Introduction: The 320+ RWHP Goal for Your Turbocharged BRZ

The Subaru BRZ has carved out a unique place in the automotive world as a lightweight, rear-wheel-drive sports car that rewards driver skill. Its naturally aspirated FA20 flat-four engine is a willing partner for forced induction, and a carefully selected turbocharger can transform the car’s character without compromising its balance. For many enthusiasts, the magic number is 320 wheel horsepower (RWHP) – a threshold that pushes the BRZ from quick to genuinely fast while maintaining everyday usability. A 72mm turbo is a popular choice for this power level, offering a balance of response and peak output. However, hitting that number reliably requires more than just bolting on a turbo and turning up the boost. This article details the tuning strategies, component choices, and supporting modifications needed to achieve 320+ RWHP with a 72mm turbo on a BRZ, ensuring your build is both powerful and durable.

Understanding the BRZ Platform for Turbocharging

The FA20 engine in the BRZ is a robust foundation, but its design was optimized for naturally aspirated operation. Key characteristics that influence turbocharging include a high 12.5:1 compression ratio, direct injection, and an aluminum block with open-deck construction. While the engine can handle moderate boost, pushing to 320+ RWHP demands careful attention to fuel requirements, thermal management, and internal strength. The direct injection system can provide excellent fuel atomization at low and mid loads, but at higher power levels the stock fuel pump and injectors run out of capacity. Additionally, the factory engine control unit (ECU) has limited ability to manage boost targets, fuel trims, and ignition timing under forced induction. For these reasons, a comprehensive approach to tuning – covering engine management, fuel delivery, cooling, and exhaust flow – is non-negotiable.

Choosing the Right 72mm Turbocharger

A "72mm turbo" typically refers to the size of the compressor inducer. This class of turbocharger can support 400 to 550 crank horsepower depending on the specific trim, turbine housing, and supporting setup. For a BRZ targeting 320+ RWHP, a well-matched 72mm unit will spool reasonably while delivering ample top-end flow. When evaluating options, consider the following factors:

  • Compressor map efficiency: Ensure the turbo operates in its highest efficiency islands at your target boost and RPM. A 72mm compressor like the Garrett GTX3076R Gen II or BorgWarner EFR 7163 offers excellent efficiency across a broad range.
  • Turbine housing AR (area/radius): A smaller AR (e.g., 0.63) improves low-end response but can choke power at high RPM. For 320+ RWHP, a 0.82 or 0.85 AR is often ideal with a 72mm compressor, allowing strong mid-range and headroom for higher boost.
  • Internal vs. external wastegate: For precise boost control at this power level, an external wastegate is highly recommended. It reduces boost creep and allows more stable tuning.
  • Ball bearing vs. journal bearing: Ball bearing turbos (like those from Garrett or BorgWarner) spool faster and offer better transient response, which is especially beneficial on the relatively small-displacement FA20.

Popular choices for 320+ RWHP include the Garrett GTX3076R (with a 0.82 AR T3 turbine housing) and the BorgWarner EFR 7163 with an internal or external wastegate setup. Both provide a good compromise between quick spool and top-end power.

Engine Preparation: Strengthening the FA20 for 320+ RWHP

While the FA20 can survive 320 RWHP on a conservative tune with stock internals, reliability at this level is marginal. To build an engine that handles sustained pulls and track use, consider these upgrades:

Forged Pistons and Connecting Rods

Stock pistons are cast aluminum and can fracture under high cylinder pressures. Forged pistons (e.g., from Manley, JE, or CP-Carrillo) offer greater strength and improved heat rejection. Pair them with forged connecting rods (Manley, Eagle, or K1) to handle the additional stresses of forced induction. A common compression ratio target for turbo builds is 9.0:1 to 9.5:1, which allows more boost while reducing detonation risk.

Head Gasket and Studs

Upgrading to a multi-layer steel (MLS) head gasket and ARP head studs is essential for maintaining a reliable seal at elevated boost levels. This prevents head lift and coolant loss, which can lead to catastrophic failure.

Oil System

The FA20's oiling system can be stressed under track conditions. An oil cooler (see section below), a baffled oil pan, and possibly a high-volume oil pump can help maintain consistent oil pressure. Consider a dual-oil cooler setup for high-heat environments.

Note: Many tuners have achieved 320+ RWHP on a stock long-block with careful tuning, but the safety margin is thin. For a long-lived build, forged internals are strongly advised.

