Introduction to FA20 Turbo Upgrades for the Subaru WRX

The Subaru WRX has carved out a loyal following since its introduction, blending rally-bred all-wheel drive with turbocharged performance that punches above its weight. The FA20 engine, found in the 2015 and later WRX models, represents a significant evolution from the earlier EJ series, offering direct injection, a twin-scroll turbocharger, and improved thermal efficiency. This combination makes the FA20 a compelling platform for enthusiasts who want to extract more power without sacrificing daily drivability.

When it comes to increasing horsepower and torque, the turbocharger is the single most impactful component you can upgrade. The decision between staying with the stock turbocharger or moving to an aftermarket unit involves trade-offs in cost, complexity, power delivery, and reliability. This article delivers a detailed, data-driven comparison of power gains achievable with the stock FA20 turbo versus popular aftermarket turbochargers, along with the supporting modifications and tuning strategies you need to know.

Understanding the FA20 Engine Architecture

The FA20F (the turbocharged variant) is a 2.0-liter flat-four engine with a bore and stroke of 86 mm x 86 mm, giving it a perfectly square design. It features a compression ratio of 10.6:1, which is relatively high for a turbocharged engine, and relies on direct injection to manage knock resistance and improve efficiency. The twin-scroll turbocharger is integrated into the exhaust manifold to reduce lag and improve spool characteristics, which is a key reason the stock turbo feels responsive from low RPM.

The engine's closed-deck design in later model years and robust oiling system make it capable of handling increased power, but the connecting rods and pistons become a limiting factor beyond approximately 400 wheel horsepower on pump gas. Understanding these mechanical boundaries is essential when planning a turbo upgrade, because exceeding them without internal reinforcement can lead to catastrophic failure.

Direct injection on the FA20 also means that port injection or upgraded low-pressure fuel pumps may become necessary when pursuing substantial power gains, as the stock high-pressure fuel pump can run out of capacity at higher fuel demands. This nuance is often overlooked in basic turbo comparison articles, but it directly affects how much power you can realistically achieve with any turbocharger.

Stock Turbocharger Performance and Limitations

The stock turbocharger on the FA20 WRX is a Mitsubishi TF18 or similar twin-scroll unit, which produces a peak boost pressure of approximately 16.5 psi from the factory. This results in Subaru's advertised output of 268 horsepower and 258 lb-ft of torque at the crank. On a chassis dynamometer, typical stock wheel horsepower numbers fall between 195 and 210 hp, depending on the fuel, ambient conditions, and drivetrain losses.

While the stock turbo provides excellent spool characteristics with boost building as early as 2,500 RPM and full boost by 3,000 RPM, it runs out of airflow capacity at higher RPM. The turbine housing and compressor wheel are optimized for quick response rather than peak power, which means the stock turbo becomes a bottleneck above approximately 5,500 RPM. This is why even with aggressive tuning, the stock turbo tends to deliver a torque-heavy powerband that drops off up top.

Reliability is a strong suit of the stock setup. The turbo is well-matched to the engine's thermal and airflow requirements, and Subaru's factory calibration includes generous safety margins. However, the stock intercooler is air-to-air and heat-soaks quickly under sustained load, which limits consistency on track days or during aggressive back-to-back pulls. Upgrading the intercooler is one of the most effective first steps, even if you plan to keep the stock turbo.

Power Gains Achievable with Stock Turbo and Modifications

With the stock turbo retained, you can still achieve meaningful power gains through complementary modifications and professional tuning. The most common package includes an aftermarket intercooler or charge air cooler, a high-flow intake, a cat-back or turbo-back exhaust, and an electronic boost control solenoid for more precise boost management. Combined with a custom tune using a Cobb Accessport or open-source software like EcuTek, the typical results are:

  • Wheel horsepower: 250 to 270 whp (approximately 300 to 320 crank horsepower)
  • Wheel torque: 270 to 290 lb-ft (approximately 320 to 350 crank lb-ft)
  • Peak boost: 20 to 22 psi

These gains are achieved without altering the turbocharger itself, which keeps costs relatively low and retains the OEM-like spool response. The torque increase is particularly noticeable in the mid-range, making the car feel significantly faster in everyday driving. However, the power still falls off after 5,500 RPM, so this setup is ideal for street use and autocross where low-end response matters more than top-end horsepower.

