FA20 Engine Overview

The FA20 family is a 2.0‑liter flat‑four engine developed by Subaru. It exists in two major configurations: the naturally aspirated version found in the Subaru BRZ, Scion FR‑S, and Toyota GT86 (producing around 200 hp and 151 lb‑ft), and the turbocharged FA20DIT variant used in the Subaru WRX (2015+), Levorg, and some international models, which delivers approximately 268 hp and 258 lb‑ft from the factory. The turbocharged version is the primary platform for the Garrett GTX upgrades discussed here, though the NA version can also be converted with a complete aftermarket turbo kit.

Key specifications of the FA20DIT include a 9.5:1 compression ratio, dual‑scroll turbocharger, direct injection, and a closed‑deck cylinder block for high‑boost tolerance. Its compact layout and robust bottom end make it an excellent candidate for power‑adder upgrades.

Why Choose Garrett GTX Series Turbochargers?

Garrett Motion (formerly Honeywell Turbo Technologies) has long set the standard for aftermarket turbochargers. The GTX series builds on the legendary GT line with a number of engineering improvements:

  • Extended‑tip compressor wheels – Reduce turbulence and improve flow efficiency, yielding faster spool and higher peak airflow.
  • High‑temperature alloy turbine housings – Withstand extreme exhaust gas temperatures (EGTs) common on highly tuned FA20 engines.
  • Low‑inertia billet compressor wheels – Improve transient response and reduce lag.
  • Larger, more efficient bearing systems – Journal bearing or ball‑bearing options offer durability at high shaft speeds.

These characteristics translate directly into real‑world gains: a properly matched GTX turbo can add 100–300+ wheel horsepower while maintaining drivability, provided supporting modifications are in place.

Each GTX model targets a specific power band and build philosophy. We’ll cover the three most common choices, from street‑friendly to all‑out race.

Garrett GTX2860R

The GTX2860R is the go‑to upgrade for drivers who want a substantial power increase without sacrificing low‑end responsiveness. Its 50‑mm inducer compressor wheel flows up to 48 lb/min, supporting roughly 300–400 hp at the wheels on a properly tuned FA20DIT. Spool is close to the stock twin‑scroll feel; full boost often arrives by 3300–3500 rpm. This makes it ideal for daily driving, street pulls, and occasional autocross or track days.

  • Power range: 300–400 whp (with fuel system and tune)
  • Boost threshold: ~3300 rpm (2.5 PMax)
  • Ideal supporting mods: 3″ downpipe, larger intercooler, fuel pump upgrade

Garrett GTX3071R

Moving up, the GTX3071R uses a 54‑mm inducer wheel with a 71‑mm exducer, flowing up to 58 lb/min. This turbo unlocks 400–500 whp potential, making it a favorite for weekend track warriors and high‑power street builds. Spool is slightly delayed compared to the GTX2860R — expect full boost around 3700–3900 rpm. The trade‑off is a stronger top‑end pull that keeps pulling well past 7000 rpm.

  • Power range: 400–500 whp
  • Boost threshold: ~3700 rpm
  • Supporting mods required: Port injection or upgraded direct injectors, fuel pressure regulator, upgraded intercooler, intake, exhaust, and a stronger clutch (if manual)

Garrett GTX3582R

The GTX3582R is a serious piece of hardware, featuring a 61‑mm inducer and an 82‑mm exducer compressor wheel that can flow over 70 lb/min. When well supported, it can push FA20 engines beyond 500 whp — and some builds have cracked 600 whp on race gas or E85. This turbo is large: spool happens around 4000–4200 rpm, and it pulls hard to redline. It requires extensive supporting modifications and is best suited to purpose‑built race cars or extremely aggressive street cars.

  • Power range: 500–600+ whp
  • Boost threshold: ~4000 rpm
  • Supporting mods: Built engine (forged rods/pistons), huge intercooler, meth/E85 injection, standalone ECU or highly custom tune, upgraded valvetrain

Supporting Modifications

Installing a Garrett GTX turbo is only the beginning. The FA20’s fuel system, intake, exhaust, and engine management must all be upgraded to match the increased airflow.

