The FA24 engine has rapidly become a favorite platform for enthusiasts seeking a robust balance of daily drivability and performance potential. Found in models such as the Subaru WRX (2022+) and the Ascent, this turbocharged flat-four offers a strong foundation for modifications. Owners report substantial power gains and improved driving dynamics after carefully selected upgrades. In this article, we dive deep into real-world data from owners who have modified their FA24 engines, covering specific modifications, dyno-verified gains, and the trade-offs involved in pushing this powerplant further.

Understanding the FA24 Engine

The FA24 is a 2.4-liter, direct-injection turbocharged boxer engine. It produces 271–290 horsepower and 258–277 lb-ft of torque from the factory, depending on the application. Key features include a closed-deck block design, twin-scroll turbocharger, and a high compression ratio of 10.6:1. This combination delivers strong low-end torque while keeping efficiency reasonable for daily driving.

Compared to its predecessor, the FA20, the FA24 offers increased displacement and a more robust bottom end. The turbocharger is capable of higher boost pressures, but the factory ECU is conservative for safety and emissions compliance. This leaves significant headroom for modifications—many owners report gains of 30–60 horsepower at the wheels with bolt-on parts and a proper tune. Understanding the engine’s stock limitations and strengths is essential before selecting parts.

For a detailed technical breakdown of the FA24’s architecture, consider this guide to the FA24 engine specs.

Common Modifications for Power Gains

Owners typically begin with a staged approach: first optimizing airflow and engine management, then addressing thermal and fueling needs before tackling turbocharger upgrades. Below is an expanded look at each mod category, including typical dyno results from the community.

Cold Air Intake Systems

Cold air intakes reduce restriction and lower intake air temperatures compared to the stock airbox. On the FA24, a well-designed intake like the Cobb SF intake or the ETS intake can add 10–15 horsepower and 8–12 lb-ft of torque at peak, with broader gains in the midrange. Owners frequently note improved throttle response and a more aggressive induction sound. However, intakes require a tune to avoid a lean condition; running an untuned intake can cause knock events.

High-Performance Exhaust Systems

Exhaust upgrades offer some of the best bang-for-buck gains. A cat-back exhaust alone may yield 5–10 horsepower, but combining a downpipe (catted or catless) with a front pipe and cat-back can unlock 20–30 horsepower. The stock downpipe contains a restrictive catalytic converter that creates a major bottleneck. A high-flow downpipe paired with a tune often reveals the FA24’s true potential—many owners report reaching 300–320 whp on pump gas with just intake, downpipe, and a flex-fuel tune.

Note that removing the catalytic converter may violate emissions laws in some regions. For a deeper dive on exhaust choices, check out this exhaust guide from Subispeed.

Tuning and ECU Remapping

Regardless of hardware, a custom tune is the single most important modification. The FA24’s ECU can be reflashed via Cobb Accessport, ECUTek, or open-source software like Romraider. Stage 1 (tune only) typically adds 25–35 horsepower and 40–50 lb-ft of torque, primarily through revised boost, fuel, and timing maps. Stage 2 (intake + exhaust + tune) can reach 310–330 whp on 93 octane. On ethanol (E60 blend), some tuners have seen 370–390 whp with a stock turbo and necessary fuel system upgrades.

Owners should always choose a reputable tuner with FA24 experience. Poor tuning can lead to detonation and engine damage. The popular forum thread FA24 tuning success stories on NASIOC offers many firsthand accounts.

Upgraded Turbochargers

When stock turbo capacity is exhausted, upgrading the turbocharger is the next step. The stock unit can support around 380–400 whp on ethanol before running out of compressor efficiency. Popular upgrades include the Garrett G25-550, BorgWarner EFR 6258, or the IHI RHF5 series. Owners report 420–480 whp on pump gas (93) and over 500 whp with ethanol, provided supporting mods are in place. However, larger turbos shift the power band to higher RPM, and spool response can suffer without proper wastegate selection and tuning.

Intercooler Upgrades

The FA24’s top-mount intercooler (TMIC) can heat soak under sustained boost, reducing power and increasing intake temperatures. Upgrading to a larger TMIC (like the Process West Verticooler) or a front-mount intercooler (FMIC) lowers charge air temperatures by 20–40°F. This not only recovers lost power but also improves consistency on hot track days. Dyno tests show a gain of 10–15 horsepower on a tuned car when IATs are controlled, purely from timing advancement the ECU can safely add.

Real Owner Reports on Power Gains

To ground these numbers in real-world experience, we collected expanded reports from FA24 owners who documented their builds with dyno sheets and daily driving impressions.

