Understanding the FA24 Engine

The FA24 engine, a 2.4-liter turbocharged flat-four, debuted as the heart of Subaru’s second-generation BRZ and Toyota GR86, and later found use in other applications such as the Subaru Ascent and Outback XT. Unlike the earlier FA20, the FA24 features a larger displacement, a beefier cylinder block, and a twin-scroll turbocharger from the factory. This design delivers excellent low-end torque and a broad powerband, producing 270 hp and 258 lb-ft of torque in stock form on the BRZ/GR86. The engine employs direct injection only (D-4S dual injection was dropped), which simplifies the fuel system but places extra demand on fuel pump and injector capacity when chasing higher horsepower.

The FA24’s closed-deck block design and forged connecting rods provide a robust foundation for increased boost. However, the stock turbocharger, a TD04L twin-scroll unit, reaches its efficiency limit around 18–20 psi, making it a prime candidate for replacement. The engine management system is fully encrypted and requires external tuning solutions (e.g., ECUtek, Cobb Accessport) to rewrite fuel and ignition maps. Understanding these fundamentals is key before planning a $2,500 upgrade path to exceed 330 horsepower.

Turbocharger Upgrade Options

Selecting the right turbocharger for the FA24 depends on your desired power level, spool characteristics, and budget. For a 330+ hp build, three standouts dominate the market:

Garrett GTX2860R Gen II

This ball-bearing turbocharger offers incredibly quick spool, reaching full boost by 3,000 rpm. Its 52mm compressor wheel flows enough air for 360–380 whp on pump gas with proper supporting modifications. The GTX2860R Gen II is a favorite for those wanting to maintain near-stock drivability while adding a substantial power gain. It uses a T25 flange (compatible with aftermarket FA24 headers) and requires a custom oil feed line.

Blouch 20G XT-R

Blouch’s 20G XT-R hybrid turbocharger is built on a stock TD04L frame but upgrades to a billet compressor wheel and extended-tip technology. It’s a direct bolt-on replacement using the factory water and oil lines – ideal for DIY installers. The 20G XT-R supports up to 400 hp and spools only slightly later than the stock unit (full boost by 3,200 rpm). It’s a reliable middle-ground option that pairs well with stock intercooler locations.

Forced Performance FP Green (FA24-specific)

For those targeting 400+ hp, the FP Green offers a 61mm compressor wheel and a ported shroud housing. It is a larger frame turbo that requires aftermarket headers, oil scavenge pump modifications, and more aggressive tuning. While spool is slower (full boost around 3,800 rpm), the top-end pull is exceptional. The FP Green is best suited for race fuel or ethanol blends and a built transmission clutch.

All three options can achieve the 330+ hp goal, but the Garrett and Blouch turbos offer the best value and simplicity for the $1,200–$1,500 price range.

Supporting Modifications

A turbo upgrade alone will not unlock 330 hp. The stock FA24 fuel system, intercooler, and exhaust are all restrictive. The following modifications are essential for reliability and power:

Fuel System Upgrades

The stock direct injection pump and injectors max out around 330–340 whp. To exceed that safely, upgrade to a high-pressure fuel pump (HPFP) from companies like Nuke Performance or Nostrum (approx. $600–$900). Alternatively, a port injection kit (IAG Performance or Radium Engineering) can supplement fuel for higher ethanol content. For a $2,500 budget, skip port injection and focus on a drop-in HPFP upgrade and larger injectors (1,500 cc+) – total cost ~$600.

Intercooler & Charge Piping

The factory top-mount intercooler heat soaks quickly on track. A front-mount intercooler (FMIC) from Process West or Turbosmart (approx. $500–$700) dramatically reduces intake temperatures. Pair it with 2.5-inch charge pipes and a blow-off valve to prevent compressor surge under high boost.

Exhaust System

The stock downpipe and muffler are heavily catalytic and restrictive. A 3-inch catless downpipe ($200–$350) and a 3-inch cat-back exhaust ($500–$800) free up high-flow potential. For maximum gains, opt for a full turbo-back system and a resonated midpipe to keep noise within reasonable limits.

Oil Cooling & Heat Management

Increased turbo heat demands better oil cooling. A larger oil cooler (Mishimoto or Setrab, $400) with a thermostatic plate maintains safe oil temperatures during sustained pulls. Also consider a turbo blanket and ceramic coating on the downpipe to keep under-hood temperatures low.

Boost Control

An electronic boost controller (e.g., Cobb 3-port or Turbosmart E-Boost) provides precise boost control and allows you to safely push the new turbo to its efficiency island. Include this in your tuning cost (typically $200–$400 for the controller plus an extra $100 for install).

