The Subaru FA20 Engine: A Strong Foundation for Boost

The Subaru FA20 engine, found in models like the BRZ, FR-S, and FT86, is a 2.0-liter naturally aspirated boxer-four known for its high-revving character and flat torque curve. While it delivers a satisfying driving experience from the factory, many enthusiasts quickly find themselves wanting more power. The FA20's closed-deck block, forged connecting rods (in later revisions), and dual AVCS (Active Valve Control System) make it a surprisingly robust platform for forced induction. However, bolt-on turbo kits for the FA20 can be expensive, often exceeding several thousand dollars. The BorgWarner EFR 6758 turbocharger has emerged as a compelling budget-friendly option that delivers impressive results without demanding a second mortgage.

Why the BorgWarner EFR 6758 Turbo Stands Out

The BorgWarner EFR (Engineered For Racing) 6758 is a small-frame turbo that punches well above its weight. Its popularity in the Subaru FA20 community stems from a combination of engineering excellence and real-world performance characteristics that suit the engine's displacement and power goals perfectly.

Compact and Lightweight Design

The EFR 6758 is designed with a compact 58mm compressor inducer and a 68mm turbine exducer. This small footprint allows it to fit into tight engine bays without requiring major modifications to the frame or firewall. Weighing in at roughly 14 pounds (complete with the integrated wastegate and BOV), the EFR 6758 reduces rotational inertia and unsprung weight compared to larger frame turbos, helping maintain the FA20's nimble handling.

Integrated Bypass Valve and Wastegate

A standout feature of the EFR series is the fully integrated recirculating bypass valve and a single scroll, diaphragm-actuated wastegate. This integration simplifies installation, reduces the number of hoses and fittings, and ensures reliable boost control. The recirculating valve also helps maintain drivability and steady airflow during part-throttle transitions, which is critical for daily-driven turbo FA20s.

High-Efficiency Compressor and Turbine Aerodynamics

BorgWarner uses their own proprietary CeraMet ceramic ball bearing cartridge and dual-lip piston ring seals in the EFR series. The 6758's compressor map shows a wide efficiency island, meaning the turbo produces high airflow with minimal temperature rise across a broad RPM range. Combined with the low-inertia turbine wheel, this results in very quick spool—often reaching full boost by 3500 RPM on a properly configured FA20.

Cost-Effective Path to Significant Power

While complete turbo kits from companies like Full-Race or Crawford Performance can cost $4,000–$6,000, a standalone BorgWarner EFR 6758 can be purchased for roughly $1,200–$1,500. By sourcing individual components (manifold, downpipe, intercooler, oil lines) or adapting existing parts, a budget-minded builder can assemble a complete turbo system for under $3,000—a fraction of the cost of a large-frame turbo setup.

Installation Process: A Realistic Guide

Installing the BorgWarner EFR 6758 on a Subaru FA20 demands intermediate mechanical skills and a solid understanding of turbocharger systems. The process is not for beginners, but with careful planning and the right tools, a home garage installation is achievable. Below is an expanded walkthrough.

Phase 1: Preparation and Parts Assessment

Before touching the car, gather all necessary components. The EFR 6758 itself requires a custom or adapted exhaust manifold (the FA20's stock header is not designed for a turbo location). Many builders use a top-mount or equal-length "triangle" manifold fabricated by shops like M&S Performance or JDL Auto Design. You will also need:

  • Custom downpipe with 3-inch outlet
  • Front-mount intercooler (FMIC) kit or a top-mount upgrade (TMIC) if staying low-boost
  • Oil feed and return lines with proper AN fittings
  • Vacuum lines for boost control and bypass valve
  • Intake pipe with appropriate MAF sensor housing
  • Aftermarket engine management (ECU reflash or standalone like ECUtek or Haltech)
  • Upgraded fuel pump (e.g., AEM 340LPH) and injectors (minimum 550cc, ideally 700cc)

Do not attempt the installation without a plan for fuel delivery and tuning—more on that in the tuning section.

Phase 2: Removing the Stock System

Disconnect the battery and drain the coolant. Remove the stock intake manifold, downpipe, and exhaust manifold. The FA20's boxer layout makes the driver's side manifold accessible, but you will need to unbolt the engine undercover and possibly lift the engine slightly for clearance. Remove the factory oil cooler and adapt fittings for the new oil supply line. Label all connectors and hoses as you go; reassembly is far easier with a reference.

Phase 3: Installing the EFR 6758 and Support Hardware

Mount the turbo manifold first, using new gaskets and torque-to-yield fasteners (30 ft-lbs for most flanges). Position the EFR 6758 on the manifold with the supplied gasket. Attach the oil feed line to the top of the turbo bearing housing and the oil return line to the bottom. For the coolant lines, many builders use a simplified system; BorgWarner recommends flowing coolant through the center housing to prevent coking after shutdown.

Run the intercooler piping. A FMIC kit for the FA20 typically routes piping along the passenger side, through the factory fog light area. Secure all couplers with T-bolt clamps. Install the blow-off valve (EFR's integrated unit can be recirculated or vented to atmosphere depending on your MAF setup).

Phase 4: Reassembly and Initial Checks

Reconnect the intake pipe and MAF sensor. Reattach the downpipe using a new gasket. Fill the engine with fresh oil and coolant. Before starting, disconnect the fuel pump relay and crank the engine for 10 seconds to prime the oil system. Reconnect the relay and start the engine. Let it idle and check for oil leaks, coolant leaks, and exhaust leaks. Bleed coolant as needed.