Tuning Strategies for 320+ RWHP

Achieving smooth, safe, and powerful operation at this power level requires a comprehensive tuning approach. The key areas are engine management, fuel control, ignition timing, and boost management.

1. Engine Management System (EMS)

The factory ECU can be reflashed (via ECUTek or similar) to handle moderate boost, but for 320+ RWHP a standalone EMS is a significant advantage. Standalone systems like Motec M1, Haltech Elite 2500, or Link Fury offer complete control over fuel, ignition, boost, and knock detection. They also allow for advanced features such as:

  • Closed-loop boost control: Dynamically adjusts wastegate duty to maintain target boost across varying conditions.
  • Anti-lag and launch control: Optimize spool and acceleration.
  • Flex fuel capability: Tune for ethanol blends (E85) to achieve 320+ RWHP more easily with added knock resistance.
  • Data logging with high resolution: Monitor knock, exhaust gas temperature (EGT), lambda, and more to fine-tune.

If you prefer to retain the factory ECU, ECUTek with a custom calibration from a reputable tuner can work, but be aware of the limitations regarding boost control and data resolution. Many successful 320+ RWHP builds use ECUTek with a separate boost controller.

2. Fuel System Upgrades

Stock fuel system components become the bottleneck at this power level. To deliver sufficient fuel volume and maintain proper pressure, upgrade as follows:

  • Fuel injectors: Use 1000-1300cc/min direct-injection compatible injectors (e.g., Injector Dynamics ID1050x or Fuel Injector Clinic 1000cc). These can support up to 400+ RWHP on E85 or 300+ on pump gas.
  • Fuel pump: A high-flow in-tank pump like the AEM 340lph or Walbro 525 is necessary. For very high power, consider a surge tank and external pump setup.
  • Fuel pressure regulator: Use an adjustable regulator (e.g., Aeromotive A1000) to set base pressure and maintain consistent flow.
  • Flex fuel sensor: Installing a flex fuel sensor (e.g., Zeitronix or GM style) allows tuning for any ethanol blend, reducing knock risk and enabling more aggressive timing.

Proper fuel tuning requires a wideband oxygen sensor (lambda) to verify AFRs. Target an air-fuel ratio of 11.5:1 to 12.0:1 for gasoline at high load; for E85, target 7.0:1 to 7.8:1 (lambda ~0.78).

3. Ignition Timing and Knock Management

Boosted engines are knock-limited. At 320+ RWHP, you need to run conservative ignition timing to avoid detonation, especially on 91 or 93 octane pump gas. Typical timing at peak torque ranges from 10° to 15° BTDC under boost, tapering to 18°-22° at redline. Use a knock detection system (factory knock sensor or aftermarket module) to actively retard timing in response to knock events. Standalone ECUs can incorporate knock control strategies that automatically pull timing on a per-cylinder basis.

4. Boost Control and Target Strategy

A common method is to use a three-port boost solenoid (e.g., Mac valve) controlled by the EMS. For a 72mm turbo targeting 320+ RWHP, boost levels typically fall between 12 psi and 18 psi, depending on turbo efficiency, compression ratio, and fuel octane. On 93 octane, 14-16 psi is common; on E85, 16-18 psi is possible with proper tuning. Work with your tuner to develop a boost curve that provides linear power delivery – a sharp onset can overwhelm the tires and drivetrain.

Exhaust System Optimization

The exhaust path has a direct effect on turbo spool, backpressure, and power potential. For a 72mm turbo build, consider these components:

  • Equal-length header: While equal-length headers help with scavenging on NA engines, for turbo applications an unequal-length header (UEL) can provide better cylinder-to-cylinder flow distribution and earlier spool. Both options work; discuss with your fab shop.
  • Downpipe: A 3-inch stainless steel downpipe with a high-flow catalytic converter (or catless for high power) minimizes restriction. Ensure a wastegate dump tube vents separately to avoid turbulence.
  • Cat-back exhaust: A 3-inch cat-back system (e.g., from Invidia, HKS, or GReddy) reduces backpressure and provides a pleasant exhaust note. Avoid excessive muffling that could choke flow.
  • Turbine housing selection: As noted, an A/R of 0.82 is common for a 72mm turbo on this engine. For a more street-oriented build, a 0.63 A/R spools faster but may limit top-end to around 320-340 RWHP.

An external wastegate (38mm to 44mm) with a screamer pipe or recirculated dump ensures stable boost control. Tial or Turbosmart wastegates are proven.

