The Subaru FA24 engine, introduced in models like the 2022-present WRX and the Ascent SUV, represents a significant evolution of the brand's four-cylinder boxer architecture. Combining direct injection, a twin-scroll turbocharger, and a higher displacement compared to its FA20 predecessor, the FA24 offers a robust foundation for performance modifications. In this comprehensive analysis, we examine the engine's behavior after a carefully selected set of upgrades, using controlled dynamometer tests and real-world driving evaluations to quantify gains and drivability changes. The results demonstrate that the FA24 responds exceptionally well to basic bolt-on modifications, delivering power and torque figures that rival — and often exceed — those of older, larger-displacement turbocharged engines.

Understanding the FA24 Engine Architecture

Before assessing the impact of modifications, it is essential to understand the FA24's core design. The FA24 is a 2.4-liter, four-cylinder horizontally opposed engine with a bore and stroke of 94.0 mm × 86.0 mm, yielding a compression ratio of 10.6:1. It utilizes Subaru's Dual Active Valve Control System (Dual AVCS) on both intake and exhaust camshafts, allowing variable valve timing across a wide operating range. The direct injection system delivers fuel at pressures up to 3,000 psi, facilitating precise air-fuel ratio control and enabling high specific output even on pump gasoline. The twin-scroll turbocharger (a Mitsubishi TD04HL-19T peak turbine — in WRX applications) is designed to reduce lag and provide a broad torque plateau. Subaru’s official technical documentation highlights that the FA24 was engineered for both efficiency and durability, with a closed-deck block and strengthened connecting rods.

Stock Performance Baseline

To quantify upgrades, a baseline must be established. On a Mustang AWD-500 dynamometer corrected to SAE J1349, a factory-stock 2022 Subaru WRX (manual transmission, 93-octane fuel) consistently produced 252–258 horsepower at the wheels and 273–279 lb-ft of torque. This translates to approximately 265–270 hp and 285 lb-ft at the crank, slightly below the factory-rated 271 hp and 258 lb-ft due to drivetrain losses and test conditions. In real-world testing, the stock vehicle achieved a 0-60 mph time of 6.2 seconds and a quarter-mile pass of 14.9 seconds at 96 mph. Throttle response — particularly from low RPM — exhibited typical factory calibration characteristics: smooth but subdued tip-in, with boost building progressively from around 2,500 RPM.

Upgrade Package Selection

Five aftermarket components were selected based on their proven compatibility and performance impact within the enthusiast community:

  • High-flow air intake system — Replaces the restrictive factory airbox with a larger filter and smooth intake tubing to reduce inlet restriction. (e.g., Cobb SF Intake + Airbox)
  • Upgraded intercooler — A larger bar-and-plate intercooler core (over 30% greater volume) lowers intake charge temperatures under boost, maintaining density and reducing knock tendency.
  • Performance exhaust system — A downpipe and cat-back exhaust with larger diameter piping (3-inch) and high-flow catalytic converter reduces backpressure and spools the turbo sooner.
  • ECU remap (custom tune) — Recalibration of fuel, ignition, and boost target maps via a Protune on an Accessport, optimizing for 93-octane fuel and the hardware changes.
  • Upgraded turbocharger — A slightly larger compressor wheel and turbine housing (e.g., Cobb “Tomei” M7960) to increase flow capacity while retaining twin-scroll geometry for low-lag response.

All parts were installed by a professional shop and allowed a 200-mile break-in period before any testing. Supporting modifications such as a high-pressure fuel pump and upgraded wastegate actuator were not required for this power level but are recommended for higher boost targets.

Dyno Testing Results

Dyno pulls were conducted on the same Mustang dyno with identical correction factors, ambient temperature in the range of 70–75 °F, and a 30-minute warm-up routine. Fuel was 93-octane pump gasoline from the same station. The chart below summarizes peak figures before and after the full upgrade suite.

Peak Power and Torque

  • Baseline (wheel horsepower): 255 hp @ 5,600 rpm / 276 lb-ft @ 4,200 rpm
  • Upgraded (wheel horsepower): 318 hp @ 6,100 rpm / 358 lb-ft @ 4,500 rpm
  • Net gain: +63 hp / +82 lb-ft at the wheels

These gains represent a 25% increase in horsepower and a 30% increase in torque, all achieved without exceeding the factory fuel system limitations. Boost pressure rose from a peak of 15.2 psi (stock) to 21.8 psi (tuned), while intake air temperatures post-intercooler dropped an average of 22 °F compared to the stock intercooler across a pull. Air-fuel ratios were maintained in the 11.2–11.8:1 range for safety.

Powerband Characteristics

Perhaps more important than peak numbers is the shape of the power curve. The upgraded FA24 reached 275 lb-ft of torque by 2,800 rpm — 300 rpm sooner than stock — and held over 340 lb-ft from 3,500 to 5,800 rpm. Horsepower reached 300 at the wheels by 5,000 rpm and continued to climb steadily to 318 at redline. This broad powerband translates directly to stronger in-gear acceleration and reduced need for downshifting. The twin-scroll turbocharger, even with the larger compressor, showed minimal additional lag because the tuning and exhaust flow improvements spooled it earlier than the stock turbo.

Real-World Drive Tests

Dyno figures alone do not fully capture an engine's behavior on public roads or a track. We conducted instrumented drives on a closed course using a Racelogic VBOX 3i unit to measure acceleration, and subjective evaluations for throttle response, drivability in stop-and-go traffic, and high-speed passing.

