decades of boxer experience while adopting technologies including chain-driven DOHC (eliminating timing belt maintenance), direct injection (on some variants), improved thermal management, and reduced friction through numerous detail improvements.

FB20 (1,995cc): Powering base Impreza, Crosstrek, and Forester models with approximately 148-152 horsepower and improved fuel economy versus predecessor EJ20.

FB25 (2,498cc): Serving mainstream Legacy, Outback, and Forester applications with approximately 175-182 horsepower and substantially improved economy versus EJ25.

The FB series continues expanding through Subaru’s lineup, though enthusiasts sometimes lament the loss of EJ character despite FB’s objective improvements in efficiency and refinement.

FA Series: Turbocharged Performance

The FA20DIT (1,998cc with Direct Injection Turbo) powers current WRX models (2015-present in most markets) with approximately 268-271 horsepower—substantial improvement versus earlier EJ255 despite similar displacement.

The FA20 naturally aspirated variant (without DIT designation) serves Toyota 86 / Subaru BRZ sports cars with approximately 200-228 horsepower depending on generation, representing Subaru’s collaboration with Toyota producing affordable rear-drive sports car.

Diagnostic Code Reading: Subaru OBD Systems

Beyond engine designation codes stamped on blocks, Subaru vehicles store diagnostic trouble codes providing essential information for troubleshooting problems.

Pre-OBD2 Diagnostic Systems (1985-1995)

Early Subaru diagnostic systems used proprietary methods for code retrieval without requiring scan tools:

Read Memory connectors typically located under dash near fuse panel, allowed jumper connection forcing ECU to flash stored codes using Check Engine light or dedicated oxygen monitor light.

Flash code patterns used long pulses (1.2 seconds) representing tens and short pulses (0.2 seconds) representing ones, separated by pauses. For example, Code 12 displayed as one long pulse, pause, two short pulses.

Code 12 appeared as system normal indication during diagnostic mode (distinct from true fault codes), confirming successful test mode entry and providing baseline ensuring technicians correctly interpreted subsequent codes.

Test mode procedures varied slightly by model year and system, but generally involved:

1. Locating diagnostic connectors (typically two pairs—”Read Memory” and “Test Mode”)
2. Connecting appropriate jumper wires
3. Turning ignition on without starting
4. Observing flash codes on dashboard indicator
5. Recording codes for reference
6. Clearing codes after repairs by connecting both connector pairs with warm engine

OBD2 Systems (1996-Present)

1996 onwards Subaru vehicles use standardized OBD2 systems requiring scan tools for code reading, though some models retain flash code capability for basic diagnosis without tools.

Standard OBD2 procedures involve:

1. Connecting scan tool to OBD2 port (typically under dash near steering column)
2. Turning ignition on
3. Reading stored codes (P-codes: P0XXX through P3XXX format)
4. Interpreting codes using databases or service information
5. Clearing codes after repairs using scan tool

1995 Impreza and Legacy represented transitional models using early OBD2 systems while retaining flash code capability for basic diagnostics—useful feature when scan tools aren’t available.

Practical Applications of Engine Code Knowledge

Understanding Subaru engine codes enables numerous practical applications for owners, technicians, and enthusiasts.

Parts Sourcing and Compatibility

Engine code knowledge allows accurate parts identification ensuring compatibility. Components like pistons, connecting rods, cylinder heads, camshafts, and numerous engine-specific parts vary between engine codes requiring precise identification for proper replacement.

Interchangeability between related engines (e.g., various EJ25 variants) follows logical patterns based on code understanding—turbocharged and naturally aspirated versions share many components while differing in forced induction systems, while different generations within families may use updated parts requiring verification.

Vehicle Identification and History

Engine codes help verify vehicle authenticity and modification history. Confirming that an advertised “WRX STI” actually contains the correct EJ257 rather than base EJ25 prevents fraud, while identifying swapped engines helps assess modification quality and potential reliability impacts.

Performance Modification Planning

Understanding engine families guides modification planning. Knowing that EJ257 uses semi-closed deck blocks suitable for high boost while EJ255 uses open-deck designs with lower power limits affects turbo upgrade decisions. Recognizing that early WRX used EJ205 with TD04 turbos while later WRX used EJ255 with TD04 variants informs parts compatibility.

Maintenance Planning

Engine-specific maintenance requirements vary by code. Timing belt intervals differ between engine families (60,000-105,000 miles depending on engine), valve adjustment requirements exist on some variants but not others (DOHC engines with hydraulic lash adjusters versus SOHC with mechanical clearances), and specific problem patterns (EJ25 head gaskets, EJ257 ringland failures) affect preventative maintenance priorities.

Conclusion: Decoding Subaru’s Engineering Language

Subaru’s engine designation system represents more than arbitrary alphanumeric codes—it’s a logical, information-dense language encoding essential engineering information into compact formats enabling immediate recognition of engine families, displacements, and configuration details critical for parts sourcing, maintenance, modification, and vehicle identification. The systematic approach to engine coding, refined across seven decades of production, demonstrates engineering discipline and organizational clarity that benefits everyone interacting with Subaru vehicles from factory technicians to independent mechanics to enthusiastic owners.

Understanding the evolution from early EK two-cylinder microcars through legendary EJ four-cylinder boxers to modern FB and FA platforms provides historical context illuminating Subaru’s engineering philosophy, market positioning, and the technological progressions enabling the company’s transformation from obscure Japanese manufacturer to globally recognized brand with fiercely loyal customer base. The boxer engine architecture maintained across virtually every Subaru for six decades represents commitment to distinctive engineering unusual among mainstream manufacturers, with engine codes serving as shorthand for this engineering heritage.

For Subaru owners and enthusiasts, engine code fluency enables confident navigation of parts catalogs, accurate communication with mechanics and suppliers, informed evaluation of potential vehicle purchases, and deeper appreciation of the engineering underlying these distinctive automobiles. Whether maintaining a high-mileage Legacy, modifying a WRX for track use, restoring a vintage Brat, or simply understanding what makes your Subaru tick, the ability to decode and interpret engine designations represents fundamental knowledge worth the modest effort required to master Subaru’s systematic, logical approach to engine identification.