When choosing a powerplant for a Subaru build, the debate between the FA24 and the EJ series engines often comes down to a single question: which offers the best balance of power and cost? The FA24 represents the latest in boxer-engine technology, while the EJ series has built a legendary reputation over decades of rally dominance and street performance. Understanding the nuances of each platform—not just peak numbers, but real-world drivability, reliability, and long-term ownership costs—is essential before making a purchase. This comparison breaks down the FA24 and EJ series engines across performance, efficiency, budget, and modification potential, helping you decide which engine aligns with your goals.

Deep Dive: The FA24 Engine

Design and Architecture

The FA24 is a 2.4-liter turbocharged flat-four (boxer) engine that debuted in the 2020 Subaru Legacy XT and Outback XT, before finding its way into the 2022+ Subaru WRX and the 2023+ Subaru BRZ (in naturally aspirated form). Its design builds upon lessons learned from the FA20, focusing on increased displacement and improved thermal efficiency. Key features include a semi-closed deck block, direct injection (D4S), a twin-scroll turbocharger (on turbo applications), and an integrated exhaust manifold within the cylinder head. These choices reduce turbo lag, improve throttle response, and allow for higher boost pressures from the factory.

  • Displacement: 2,387 cc (2.4 L)
  • Configuration: Flat-four, DOHC, 16-valve
  • Compression Ratio: 10.6:1 (turbo), 12.5:1 (NA)
  • Fuel System: Direct injection plus port injection (D4S)
  • Turbocharger: Twin-scroll (WRX, Legacy/Outback XT)
  • Factory Power Output: 271 hp (WRX) / 260 hp (Legacy/Outback)
  • Factory Torque: 258 lb-ft (WRX) / 277 lb-ft (Legacy/Outback)

Strengths of the FA24

The FA24’s modern architecture delivers immediate torque from low RPMs, thanks to the twin-scroll turbo and direct injection. The D4S system also helps mitigate carbon buildup on intake valves—a common issue with direct-injection-only engines. The semi-closed deck design provides a strong foundation for moderate boost increases without needing an immediate block upgrade. For daily drivers who want responsive power and decent fuel economy, the FA24 is a compelling package.

Limitations

While the FA24 is robust for a production engine, its aftermarket is still maturing compared to the EJ series. Aftermarket pistons, rods, and camshaft options are less plentiful in 2025, and the direct injection system adds complexity for those wanting to run high-ethanol blends without port injection upgrades. Additionally, the FA24’s exhaust manifold integrated into the head limits some aftermarket header designs, which can be a consideration for those chasing every last horsepower.

Deep Dive: The EJ Series Engine

Design and Evolution

The EJ series has been Subaru’s performance workhorse since the early 1990s. It encompasses a wide range of displacements and configurations, but the most performance-oriented variants are the EJ20 (2.0L) and EJ25 (2.5L) turbocharged engines found in the Impreza WRX STI and Legacy GT. The EJ25, especially the EJ257 found in USDM STIs from 2004 to 2021, is the benchmark for Subaru performance. It features a closed-deck block (late-model EJ257), semi-closed deck (earlier versions), and port injection only.

  • Displacement: 1,994 cc (EJ20) / 2,457 cc (EJ25)
  • Configuration: Flat-four, DOHC, 16-valve
  • Compression Ratio: 8.2:1 (EJ257) to 9.0:1 (EJ207)
  • Fuel System: Port injection
  • Turbocharger: VF series or twin-scroll (depending on variant)
  • Factory Power (EJ257): 305 hp (2004-2007), 300 hp (2008-2021)
  • Factory Torque (EJ257): 290-300 lb-ft

Strengths of the EJ Series

The EJ series boasts a massive aftermarket ecosystem. Whether you need forged internals, custom intake manifolds, or standalone ECU support, there are decades of proven parts and tuning knowledge available. The port injection system simplifies high-ethanol fuel setups and allows for easy fuel system upgrades. The closed-deck blocks in later STIs are legendary for handling 450+ whp with only rods and pistons. For a dedicated performance build, the EJ often wins on sheer availability of upgrade paths.

Limitations

EJ engines are older technology. They are known for oiling issues (particularly with the banjo bolt screen in early models), ringland failures on high-mileage stock tunes, and blow-by at higher boost levels. Fuel economy is worse than the FA24 due to older injection and tuning strategies. Furthermore, the stock turbochargers on USDM EJ25s are undersized compared to the FA24’s twin-scroll unit, resulting in a more peaky powerband that falls off up top.

Performance Comparison: FA24 vs. EJ Series

Horsepower and Torque Curves

On paper, the FA24 and EJ25 produce similar peak horsepower numbers, but the driving experience is markedly different. The FA24’s twin-scroll turbo spools significantly earlier, often reaching peak torque around 2,000-2,500 RPM, whereas a stock EJ25 typically peaks near 4,000 RPM. This gives the FA24 a flatter, more linear torque curve that feels faster in daily driving and on the street. The EJ25, by contrast, offers a more dramatic surge at mid-range but falls off after 5,500 RPM due to its smaller turbo and restrictive exhaust manifold. For reference, the FA24 in the 2022+ WRX puts down about 240-250 whp stock, while a stock EJ257 typically dynos between 230-250 whp depending on the year. So peak numbers are close, but the FA24 delivers its power lower in the rev range.

Acceleration and Responsiveness

In a drag race or street pull, the FA24’s earlier torque gives it an advantage from a standstill and during roll-ons. However, the EJ25’s higher peak torque can feel more aggressive when it comes on boost. In terms of throttle response, the FA24’s direct injection and shorter intake runner length provide crisper tip-in, while older EJ engines can feel vague off-idle due to port injection and larger plenum volumes. On a track, the EJ’s peaky nature can be managed with gear selection, but the FA24’s linear power often makes it easier to drive fast consistently.