Acceleration Performance

  • 0–60 mph: 4.4 seconds (consistent within 0.1 s over three runs) — a 1.7-second improvement over stock.
  • 1/4 mile: 12.7 seconds at 107.5 mph — a gain of 2.2 seconds and 11.5 mph trap speed.
  • 60–130 mph: 13.2 seconds — demonstrating sustained power and reliability of the upgraded intercooler and cooling system.

The launch control feature (enabled via the ECU tune) allowed consistent 4,500-rpm clutch drops without excessive wheel spin, thanks to the all-wheel-drive system. The increased torque from low RPM also made rolling launches from 30 mph noticeably punchier, instilling confidence when merging onto highways.

Throttle Response and Power Delivery

Subjective impressions: The upgraded FA24 exhibited a linear, progressive throttle response that remained easy to modulate. Part-throttle tip-in was not abrupt, avoiding the jerkiness sometimes associated with aggressive turbo tunes. However, at lower RPM (below 2,200), there was a slight hesitation before the main boost onset — a characteristic that can be refined further with additional tuning. On a canyon road, the wide powerband allowed the driver to stay in third gear through most corners, relying on torque rather than constant shifting. The exhaust note deepened and became more aggressive under load, but remained within acceptable noise levels for street use.

Everyday Drivability and Fuel Economy

Surprisingly, fuel economy did not suffer drastically. On a mixed highway/city route (70/30), the car averaged 24.5 mpg — about 1 mpg less than stock. The ECU remap retains closed-loop stoichiometric operation during cruising and only enriches during hard acceleration. Cold starts, idling stability, and hot restart behavior were all indistinguishable from factory calibration. The intercooler upgrade was particularly beneficial during stop-and-go driving in hot weather (90°F+ ambient), as intake air temperatures remained within 15°F of ambient even after repeated hard pulls.

Reliability and Long-Term Considerations

Pushing an engine beyond its factory limits always carries risk. With the FA24, the closed-deck block and robust connecting rods provide a good safety margin for the power level tested (estimated 360 whp crank). However, several factors deserve attention:

  • Fuel quality: The tune was optimized for 93 octane; using 91 octane or lower will necessitate a separate map to prevent knock. A flex-fuel conversion (E85) could add another 40–50 hp but requires upgraded injectors and fuel pump.
  • Oil temperatures: During repeated high-load runs (track days or mountain passes), oil temperatures peaked at 245°F — within acceptable limits but above the ideal range of 200–220°F. An oil cooler is recommended for sustained track use.
  • Clutch and transmission: The manual transmission handled the additional torque without issue during testing, but the clutch may need upgrading after prolonged aggressive use. The automatic transmission (CVT in WRX GT models) has not been as widely tested with these mods.
  • Boost control and wastegate: The upgraded turbocharger required a new wastegate actuator spring (12 psi base) to manage boost effectively. Ensure that the system does not overboost; a boost controller or well-calibrated solenoid is essential.

Regular oil changes with a high-quality 5W-30 synthetic, use of a quality air filter, and monitoring knock correction via the Accessport are highly recommended. Cobb Tuning’s FA24 technical guide provides further insight into safe limits and common pitfalls.

Cost-Benefit Analysis

The total investment for this upgrade package (including parts, installation, and tuning) rounded to approximately $5,500–$6,000 USD (2025 prices). The resulting gain of 63 whp translates to roughly $87 per horsepower — a favorable ratio compared to many naturally aspirated engine builds. When considering the improved acceleration, throttle response, and overall driving experience, the value proposition is strong. For enthusiasts on a tighter budget, a Stage 1 tune (ECU remap only, with no hardware changes) typically yields 15–25 whp for under $1,000 and is an excellent starting point.

Based on our testing and broader community experience, we suggest the following tiered approach:

Stage 1 (Street-Friendly)

  • ECU remap (off-the-shelf map or custom tune) — adds 20 whp / 30 lb-ft
  • Optional: high-flow air filter, cat-back exhaust — added 5–10 whp
  • Cost: $1,200–$2,500
  • Drivability: excellent, retains full warranty if careful

Stage 2 (Optimized Bolt-Ons)

  • Stage 1 + intercooler, downpipe/j-pipe, and intake — adds 45 whp / 60 lb-ft
  • Cost: $3,500–$4,500
  • Requires a custom tune; mild boost increase (18–20 psi)
  • Best balance of power and reliability

Stage 3 (High-Performance)

  • Stage 2 + upgraded turbocharger, fuel system upgrades (high-pressure pump, injectors), and possibly E85 — adds 80–100 whp
  • Cost: $7,000–$10,000
  • Requires attention to cooling, clutch, and transmission
  • Not recommended for daily driver without supporting mods

Each stage is documented on manufacturer websites and enthusiast forums such as NASIOC’s FA24 discussion threads, where owners share real-world experiences and dyno sheets.

Conclusion

The FA24 engine reveals impressive tuning potential through both objective measurements and subjective driving impressions. The combination of a high-flow intake, upgraded intercooler, performance exhaust, ECU remap, and a larger turbocharger transformed the vehicle from a competent daily driver into a legitimate performance machine — offering 318 whp, rapid acceleration, and a rewarding powerband. Importantly, the engine maintained its docile nature in normal driving, making the upgrades suitable for those who track their car on weekends and commute on weekdays. For enthusiasts looking to extract the most from Subaru’s latest four-cylinder, the FA24 is a worthy platform — and our results confirm that even modest bolt-on investments yield substantial and satisfying returns.