Subaru’s boxer engines have powered some of the most beloved all-wheel-drive vehicles on the road. Two engines stand out in Subaru’s modern lineup: the EJ25 and FA24. Both deliver that distinctive boxer rumble, but they represent different eras of engineering with unique strengths and weaknesses.
EJ25 Engine Overview: The Veteran Boxer
The EJ25 served as Subaru’s workhorse from 1995 through 2019 in various forms. You’ll find this 2.5-liter naturally aspirated boxer in countless Outbacks, Foresters, and Legacy models. The engine underwent several revisions over its long production run, with the most significant updates coming in 2011 when Subaru introduced the FB25 variant.
Power output varies depending on the specific year and application. Most EJ25 engines produce between 165-175 horsepower and 166-174 lb-ft of torque. The engine uses traditional port fuel injection and features Subaru’s Active Valve Control System (AVCS) on intake camshafts in later versions.
You’ll recognize the EJ25’s characteristic boxer rumble immediately. The horizontally opposed layout keeps the center of gravity low, contributing to Subaru’s reputation for balanced handling. The engine bay packaging also allows for excellent all-wheel-drive integration.
FA24 Engine Overview: The Modern Evolution
Subaru introduced the FA24 in 2019 as part of their next-generation engine family. This 2.4-liter naturally aspirated boxer represents a complete redesign rather than an evolution of the EJ platform. You’ll find the FA24 in newer Outbacks, Ascents, and Legacy models, plus a turbocharged version powers the latest WRX.
The FA24 produces significantly more power than its predecessor. The naturally aspirated version delivers 182-184 horsepower and 176-177 lb-ft of torque, depending on the application. The turbocharged FA24 in the WRX pushes out 271 horsepower and 258 lb-ft of torque.
Modern technology defines the FA24 experience. Direct injection, dual active valve control systems, and improved combustion chamber design all contribute to better efficiency and performance. The engine also meets stricter emissions standards while delivering more power.
Performance Comparison: Power and Efficiency
The FA24 wins the power battle decisively. Even the naturally aspirated version offers 10-15 more horsepower than the EJ25, with better torque delivery across the rev range. You’ll notice the difference during highway merging and uphill climbs, especially in heavier vehicles like the Outback.
Fuel economy improvements with the FA24 are substantial. Most FA24-powered vehicles achieve 2-4 mpg better combined fuel economy compared to their EJ25 predecessors. The direct injection system and improved thermal efficiency make a real difference at the pump.
Throttle response feels sharper with the FA24, particularly in naturally aspirated form. The engine revs more freely and feels more eager throughout its power band. The EJ25 has a more leisurely character that some drivers prefer for relaxed driving.
The EJ25 Head Gasket Problem
Head gasket failures became synonymous with the EJ25, particularly in models from 1999-2009. The original composite head gaskets couldn’t handle the thermal cycling of the boxer layout. External coolant leaks were the most common symptom, often appearing around 100,000-150,000 miles.
Subaru revised the head gasket design multiple times, with significant improvements starting in 2010. The updated multi-layer steel (MLS) gaskets proved much more durable. However, the reputation damage was already done, and many potential buyers still avoid EJ25-powered vehicles.
When head gaskets fail, you’re looking at $1,500-2,500 for professional replacement. The job requires removing both cylinder heads and typically includes timing belt service. Many owners proactively replace head gaskets during timing belt maintenance to avoid roadside failures.
FA24 Direct Injection Carbon Buildup
Direct injection brings efficiency gains but creates new maintenance challenges. The FA24’s direct injection system sprays fuel directly into combustion chambers, bypassing intake valves entirely. This means no fuel washes over intake valves to clean away carbon deposits.
Carbon buildup on intake valves becomes inevitable with direct injection engines. The deposits reduce airflow and can cause rough idle, misfires, and reduced power. Most FA24 engines will need intake valve cleaning every 60,000-80,000 miles, costing $300-600 depending on your location.
Catch can installations help reduce carbon buildup by preventing oil vapors from entering the intake system. Several aftermarket companies offer bolt-on catch can kits for FA24-powered vehicles. Regular oil changes with high-quality oil also slow carbon accumulation.
Reliability and Maintenance Costs
The FA24 shows promising early reliability, but its relative newness means long-term durability remains unknown. Initial reports suggest fewer oil consumption issues compared to early EJ25 engines. The improved piston ring design and better cylinder bore coatings appear effective.
