The FA24 WRX: A New Era for Subaru Performance

Subaru’s introduction of the FA24 engine in the WRX marked a significant step forward for enthusiasts. The 2.4-liter turbocharged flat-four offers a robust foundation with factory internals capable of handling substantial power increases. While the stock engine produces around 271 horsepower, careful modification can push it well beyond 500 wheel horsepower. This guide focuses on the specific power mods and supporting components required to build a reliable 500 hp FA24 WRX, emphasizing real-world tuning practices and parts selection.

Understanding the FA24 Engine Architecture

The FA24 engine shares design DNA with the FA20 but features a larger displacement, revised cylinder heads, and improved cooling passages. Its closed-deck block (stronger than the earlier open-deck FA20) and forged connecting rods provide a solid starting point. However, reaching 500 hp demands careful management of boost, fuel, and heat. The direct injection system also needs consideration, as port injection may be required for higher fuel flow.

Factory Strengths and Weaknesses

The FA24’s cast-aluminum pistons are not forged, but they can tolerate moderate boost levels with proper tuning. The main weaknesses at high power are the fuel system and turbocharger. The stock twin-scroll turbo runs out of steam around 350-400 whp, and the high-pressure fuel pump struggles above 450 whp on ethanol blends. These are the primary bottlenecks addressed below.

Key Power Modifications for 500 HP

1. Upgraded Turbocharger and Boost Control

To reach 500 wheel horsepower, you must replace the stock turbo. A popular choice is a Garrett G25-660 or a BorgWarner EFR 6758, both offering quick spool and enough airflow for 500+ hp. For a street-friendly build, a twin-scroll setup with a 1.05 A/R turbine housing preserves low-end response. A high-performance wastegate (like a Tial MVR) and boost controller (e.g., an electronic solenoid from Cobb or GFB) are essential for consistent boost regulation.

Pro tip: Consider a turbo blanket and heat-wrap to reduce underhood temperatures and protect nearby components.

2. High-Performance Intercooler and Charge Pipes

Increased boost generates higher charge air temperatures. A large front-mount intercooler (FMIC), such as the Cobb or ETS unit, is almost mandatory for sustained power. The stock top-mount intercooler (TMIC) becomes heat-soaked quickly. Pair the FMIC with aluminum charge pipes (3-inch diameter recommended) to minimize flow restriction and pressure drop.

3. Fuel System Upgrades for High Horsepower

The FA24’s direct injection system can be supplemented with port injection to provide the fuel volume needed for 500 hp, especially on E85. A typical setup includes:

  • Upgraded high-pressure fuel pump (HPFP): Companies like Nostrum and HPA offer drop-in solutions that flow 20-25% more.
  • Larger fuel injectors: Direct injection injectors from Bosch (0280158825) can support 500 hp on ethanol.
  • Secondary port injection: A six-port injector plate (e.g., IAG or Crawford) with ID1050x injectors and a dedicated fuel rail ensures adequate fueling at high loads.

Don’t forget the low-pressure pump: a Walbro 525 or AEM 340 lph in-tank pump will keep the HPFP supplied.

4. Exhaust System for Flow

A free-flowing exhaust is critical. Replace the stock downpipe with a catless or high-flow catted unit (3-inch diameter). The mid-pipe and rear section should also be 3-inch mandrel-bent. Avoid excessive drone by choosing a resonated setup. A Borla or AWE Touring exhaust provides good flow without being overly loud.

5. Engine Management and Tuning

No 500 hp build succeeds without proper engine management. Options include:

  • ECU reflash: Cobb Accessport with a custom etune from a reputable tuner (e.g., Mike from X Tuning or Brentuning).
  • Standalone ECU: Motec M130 or Haltech Elite 1500 for full control, especially with port injection.

Critical parameters to tune: boost-by-gear, knock control, and flex-fuel readiness for E85. A good base calibration and professional dyno tuning are non-negotiable for reliability.

Supporting Components for Reliability and Control

1. Upgraded Clutch and Drivetrain

Stock clutch slips around 400 lb-ft. A South Bend Stage 3 daily or ACT HD clutch with a lightweight flywheel handles the torque. Upgrade the transmission mount and differential bushings to reduce driveline slop. For manual transmissions, a short-shifter kit (Boomba or Kartboy) improves shift feel. Consider upgrading the gearset if you plan frequent track use.

2. Suspension and Chassis Stiffening

Adding power without handling upgrades compromises safety and fun. Recommended mods:

  • Coilovers: KW V3 or Tein MonoSport allow adjustment of dampening and ride height.
  • Sway bars: Whiteline or Eibach with adjustable end links reduce body roll.
  • Strut tower braces and lower control arms: Aluminum arms reduce unsprung weight while improving geometry.

A good alignment (e.g., -2° front camber, -1.5° rear) transforms turn-in response.

3. Brake System Upgrades

Stopping a 500 hp WRX demands serious brakes. Upgrade front rotors to 2-piece directional units (like StopTech or Brembo) and pair with Carbotech XP10 pads. Stainless-steel braided lines reduce pedal sponginess. For track days, consider a brake duct kit to cool the calipers. Rear brake upgrades are less critical but matching pads and rotors ensure balance.

4. Cooling System Improvements

Heat management is the hidden killer of high-horsepower builds. The FA24 runs hot under boost. Essential upgrades:

  • Performance radiator: Koyo or Mishimoto aluminum radiators with increased core volume.
  • Oil cooler: A Setrab or Mocal thermostat-controlled oil cooler maintains oil temps below 230°F.
  • Transmission cooler: For CVT or automatic WRX models, an auxiliary cooler (Hayden or Derale) is mandatory.

A smart approach is to tackle supporting mods first, then add power mods step by step. A suggested order:

  1. ECU reflash, intercooler, downpipe, and catback exhaust (stage 2 gains ~330-350 whp).
  2. Clutch, brake pads, and cooling upgrades.
  3. Fuel system upgrades (HPFP + injectors) to run E85 reliably at 400-450 whp.
  4. Turbo upgrade and boost control, with dyno tune for 500-550 whp.

Important: Keep the stock intake if possible; many aftermarket intakes cause MAF scaling issues. Stick with a well-known tuner’s recommendation.

External Resources and Community Knowledge

Before buying parts, consult communities and proven builds. The Subaru XV Forums and IAG Performance offer trusted parts and install guides. For tuning, Cobb Tuning provides comprehensive software and hardware support. A valuable read on FA24 limitations is EngineLabs’ FA24 analysis.

Final Considerations for Long-Term Reliability

Building a 500 hp FA24 WRX is achievable, but longevity depends on maintenance and driving habits. Use a high-quality synthetic oil (5W-30 or 0W-40), change it every 3,000 miles, and check oil levels frequently. Install a wideband O2 sensor display to monitor air-fuel ratios. Avoid sustained full-throttle runs without proper cooling breaks. With careful parts selection and professional tuning, your FA24 WRX will deliver thrilling performance without premature failure.