Tuning the Subaru FA20 for the EFR 6758

Tuning is the most critical aspect of a turbo upgrade. The FA20's direct injection (DI) system is sensitive to boost pressure and knock. Without proper calibration, detonation can destroy pistons within minutes. Here is a detailed approach to tuning.

Fuel System Requirements

The stock FA20 fuel injectors and in-tank pump are barely adequate for naturally aspirated operation. With boost, you must upgrade the pump and injectors. A 340LPH pump is the minimum for 300 whp; many tuners recommend a surge tank or fuel pump controller for reliability. Injectors should be 550cc for 250–300 whp, but 700cc is safer for a 300–350 whp setup. The DI injectors themselves can be a limitation; some tuners add port injection or run eFlex (flex fuel) to increase octane and cooling.

Boost Strategy and Wastegate Control

Start with a conservative spring pressure (e.g., 7–8 PSI) in the EFR's internal wastegate actuator. This gives a safe baseline to evaluate AFR and knock margin. Use a boost controller (electronic or manual) to increase boost gradually in 1–2 PSI increments. The EFR 6758 can comfortably deliver 15–18 PSI on 93 octane, and 20–22 PSI with ethanol fuel (E85). However, the FA20's weak point is the ringlands; many stock engines have failed at over 18 PSI. Support with a proper intercooler is non-negotiable.

Ignition Timing and Air-Fuel Ratio

Use a wideband oxygen sensor and a logged knock detection system (factory knock sensor or aftermarket like an accessport). Target an AFR of 11.5–11.8:1 under full boost on gasoline, and 12.0–12.5:1 on E85. Ignition timing should be conservative in the mid-range (10–15 degrees) and advanced only after verifying no knock. Many experienced FA20 tuners use a "torque-based" strategy with ECUtek software to manage load.

Monitoring and Safety

Install a boost gauge, wideband AFR gauge, and oil temperature gauge. Log regularly during tuning sessions. Watch for fuel pressure drop at high RPM—if the pump cannot supply enough pressure, the mixture will lean dangerously. If you notice knock at part throttle, reduce timing or increase enrichment. Never tune on the street without a safety map; use a dyno for final calibration.

Expected Results: Real-World Power and Driving Feel

After installation and proper tuning, the BorgWarner EFR 6758 transforms the FA20's character. Here are typical results based on community data and dyno sheets from shops like MotoEast and Don't Like Dirt Rac.

Power Output

On 93 octane with 14–15 PSI boost, an FA20 with the EFR 6758 and proper supporting mods (FMIC, 700cc injectors, pump, exhaust) regularly produces 280–310 whp and 270–290 lb-ft of torque. Compared to the stock 160 whp (on a Dynojet), that's a gain of 120–150 wheel horsepower. On E85 with 18–20 PSI, outputs of 340–370 whp and 330–350 lb-ft are common. Some aggressive setups have reached over 400 whp, but those require built internals (rods and pistons) and upgraded head studs.

Drivability and Turbo Lag

The EFR 6758 spools remarkably quickly on the FA20's 2.0L displacement. Boost threshold begins around 2800 RPM, with full boost by 3500 RPM. This is only slightly slower than the stock FA20's torque peak. The result is a linear, responsive powerband that feels like a large-displacement naturally aspirated engine. There is no dramatic "power hit" – the car simply pulls harder from 3000 RPM to redline (7500 RPM). The integrated bypass valve eliminates surge during gear changes.

Sound and Driving Emotion

The EFR turbo adds a distinct "diverter valve" sound and a crisp whistle on acceleration. The boxer engine's exhaust note becomes deeper and more aggressive. Many owners report the car feels "alive" with the turbo fitted—the slight increase in intake noise and boost reference makes every drive an event.

Common Pitfalls and Reliability Considerations

No budget turbo upgrade comes without trade-offs. The FA20's direct injection system can lead to carbon buildup on intake valves after high mileage, which reduces performance. With the increased heat from boost, this issue can accelerate. Consider periodic walnut blast cleaning or an oil catch can to reduce deposits.

Another common issue is oil starvation during sustained high-RPM cornering (autocross or track days) due to the FA20's oil pan design. An aftermarket oil baffle or a larger capacity pan is recommended for any forced induction track use. Additionally, the stock FA20 clutch will often start slipping above 280 ft-lb of torque; budget for a stage 2 or stage 3 clutch (e.g., ACT, Exedy).

Finally, the EFR 6758's internal wastegate actuator can sometimes creep boost higher than desired if the exhaust backpressure is high. Ensure the downpipe is properly sized (3-inch, mandrel-bent) and that the wastegate port is not obstructed by the manifold.

External Resources for Further Learning

Final Thoughts: Is the EFR 6758 Right for You?

The BorgWarner EFR 6758 turbo offers an excellent balance of cost, performance, and driveability for the Subaru FA20 engine. It is not a "cheap" solution—you still need quality components, fueling upgrades, and professional tuning—but it is far more affordable than off-the-shelf turbo kits while delivering comparable results. For the enthusiast willing to do the fabrication and tuning homework, the EFR 6758 can turn your FA20 into a responsive, 300+ horsepower machine that retains its daily usability and charm. Approach the project with patience, invest in proper monitoring equipment, and respect the engine's limitations, and you will have a rewarding turbocharged Subaru experience.