Does Subaru STI have a Boxer engine?
Yes. Subaru’s STI models use horizontally opposed “boxer” engines, a hallmark of the brand’s performance lineup.
Subaru Tecnica International (STI) is the performance division of Subaru, and its cars have long relied on flat-four, turbocharged powerplants. This article explains how the boxer engine layout underpins STI performance, how the engine technology has evolved across generations, and where the STI badge stands today.
Boxer engines: Subaru’s performance foundation
Boxer engines are characterized by cylinders arranged in opposed pairs that move in and out together, like a boxer’s fists. This layout lowers the engine’s center of gravity, reduces vibration, and helps with balance—benefits that translate to sharper handling and a connected driving feel in performance cars such as STI models.
For STI cars, the boxer configuration is complemented by turbocharging and all-wheel drive, reinforcing Subaru’s focus on grip, stability, and cornering ability.
- Lower center of gravity enhances handling and steering response in tight corners.
- Opposed-piston balance minimizes vibrations, improving ride quality at high RPMs.
- Compact, flat layout supports Subaru’s symmetrical AWD architecture and drivetrain packaging.
In short, the boxer engine is a core element of STI’s performance philosophy and contributes to the brand’s distinctive driving dynamics.
STI engines through the years
Below is a concise look at how STI powerplants have evolved while preserving the boxer layout.
- Early STI generations used turbocharged flat-four engines from Subaru’s EJ-series family, with displacement and tuning optimized for performance and all-wheel drive.
- As technology progressed, Subaru transitioned to newer flat-four engine families (FA/FB) that retain the boxer configuration but incorporate modern features such as improved turbocharging, direct injection, and emissions refinements.
- In recent years, Subaru’s performance models continued to rely on turbocharged boxer fours; the standard WRX lineup introduced a 2.4-liter turbo flat-four in the latest generation, while the STI badge has not seen a mass-market revival as of 2025.
These points illustrate how the STI name has remained tied to the boxer engine philosophy even as the exact engine family and displacement have evolved over time.
Current status and future prospects
As of 2025, Subaru has not released a new WRX STI, and the performance badge sits outside active mass-market production. The contemporary WRX continues to use a turbocharged boxer engine (in recent years a 2.4-liter flat-four), keeping Subaru’s signature engine layout intact in its core lineup. Subaru has not officially announced a concrete plan to reintroduce a full-fledged STI model, though the boxer engine platform remains a central and enduring element of the brand’s performance engineering.
Advocates of the STI legacy argue that the fundamental advantages of the boxer layout—low center of gravity, balanced handling, and strong AWD integration—will continue to influence Subaru’s high-performance offerings, even if a dedicated STI badge is temporarily on pause.
Summary
The STI line is built on Subaru’s boxer engine tradition—a horizontally opposed, turbocharged four-cylinder arrangement that provides a low center of gravity and refined balance for performance driving. Over the years, STI engines evolved from the EJ-series to newer FA/FB boxer designs, all while preserving the distinctive flat-four configuration. As of now, there is no active mass-market STI model in production, though Subaru maintains its commitment to the boxer engine across its performance lineup and future developments.
What kind of engine is in a Subaru STI?
The Subaru STI engine is a high-performance, turbocharged, boxer-four engine developed by Subaru Tecnica International for performance models like the WRX STI. Historically, the engine was a 2.5-liter EJ25, producing around 300 horsepower, but newer models were expected to feature a 2.4-liter FA24F engine. The STI engine is known for its power, manual transmission, and, most notably, its symmetrical all-wheel-drive system.
Key characteristics
- Boxer engine: The STI engine is a flat-four, turbocharged boxer engine, which means its cylinders are horizontally opposed and located in a flat configuration. This design lowers the car's center of gravity for better handling.
- Performance tuning: Subaru Tecnica International (STI) creates these engines by fine-tuning existing Subaru engines to a higher level of performance.
- Historical performance: The previous generation of the WRX STI featured a 2.5-liter turbocharged engine with around 300 horsepower and 290 lb-ft of torque, according to Perth City Subaru and Subaru Oman.
- All-wheel drive: The STI is equipped with a symmetrical all-wheel drive system, which is a hallmark of the performance package. This system is often paired with a driver-controlled center differential (DCCD) for performance adjustments.
- Legacy and future: While the WRX STI production concluded after its first generation, the STI performance badge is still used in other Subaru performance vehicles and concepts, such as the upcoming 2026 Performance-B STI Concept.
Does the STI have a boxer engine?
While both are turbocharged SUBARU BOXER® engines, the WRX STI's powerplant is built for maximum power and a more aggressive output.
What year STI to stay away from?
The Subaru years to avoid are 2008-2014, particularly the 2008-2010 models, due to engine problems like ringland failures and weak transmissions. Another year to be cautious of is the 2015 model, which had a recall lawsuit regarding rod bearings. Early 2017 models had issues with the pitch stop brace, so later models from 2017 onwards are generally better.
Years to avoid
- 2008-2014: This generation is frequently cited as one with significant issues.
- The 2008 model year is often singled out as the worst due to its redesign, engine problems (including ringland failures), and a weak 5-speed transmission.
- The entire generation from 2008-2014 experienced engine issues and had an unappealing redesign.
- 2015: This model year is known for having a rod bearing recall lawsuit.
- Early 2017: Models from the beginning of the 2017 model year had a problem with the pitch stop brace welds cracking, though this was fixed in later 2017 models and onwards.
Why these years are problematic
- 2008-2014: This generation was a new chassis with engine and transmission problems. The 5-speed transmissions in earlier models were particularly weak.
- 2015: The rod bearing recall is a major issue that can lead to engine failure.
- Early 2017: The cracked pitch stop brace issue is a safety concern that needs to be addressed.
What to look for instead
- Later model years like 2018-2021 are generally considered more reliable as Subaru fixed many of the small issues from previous generations.
- For later models (2017 onwards), ensure the pitch stop brace has been addressed if you are looking at an early 2017 model.
Which Subaru has a boxer engine?
All current Subaru models have Boxer engines, including the Ascent, BRZ, Crosstrek, Forester, Impreza, Legacy, Outback, and WRX. Subaru is known for being one of the few manufacturers to use this horizontally opposed piston engine design across its entire lineup.
- Ascent: Features a 2.4L turbocharged Boxer engine.
- BRZ: Equipped with a 2.0L Boxer engine.
- Crosstrek: Comes with a 2.0L Boxer engine in base models, with higher trims offering a 2.5L Boxer engine or a hybrid powertrain.
- Forester: Comes with a standard 2.5L Boxer engine.
- Impreza: Comes with a standard 2.0L Boxer engine.
- Legacy: Comes with a standard 2.5L Boxer engine, with an available 2.4L turbocharged Boxer engine.
- Outback: Comes with a standard 2.5L Boxer engine, with an available 2.4L turbocharged Boxer engine.
- WRX: Features a 2.0L turbocharged Boxer engine, while the WRX STI uses a 2.5L turbocharged Boxer engine.