Aftermarket and Modification Potential

This is where the EJ series still holds a notable edge—though the gap is closing. With decades of development, you can buy forged pistons, rods, upgraded oil pumps, billet crank supports, and oversized valves for any EJ variant. A built EJ257 can handle 700+ hp with proper tuning. The FA24 aftermarket, while growing rapidly, is roughly where the EJ was in 2008. That said, the FA24’s stronger factory block (semi-closed deck vs. the EJ’s semi-closed or open deck in some years) means it can hold 400 whp on stock internals with a conservative tune. Companies like IAG, Cobb, and Killer B are now producing FA24 components, but parts availability and shop familiarity still favor the EJ in many regions.

Key Aftermarket Support Comparison
Component FA24 Availability EJ Availability
Forged Pistons Good (CP, JE, Manley) Excellent
Forged Connecting Rods Good Excellent
Drop-in Pistons & Rods Limited Excellent
Variable Valve Timing (AVCS) Tuning Adequate Excellent
Standalone ECUs Good (Link, Motec, Haltech support) Excellent

Fuel Efficiency

Modern emissions and efficiency standards heavily influenced the FA24’s design. With direct injection, a higher compression ratio, and improved thermal management, the FA24 typically achieves 24-26 mpg combined in turbocharged applications. The EJ25 in the STI, by contrast, is notorious for poor fuel economy, often returning 18-21 mpg combined in real-world driving. The FA24’s efficiency advantage is not trivial—over 100,000 miles, it can save you roughly $1,500 in fuel costs at current premium gas prices. For daily drivers on a budget, this makes the FA24 a clear winner.

Cost Considerations: Which Engine Fits Your Budget?

Initial Purchase Price

New vehicles with the FA24 (e.g., 2022+ WRX) typically start around $31,000, while the last EJ-powered STI (2021 model) had a base MSRP around $37,000. However, used market prices complicate the equation. A 2021 STI with 30,000 miles might still command $38,000+ due to its cult status, whereas a 2024 WRX with similar mileage can be found for $30,000. If you are buying a new or nearly new car, the FA24 gives you a lower entry price and comparable performance.

Maintenance and Reliability

Long-term maintenance costs depend on how you treat the engine. Both engines require strict adherence to oil change intervals (3,000-5,000 miles recommended with synthetic oil). The FA24’s direct injection can lead to carbon buildup on the intake valves over time—normally around 60,000-80,000 miles—requiring a walnut blasting service costing $400-$600. The EJ series, with only port injection, avoids that expense but may need timing belt replacements every 105,000 miles (FA24 uses a timing chain). The EJ also has a known weakness with its coolant crossover pipe cracking in older models. On average, the FA24 may have slightly lower annual maintenance costs for a daily driver, but the difference is marginal.

Modification Budget

If you plan to modify, the EJ’s mature aftermarket means you can often find used parts (e.g., a used Cobb Accessport, turbos, intercoolers) for much less than new FA24 components. A basic Stage 2 build on an EJ257 (aftermarket downpipe, tune, intake) can cost $1,500-$2,500 and yield 300-320 whp. A comparable FA24 build might cost $2,000-$3,000 due to newer parts and less used market saturation. For high-horsepower builds (500+ hp), the EJ still offers more proven and affordable paths because you can buy complete pre-built longblocks from IAG or Outfront for $6,000-$10,000. FA24 built blocks are starting to appear but are fewer and often more expensive.

Which Engine Should You Choose?

For the Daily Driver on a Budget

The FA24 is the clear choice. Its lower initial vehicle cost, better fuel economy, and flatter torque curve make it far more livable every day. You also get modern amenities like a quieter cabin, better stereo, and updated safety systems in the 2022+ WRX compared to the aging EJ-based STI. The FA24’s reliability and simpler maintenance (timing chain, no banjo bolt issues) also favor long-term ownership peace of mind.

For the Dedicated Track or High-Horsepower Build

The EJ series still makes sense if you are aiming for 600+ hp or building a full track car. The aftermarket is unmatched, and the wealth of tuning knowledge means any shop experienced with Subarus can help. The port injection system simplifies fuel supply, and the closed-deck blocks available in later STIs provide a bulletproof foundation. If you don’t mind the older chassis and worse fuel economy, the EJ257 remains the gold standard for extreme Subaru builds.

For the Enthusiast Who Wants Both

Some owners have started swapping FA24s into older EJ chassis (like the 2004-2007 STI) using custom wiring harnesses and tuning. This is an expensive but rewarding path that gives you the FA24’s modern torque and efficiency in a lighter, more iconic chassis. If you have a high budget ($10,000-$15,000 for a full swap) and enjoy a challenge, that hybrid approach offers the best of both worlds.

External Resources for Further Research

  • Subaru WRX Official Site – Factory specs and pricing for FA24-equipped WRX.
  • IAG Performance – Aftermarket engine components and built blocks for both FA and EJ engines.
  • Tuning Tech FS – Data logging and dyno results comparing FA24 and EJ performance curves.
  • NASIOC Forums – Community build threads and reliability reports for both platforms.
  • Cobb Tuning – Accessport and stage kits for FA24 and EJ engines.

Final Verdict

Choosing between the FA24 and EJ series engines ultimately hinges on your priorities. If you want a modern, efficient, and responsive daily driver with enough power to have fun, the FA24 wins on nearly every metric—especially when factoring in budget. If your heart is set on building a 500+ horsepower street monster or you already own an EJ-based chassis with a proven aftermarket, the EJ series remains a valid, time-tested option. Understand that the FA24 is the present and future of Subaru performance, while the EJ represents a legendary past that still has plenty of life left for dedicated builders. Let your driving needs and budget decide.