It is important to note that even with these mods, the stock turbo is still the limiting factor for top-end airflow. If your goal is to exceed 300 wheel horsepower, you will need to consider an aftermarket turbocharger.

Aftermarket Turbocharger Options for the FA20

The aftermarket turbocharger landscape for the FA20 WRX offers a wide range of choices, from direct bolt-on replacements that improve upon the stock unit to large-frame turbos that require extensive supporting modifications. The most popular and well-documented options come from Garrett, BorgWarner, and ETS (Extreme Turbo Systems). Each brand has distinct characteristics in terms of spool speed, airflow capacity, and power potential.

Garrett GTX2860R Gen II is a popular direct upgrade that offers a higher-flowing compressor wheel while retaining a similar turbine housing size. It spools almost as fast as the stock turbo but supports up to approximately 400 wheel horsepower with proper fueling. This makes it an excellent choice for those who want a significant power increase without sacrificing daily drivability.

BorgWarner EFR 6258 and 6758 are favorites among serious enthusiasts due to their advanced metallurgy and integrated recirculation valves. The EFR series offers exceptional response and efficiency, with the 6258 supporting around 450 wheel horsepower and the 6758 capable of over 500 wheel horsepower. These turbos require a custom downpipe and intake piping, and they benefit from an external wastegate for precise boost control.

ETS (Extreme Turbo Systems) offers complete turbo kits that include the turbocharger, exhaust manifold, downpipe, and intercooler piping. Their turbo options range from 3.5-inch inlet to 4-inch inlet units, with power capabilities spanning from 400 to over 600 wheel horsepower. These kits are engineered for maximum flow and are typically paired with upgraded fuel systems and engine management.

Other notable mentions include the Blouch Dominator series, which has a strong reputation in the Subaru community, and the Precision Turbo 5431 EFR, which offers a balance of cost and performance. Regardless of brand, all aftermarket turbos require careful attention to oil lines, coolant lines, and heat shielding to ensure reliability.

Performance Gains with Aftermarket Turbochargers

The power potential with an aftermarket turbo depends largely on the size of the unit and the extent of supporting modifications. Below are realistic power ranges for common aftermarket turbo setups on the FA20 engine with 93 octane pump gas and proper tuning:

  • Garrett GTX2860R Gen II: 350 to 400 wheel horsepower, 350 to 380 lb-ft wheel torque
  • BorgWarner EFR 6258: 400 to 450 wheel horsepower, 380 to 420 lb-ft wheel torque
  • ETS 3.5-inch kit: 450 to 500 wheel horsepower, 420 to 460 lb-ft wheel torque
  • BorgWarner EFR 6758 or larger: 500 to 550 wheel horsepower, 470 to 520 lb-ft wheel torque

These figures assume the use of an upgraded intercooler, high-flow intake and exhaust, upgraded fuel injectors (at least 1,000 cc), and a high-flow fuel pump. Above 450 wheel horsepower, the stock direct injection system often requires supplementation with port injection or a fuel pump upgrade to maintain adequate fuel pressure. Additionally, the stock connecting rods and pistons become a significant risk factor at power levels exceeding 450 wheel horsepower on pump gas, and many builders recommend forged internals for sustained high-power use.

Boost levels with aftermarket turbos typically range from 22 to 28 psi, depending on the turbo size and fuel quality. Spool characteristics vary: smaller frame turbos like the GTX2860R reach full boost by 3,500 RPM, while larger units like the EFR 6758 may not reach full boost until 4,200 RPM or higher. This trade-off between peak power and response is the central consideration when choosing an aftermarket turbo.

Key Factors to Consider When Upgrading

Choosing between the stock turbo and an aftermarket unit is not simply a matter of peak power numbers. Several practical factors will influence which path is right for your specific goals, budget, and use case.

Budget and Total Cost of Ownership

The stock turbo path is the most cost-effective. An intercooler, intake, exhaust, and tune can be completed for under $3,000, and you retain OEM reliability and emissions compliance. In contrast, an aftermarket turbo upgrade with all necessary supporting mods often ranges from $5,000 to $10,000 or more, especially if you include engine internals for higher power levels. Installation labor adds significant cost if you are not performing the work yourself.