  • Owner A (2022 WRX, “MikeR”): Started with a Cobb Stage 1 tune and immediately noticed smoother throttle and a 30 hp at-the-wheels gain over stock. After adding a Cobb SF intake and a cat-back exhaust (Stage 2), dyno results showed 323 whp and 326 lb-ft on 93 octane. Mike reported improved acceleration through all gears and a more responsive tip-in, though fuel economy dropped by about 2 MPG.
  • Owner B (2023 WRX, “Boosted4Life”): Installed a full turbo upgrade (Garrett G25-550) with a custom ECUTek tune, Fortified Automotive fuel pump, and 1050cc injectors. On E60 ethanol, the car put down 456 whp and 408 lb-ft. The owner noted that spool lags slightly compared to stock—full boost came at 3800 RPM instead of 3000—but the top-end pull is “addictive.” Clutch upgrades were necessary to handle the torque.
  • Owner C (Subaru Ascent, “CampingDad”): Focused on towing reliability. Added a Process West TMIC, Cobb Accessport Stage 1 tune, and a high-flow downpipe. Dyno results: 288 whp and 302 lb-ft (up from 247 whp stock). Cooling efficiency improved, reducing intake temps by 15°C on long grades. No drivability issues; fuel economy remained about the same.
  • Owner D (2022 WRX, “EarCandy”): Chose only axle-back exhaust and an intake without a tune (not recommended). The intake caused occasional lean tip-in, but the owner liked the sound. They later added a tune and gained 28 whp, bringing the total to 296 whp. The exhaust note became noticeably deeper and more aggressive.

These real-world examples illustrate the range of outcomes. Note that the gains listed are measured at the wheels; crank gains are typically 10–15% higher due to drivetrain losses.

Performance Improvements Beyond Power

Modifying the FA24 doesn’t just increase straight-line speed. Many owners report significant improvements in overall driving quality:

  • Throttle response: Aftermarket intakes and tune adjustments virtually eliminate factory throttle lag. Owners describe the pedal feel as “instant and linear.”
  • Handling and stability: Replacing heavy stock parts (such as the cast-iron downpipe with a stainless unit) sheds unsprung weight. Some owners upgrade to lightweight coilovers (e.g., Ohlins, KW) and sway bars, reducing body roll by 30% or more.
  • Driveline feel: Upgraded motor mounts and transmission bushings tighten the powertrain response, especially during hard shifts. The sensation of “flex” disappears, making the car feel more planted.
  • Exhaust note and cabin atmosphere: While subjective, the change in sound is frequently cited as one of the most rewarding aspects—owners describe a deeper, more aggressive tone that still remains civil at cruising speeds.

These secondary benefits often contribute as much to the enjoyment of the car as the raw horsepower increase.

Considerations for Modifications

Every modification comes with trade-offs. Here are the key factors every FA24 owner should weigh before proceeding.

Warranty Implications

Any modification that alters engine management or drivetrain components can void portions of the manufacturer’s warranty. In the United States, the Magnuson-Moss Warranty Act protects consumers, but dealers may deny claims if aftermarket parts are proven to have caused a failure. Some owners choose to wait until the warranty expires, while others accept the risk.

Reliability and Engine Longevity

The FA24’s closed-deck block is robust, but adding power increases stress on pistons, rods, and bearings. Moderately tuned cars (up to ~350 whp) often last 100,000+ miles with proper maintenance and good fuel. Beyond 400 whp, supporting mods like forged rods, stronger pistons, and a better oil pump become advisable. Owners who track their cars should monitor oil temperatures and consider an oil cooler.

Removing catalytic converters, disabling O2 sensors, or using emissions-defeating tunes is illegal in many jurisdictions. These actions can lead to failed inspections and fines. For daily drivers, consider high-flow catted downpipes rather than catless options. Some tuners offer “eco” maps that reduce power but keep emissions in check.

Cost vs. Reward

Building a reliable 450+ whp FA24 typically costs $8,000–$12,000 in parts, labor, and tuning. A simple Stage 1 tune can be done for under $700 and yields a satisfying 30-40 hp gain. Owners should set realistic budgets and goals. Many find that a Stage 2 setup (intake, downpipe, tune) offers the best balance of performance and value.

Common Pitfalls to Avoid

  • Skimping on tune: Using off-the-shelf maps without custom calibration can cause knock or lean conditions. Always get a dyno or road tune from an experienced FA24 tuner.
  • Ignoring fuel requirements: Higher boost requires higher octane. On pump gas, careful knock monitoring is essential. Ethanol blends offer a safety margin but require injector and pump upgrades.
  • Overlooking cooling: Without adequate intercooling and oil cooling, sustained hard driving can lead to power loss and engine damage.
  • Neglecting driveline: Stock clutches and mounts can fail under high torque. A simple clutch upgrade (e.g., ACT, Exedy) is recommended for builds exceeding 350 lb-ft.

Conclusion

The FA24 engine offers a sturdy platform for those seeking more power and sharper performance. Through careful selection of modifications—starting with intake, exhaust, and a professional tune—owners consistently report gains of 30–50 wheel horsepower while retaining daily drivability. For those who want to push further, turbo upgrades and ethanol support unlock 400+ whp, albeit with increased investment and maintenance demands.

As with any performance project, informed decisions and realistic expectations yield the best results. Research thoroughly, consult owners on dedicated forums, and work with reputable tuners and shops. The FA24 community continues to grow, and the shared knowledge base makes it easier than ever to build a capable, reliable, and exciting car. Whether you stick with Stage 1 or build a 500 whp monster, the journey is part of the reward.