Fuel System Upgrades

The factory fuel pump and injectors on the WRX (FA20DIT) are adequate for about 300 whp pump gas. For anything beyond the GTX2860R’s lower range, you’ll need:

  • A high‑flow in‑tank fuel pump (e.g., AEM 340 or Walbro 525)
  • Larger injectors – either upgraded direct‑injection units for the WRX/BRZ turbo platform, or a port‑injection secondary system
  • Flex‑fuel sensor and tune for E85 (which provides knock resistance and allows higher boost)

Intake and Exhaust

A larger, smooth‑flowing cold‑air intake helps the turbo breathe. A 3‑inch turbo‑back exhaust (downpipe and cat‑back) is nearly mandatory. Keep the exhaust free of restrictions – a 3.5″ system may be needed for 500+ whp builds.

Charge Air Cooling

The stock top‑mount intercooler (TMIC) becomes a heat sink at higher power levels. A front‑mount intercooler (FMIC) kit or a larger bar‑and‑plate TMIC is strongly recommended. For extreme builds, water‑methanol injection can further reduce intake temperatures and suppress knock.

Drivetrain and Clutch

Upgraded turbo power will overwhelm the stock clutch on manual transmissions. A stage‑2 or stage‑3 clutch (e.g., ACT, Exedy, or South Bend) is necessary from the 300 whp level upward. Automatic WRX owners should consider a transmission cooler and upgraded valve body.

Tuning Requirements

A canned “off‑the‑shelf” map will not suffice for a GTX turbo. Professional dyno tuning or a carefully datalogged e‑tune is essential. The FA20DIT’s direct‑injection system introduces additional complexity: the high‑pressure fuel pump (HPFP) requires careful monitoring, and injection timing must be adjusted to prevent fuel dilution. A Cobb Accessport (or equivalent) with a custom tune from a known WRX tuner is the standard path. For the GTX3582R and above, a standalone ECU like a MoTeC or Haltech may be required to manage the upgraded fuel system and boost control.

Installation Considerations

Fitting a Garrett GTX turbo onto an FA20 is not a direct bolt‑on. The factory twin‑scroll manifold on the FA20DIT uses a specific flange pattern; typically, you’ll need an adapter plate or an aftermarket up‑pipe designed for T3/T4 flanges. Oil feed and drain lines must be rerouted, and a separate coolant line may be needed for water‑cooled Garrett units. Most shops recommend replacing gaskets and studs with ARP hardware. A turbo blanket and heat shielding also help keep under‑hood temperatures in check.

Professional installation is strongly advised, especially for those unfamiliar with turbo swaps. Mistakes in oil drain routing or wastegate setup can lead to oil leaks, boost creep, or turbo failure.

Power Potential and Real‑World Results

To give a clearer picture, here are typical dyno figures from well‑sorted FA20DIT builds using Garrett GTX turbos:

  • GTX2860R – 340–380 whp on 93 octane; 400+ whp on E85 (stock bottom end ok)
  • GTX3071R – 420–490 whp on 93 octane; 500 whp on E85/race gas (forged pistons recommended above 450 whp)
  • GTX3582R – 500–560 whp on pump gas; 600+ whp on E85/race gas (built engine mandatory)

These numbers assume a strong tune and appropriate supporting parts. Street drivability on the GTX2860R remains excellent; the larger turbos require more commitment but reward with visceral acceleration.

Alternative Turbo Options

While the GTX series is our focus, other turbos also deserve mention. The BorgWarner EFR 6258 offers fast spool similar to the GTX2860R, and the Precision 5431 is another popular “mid‑frame” choice. For budget‑minded builders, used Garrett GT3076R (non‑GTX) units can be found and still make 400 whp. However, the GTX’s efficiency gains often make the extra cost worthwhile.

Conclusion and Further Reading

The Garrett GTX family offers an impressive ladder of power upgrades for the FA20 engine, whether you own a WRX, BRZ with a turbo kit, or Levorg. By matching the turbo size to your horsepower goals and supporting mods, you can transform the car’s character without sacrificing reliability. As with any major power upgrade, invest in professional tuning, quality parts, and careful installation.

For additional information, check out Garrett Motion’s official product pages: GTX Series Overview. Real‑world build logs can be found on forums such as IWSTI’s FA20 section and NASIOC’s FA20DIT forum. Tuning guides from reputable shops like Summit Racing also offer turbo selection charts. Remember: the right turbo comes from understanding your driving style and end goals. Choose wisely, tune carefully, and enjoy the flat‑four fury.