Power Delivery and Driving Experience

If you value immediate throttle response and a torque-rich feel in daily driving, the stock turbo with a tune offers an excellent experience. If you are chasing high-speed power for track days, drag racing, or road course work, an aftermarket turbo that maintains power to redline is a better fit. Test driving a car with each setup before purchasing can be very revealing.

Reliability and Longevity

Stock turbo setups are proven to be reliable for 100,000+ miles with proper maintenance. Aftermarket turbos place more stress on the engine, and the risk of failure increases with power level. Oil quality, cooling system upgrades, and conservative tuning are critical for long-term reliability with any aftermarket turbo. Engines built for 450+ wheel horsepower typically require shorter maintenance intervals and higher operating costs.

Supporting Modifications Required

An often underestimated aspect of turbo upgrades is the list of supporting modifications. Beyond the turbo itself, you will likely need:

  • Upgraded intercooler (air-to-air or air-to-water for high power)
  • High-flow intake and turbo-back exhaust
  • Electronic boost control solenoid or external wastegate
  • Upgraded fuel injectors and fuel pump
  • High-flow fuel pressure regulator for E85 applications
  • Oil cooler and possibly an upgraded radiator for sustained use
  • Engine management tuning (Cobb Accessport or EcuTek)
  • Optional: forged pistons and rods for power above 450 whp

Failing to address any of these supporting items can lead to reduced performance, drivability issues, or engine damage. A common mistake is installing a large turbo without upgrading the fuel system, which causes lean conditions under boost and risks detonation.

Tuning Considerations for Stock and Aftermarket Turbos

Tuning is the most critical factor in safely achieving power gains with either turbo path. The FA20 engine is sensitive to knock due to its high compression ratio and direct injection. Professional tuning using a reputable platform is not optional; it is essential for engine longevity.

For stock turbo setups, the tuner will optimize boost targets, ignition timing, air-fuel ratios, and variable valve timing to maximize torque without exceeding the turbo's efficiency island. The result is a smooth, linear power curve that feels strong throughout the RPM range. Many tuners also adjust throttle mapping and launch control for an improved driving experience.

For aftermarket turbo setups, tuning becomes more complex. The larger turbo moves more air, requiring changes to MAF scaling, injector latency, and boost control strategy. Flex fuel tuning (E85) is popular with aftermarket turbos because ethanol's higher octane allows for more aggressive timing and higher boost, often yielding 15–25% more power than pump gas. However, E85 requires upgraded fuel system capacity and careful monitoring of fuel trims.

Data logging and iterative tuning are standard practice. A well-tuned aftermarket turbo car will have consistent air-fuel ratios (targeting 11.5:1 for pump gas), safe exhaust gas temperatures (below 1,600°F sustained), and minimal knock correction. It is worth investing in a tuner who has specific experience with the FA20 platform, as the direct injection system and twin-scroll manifold present unique tuning challenges.

For further reading on tuning strategies and turbo selection, consult resources like Cobb Tuning for Accessport support and EcuTek for advanced calibration options. Additionally, the NASIOC forums provide extensive community knowledge on FA20 turbo upgrades.

Final Verdict: Stock Turbo vs Aftermarket Turbo

The decision between keeping the stock turbocharger and upgrading to an aftermarket unit depends entirely on your performance objectives, budget, and tolerance for added complexity. For most daily drivers who want a noticeable increase in power without sacrificing reliability or drivability, the stock turbo with a tune and supporting bolt-ons is the smart choice. It delivers a strong, responsive powerband that transforms the car's character without breaking the bank or requiring constant maintenance.

For enthusiasts who are building a dedicated performance car, compete in time attack or drag racing, or simply want the satisfaction of extracting maximum potential from the FA20 platform, an aftermarket turbo upgrade offers headroom that the stock unit simply cannot match. With proper planning, quality parts, and expert tuning, aftermarket turbos can provide exhilarating performance that rivals cars costing significantly more.

Whichever path you choose, invest in a high-quality tune, use the best fuel available, and maintain your engine meticulously. The FA20 platform rewards careful modification with miles of driving enjoyment, and understanding the trade-offs between stock and aftermarket turbochargers is the first step toward building a WRX that meets your exact vision.