Cooling Solutions for Sustained Performance

Turbocharged BRZs generate significant heat, especially during back-to-back pulls or track sessions. Inadequate cooling can lead to intake air temperature (IAT) rise, detonation, and power loss. The following upgrades are critical for reliable 320+ RWHP operation:

Intercooler

For a 72mm turbo, a front-mount intercooler (FMIC) with a core size of roughly 24x12x4 inches is sufficient. Look for a bar-and-plate design with efficient fin density. Key brands include PRL, Mishimoto, or Aero Flow. Ensure ducting is sealed to the radiator pack to force air through the core.

Oil Cooler

A sandwich-plate style oil cooler with a 19- to 25-row core (e.g., Setrab, HKS, or GReddy) helps keep oil temperatures below 250°F under load. Mount the cooler in front of the radiator for maximum airflow. Use an oil thermostat to maintain proper warm-up.

Radiator and Cooling Fans

Consider a full-size aluminum radiator (e.g., Koyo or CSF) with upgraded electric fans. A 3-row radiator provides additional heat rejection. If you run an FMIC, relocate the coolant overflow tank or consider a slim fan setup to maintain clearance.

Water-Methanol Injection

For additional cooling and knock suppression, water-methanol injection can be used. A system like the Aquamist HFS-4 or Snow Performance Stage 2 injects a water/methanol mixture (50/50) into the intake stream. This can reduce IAT by 30-50°F and allow more aggressive timing, useful for achieving 320+ RWHP on pump gas without forged internals.

Drivetrain and Supporting Modifications

Power is only useful if you can put it to the ground without breaking your gearbox or differential. At 320+ RWHP, the stock BRZ drivetrain is near its limit. Consider the following enhancements:

  • Clutch: An upgraded clutch (e.g., Exedy Stage 2 or OS Giken) is necessary to handle the torque without slipping. For daily driving, a single-plate organic or ceramic disc is reasonable; for track use, a twin-disc offers better clamping force without heavy pedal feel.
  • Flywheel: Lighter flywheels improve throttle response but can increase idle vibration. A 12-15 lb flywheel is a good compromise.
  • Differential: The stock open differential will struggle to put power down. A limited-slip differential (LSD) from Cusco, Tomei, or OS Giken is recommended for controlled corner exits.
  • Axles and half-shafts: At sustained high torque, stock axles can fail. Upgraded axles (e.g., from DriveShaft Shop) provide a safety margin.
  • Tires: Choose performance tires with at least 200 treadwear (e.g., Michelin Pilot Sport 4S, Bridgestone Potenza RE-71RS) to handle the power. A 245/35R18 or 255/35R18 tire on 18x9 wheels works well.

Tuning Methodology: Dyno vs Street

Performing the final tuning is best done on a chassis dynamometer – this allows safe, repeatable, and safe load application while monitoring air-fuel ratios, boost, and knock. Dyno tuning also provides accurate horsepower numbers. However, street tuning is possible with a skilled tuner and a wideband, but it is slower and riskier. For 320+ RWHP, a dyno session with a professional is the recommended path.

During the dyno session, the tuner will create multiple fuel and timing maps for different load cells, then optimize boost control. Be prepared to spend several hours to get the tune dialed in. The result should be a smooth, linear torque curve that builds from 3000-3500 rpm and pulls to redline without any hiccups.

External Resources and Further Reading

For more detailed technical information, consult these reputable sources:

Final Thoughts

Reaching 320+ RWHP in a turbocharged BRZ with a 72mm turbo is not only achievable but can be done in a manner that retains everyday drivability and reliability. The key is a systematic approach: select a turbo that matches your power goals and driving style, strengthen the engine with forged internals for peace of mind, upgrade the fuel system to feed the additional air, tune meticulously with a standalone EMS, and address heat management with proper intercooling and oil cooling. Do not overlook the drivetrain – a strong clutch, LSD, and good tires will transform the driving experience. While the project requires investment in both parts and professional tuning, the result – a responsive, powerful, and reliable BRZ that still loves corners – is well worth the effort.

Whether you are building a weekend warrior or a dedicated track car, the strategies outlined here provide a clear roadmap. Work closely with a tuner experienced in turbo FA20 builds, and always prioritize safety and durability over peak numbers. With the right components and careful calibration, your 72mm turbo BRZ can achieve that 320+ RWHP goal and deliver smiles for many miles.