Routine maintenance costs favor the EJ25 slightly. Oil changes, spark plugs, and basic services cost about the same, but the EJ25’s timing belt is cheaper to replace than the FA24’s timing chain when problems arise. However, timing chains typically last much longer than belts.
Parts availability strongly favors the EJ25 due to its long production run. Aftermarket support is extensive, with numerous companies offering performance and replacement parts. FA24 aftermarket support is growing but still limited compared to the mature EJ25 ecosystem.
Applications Across Subaru’s Lineup
The EJ25 powered multiple generations of popular Subaru models. You’ll find it in 2000-2019 Outbacks, 1998-2018 Foresters, and 2005-2019 Legacy models. The WRX used a turbocharged EJ25 from 2006-2014, creating a strong enthusiast following.
FA24 applications are expanding rapidly as Subaru transitions their lineup. The 2020+ Outback and Legacy use naturally aspirated FA24 engines, while the Ascent three-row SUV features a turbocharged version. The 2022+ WRX marks the return of FA24 power to Subaru’s performance flagship.
Each application tunes the engines differently for specific vehicle characteristics. The Outback prioritizes low-end torque for towing and off-road capability, while the WRX version emphasizes peak power and aggressive throttle response.
Tuning and Modification Potential
The EJ25 enjoys massive aftermarket support, especially turbocharged versions. Decades of development created proven upgrade paths for every power level. Simple bolt-on modifications can add 50+ horsepower to turbocharged EJ25 engines with supporting modifications.
Naturally aspirated EJ25 tuning options are more limited but still available. Cold air intakes, exhaust systems, and ECU tuning can add 10-20 horsepower. The real gains come from forced induction conversions, though these require significant investment.
FA24 tuning is still developing but shows promise. The direct injection system responds well to tuning, and the stronger internals handle moderate power increases safely. Turbocharged FA24 engines in the WRX already see substantial gains from simple modifications.
Which Engine Should You Choose?
Your priorities determine the better choice between these engines. The FA24 offers superior performance, efficiency, and modern technology. If you want the latest features and best fuel economy, FA24-powered vehicles are the clear choice.
The EJ25 makes sense for budget-conscious buyers or those who prefer proven technology. Used vehicles with well-maintained EJ25 engines can provide excellent value, especially if head gasket issues were already addressed. Parts availability and repair expertise are also more widespread.
Consider your maintenance preferences carefully. The EJ25’s head gasket vulnerability requires proactive maintenance but is well-understood by most mechanics. The FA24’s carbon cleaning needs are newer territory for many service shops.
Long-Term Ownership Considerations
Resale value trends favor FA24-powered vehicles currently. Buyers perceive newer technology as more desirable, and improved fuel economy adds appeal. However, this could shift as FA24 engines age and develop their own reputation.
Insurance costs typically don’t vary significantly between engines in the same vehicle. The WRX represents an exception, where turbocharged versions of both engines carry higher premiums than naturally aspirated alternatives.
Warranty coverage strongly favors newer FA24 vehicles. Most EJ25-powered vehicles are out of factory warranty, while FA24 engines still enjoy full coverage. Extended warranty options are more readily available for newer vehicles.
Frequently Asked Questions
Are FA24 engines more reliable than EJ25 engines?
Early data suggests FA24 engines avoid the head gasket issues that plagued early EJ25 engines. However, the FA24’s direct injection system requires regular intake valve cleaning that the EJ25 doesn’t need. Both engines can be reliable with proper maintenance, but they have different service requirements.
Can I retrofit an FA24 engine into an older Subaru?
Engine swaps between EJ25 and FA24 are extremely complex due to different engine management systems, wiring harnesses, and mounting points. The FA24 requires extensive modifications that make such swaps impractical for most owners. Stick with factory applications for both engines.
Which engine is better for towing?
The FA24’s additional torque and more sophisticated engine management make it superior for towing. The extra 10-15 lb-ft of torque helps when pulling trailers, and the improved thermal management handles sustained loads better. Most FA24-powered vehicles also have higher tow ratings than their EJ25 predecessors.
Do both engines require premium fuel?
Naturally aspirated versions of both engines run fine on regular 87-octane fuel. Turbocharged variants of both engines require premium 91+ octane fuel for optimal performance and reliability. Using regular fuel in turbocharged engines can cause knock and potential engine damage.
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