Tuning Strategy

No mechanical upgrade is complete without custom tuning. The FA24’s ECU is locked, but standalone solutions like Motec (expensive) or ECUtek (common) allow full reflashing. Expect to pay $400–$800 for a remote tune from a reputable calibrator (e.g., Clark Turner, Mikey Botting, or EngineTuner). Tuning steps include:

  • Base calibration for 93-octane pump gas with reduced timing and increased fuel target.
  • Boost mapping to reach 18–20 psi on the Blouch or 22 psi on the Garrett.
  • Adjusting knock sensors, MAF scaling, and closed-loop fueling for the larger injectors.
  • Optional flex-fuel sensor if you plan to run E85 later – but this requires a separate map and additional sensor hardware (~$300).

Without a proper tune, even the best turbo upgrade will run lean and damage the engine. Always datalog the initial pulls and send them to your tuner for revision.

Cost Breakdown

Here is a realistic parts list for a 330+ hp FA24 build within a $2,500 budget:

  • Turbocharger: $1,300 (Blouch 20G XT-R includes gaskets)
  • Fuel Injectors: $250 (DeatschWerks 1,000 cc drop-in)
  • High Pressure Fuel Pump: $600 (Nostrum Stage 2)
  • Catless Downpipe: $250 (Grimmspeed or Invidia)
  • Custom Tune: $500 (ECUtek or Cobb Accessport license + remote tune)
  • Miscellaneous: $100 (intercooler couplers, gaskets, piggyback harness)

Total: $3,000 (slightly over estimate, but you can save by buying used parts or forgoing the HPFP now and tuning conservatively to 330 hp). Alternatively, swap the HPFP for a Water/Methanol injection kit ($400) which adds octane and cooling – but this is a band-aid that does not solve fuel volume limits at higher power.

Expected Performance Gains

With the above modifications and a pump-gas tune, a 330 whp and 320 lb-ft result is common. On a Dynojet, stock FA24 BRZ/GR86 reads about 270 hp at the wheels (driveline loss ~15%). After the upgrade, expect:

  • Wheel Horsepower: 330–350 whp (Dynojet).
  • Torque: 320–340 lb-ft at 3,800 rpm.
  • 0–60 mph: 4.2–4.5 seconds (vs 5.4 stock).
  • ¼-Mile: 12.2–12.5 seconds at 113–116 mph (vs 13.5 stock).

These numbers assume proper traction with sticky tires and a smooth launch. Torque increase is especially noticeable – the FA24’s twin-scroll nature keeps the car responsive even in 5th gear cruising. Keep in mind that exceeding 340 whp on the stock clutch may cause slipping; the OEM clutch holds about 300 lb-ft at the wheels reliably. Budget an extra $800–$1,200 for a clutch upgrade (ACT or Exedy) when power surpasses 350 whp.

Potential Pitfalls & Reliability Considerations

Pushing the FA24 beyond 330 hp introduces risks. Common issues include:

  • Fuel Starvation: The stock low-pressure fuel pump in the tank can become inadequate at higher fuel flow. A Walbro 525 pump ($150) is a cheap upgrade.
  • Rod Bearing Fatigue: While the FA24 rods are forged, aggressive tune calibration that overshoots torque at low rpm (e.g., 380 lb-ft at 3,000 rpm) can bend rods. Work with your tuner to shape the torque curve conservatively.
  • Heat Soak: Without an effective intercooler and oil cooling, the engine will pull timing after repeated WOT runs. Add a second auxiliary radiator if tracking the car.
  • Driveshaft Angles: The BRZ/GR86 uses a two-piece driveshaft. High torque can induce driveline vibration – consider a one-piece carbon fiber shaft if vibrations appear.

Regular oil changes with a good 5W-40 synthetic and spark plug interval reduction (every 15k miles instead of 30k) are critical. Many owners report high-mileage FA24s with 330 hp tunes surviving over 60,000 miles without major failure when maintained properly.

Conclusion

Upgrading the FA24 turbocharger from stock to 330+ horsepower is an achievable goal with an investment of approximately $2,500 to $3,000. By selecting a quality turbo like the Blouch 20G XT-R or Garrett GTX2860R, pairing it with fuel system upgrades and a custom tune, the FA24 delivers a transformative driving experience. The gains in acceleration and top-end power make the car feel significantly quicker than stock, while retaining enough low-end torque for daily driving. For enthusiasts with a modest budget and willingness to learn tuning fundamentals, the FA24 platform offers one of the best horsepower-per-dollar ratios in the current sports car market. For further reading, resources from Cobb Tuning, IAG Performance, and Driving.ca’s FA24 overview provide detailed part breakdowns and community dyno results. Start your build with a clear plan, a conservative initial tune, and a commitment to regular maintenance – the result will be a reliable, thrilling car that punches well above its weight class.