Understanding Superchargers and the FA20 Engine

A supercharger forces compressed air into the engine, allowing more fuel to be burned and producing greater power. For the Subaru BRZ, which uses the naturally aspirated FA20 boxer engine, a supercharger is a popular upgrade to address the car’s modest factory output. The FA20 is a 2.0-liter four-cylinder engine with a high compression ratio (12.5:1 in the BRZ) and direct injection. Its design prioritizes efficiency and response, but it can handle moderate forced induction with proper supporting modifications.

How a Supercharger Works

Unlike turbochargers that rely on exhaust gas flow, superchargers are mechanically driven by the engine’s crankshaft via a belt. This provides instant boost with no lag, making them ideal for drivers who want immediate throttle response. The two main types used on the BRZ are centrifugal and twin-screw (positive displacement). Centrifugal units behave like a belt-driven turbo, building boost as RPM climbs, while twin-screw units deliver consistent boost across the rev range, often giving a more aggressive low-end torque increase.

The FA20’s Strengths and Weaknesses

The FA20 is a robust engine with a forged steel crankshaft and connecting rods, but it uses cast aluminum pistons. Its direct injection system provides excellent fuel atomization, but at higher boost levels the stock fuel system can become a limiting factor. The compression ratio is high for forced induction, so boost levels must be carefully managed to avoid detonation. A 9 PSI supercharger sits within the safe operating window for the FA20 when paired with proper fuel and cooling upgrades.

Why 9 PSI? The Sweet Spot for the BRZ

9 PSI of boost from a supercharger represents a well-documented power increase that respects the FA20’s mechanical limits. This boost level typically yields 250–280 wheel horsepower (whp) on a properly tuned BRZ, up from the stock 180–190 whp. The gain in torque is equally impressive, with peak torque arriving lower in the rev range, dramatically improving everyday drivability without sacrificing reliability.

Safe Boost Threshold

The FA20’s factory engine management and fuel system can handle short bursts of boost, but sustained 9 PSI requires a tune. At 9 PSI, the stock internals—especially the cast pistons and rod bearings—are under increased load, but remain within design tolerances if detonation is avoided through proper calibration and fuel quality. Higher boost levels (12+ PSI) often necessitate forged pistons, oil coolers, and upgraded fuel components. 9 PSI is considered the “no internal engine work” threshold for many kits.

Power Expectations

Typical dyno results for a 9 PSI supercharged BRZ range from 240–270 whp on a Dynojet, with torque around 210–240 lb-ft. This transforms the car from a slow-but-fun coupe into a legitimate sports car that can keep pace with much more expensive machinery. The powerband remains linear, especially with centrifugal superchargers, making the car predictable and rewarding on track or back roads.

Component Upgrades for a 9 PSI Kit

Installing a supercharger is not a standalone modification. To achieve reliable and consistent performance, additional supporting components are necessary.

Fuel System Requirements

At 9 PSI, the stock direct injectors and fuel pump can run out of capacity at high RPM, leading to lean conditions and potential engine damage. Most supercharger kits include or recommend upgraded injectors (often supplemental port injectors) and a higher-flow fuel pump. A common solution is a returnless fuel system with a boost-referenced regulator, or a flex-fuel setup if E85 is available. Always upgrade the fuel system before or during the supercharger installation.

Cooling Systems

Forced induction increases intake air temperatures, which can cause detonation. A good intercooler (air-to-air or air-to-water) is included in most 9 PSI kits. Additionally, an oil cooler is strongly recommended for track use, as the FA20 already runs hot under load. A larger radiator and upgraded engine oil cooler help maintain consistent temperatures during sustained high-RPM driving.

Tuning Solutions

The engine control unit (ECU) must be recalibrated to adjust fuel and ignition timing for the forced induction setup. Options include reflashing the factory ECU via software like EcuTek, or installing a standalone ECU such as a Haltech or Motec. EcuTek is the most popular choice for BRZ supercharger kits because it retains the factory cold-start, cruise, and emissions strategies. A reputable tuner with FA20 experience is essential—a bad tune can destroy the engine in minutes.

Selecting the Right Supercharger Kit

Several manufacturers produce 9 PSI supercharger kits for the BRZ. The choice depends on driving preferences, budget, and intended use.

Centrifugal vs. Twin-Screw/Roots

  • Centrifugal (e.g., Jackson Racing, Vortech): Smooth, progressive power delivery. Boost builds with RPM, mimicking a larger naturally aspirated engine. Excellent for track use because it doesn’t tax the cooling system as much at low RPM. Generally easier on the drivetrain.
  • Twin-Screw/Roots (e.g., Harrop, Edelbrock): Immediate, strong low-end torque and peak boost early. Gives a more aggressive feel but can stress the tires and transmission. Produces more heat due to the internal compression, requiring robust cooling.
  • Jackson Racing C38-91 Kit: A centrifugal supercharger that delivers 9–10 PSI with a CARB EO street-legal tune. Includes an air-to-oil oil cooler, upgraded injectors, and a reflash. Known for its reliability and smooth power.
  • Harrop TVS1320 Kit: A twin-screw positive displacement unit that provides strong low-end torque. Comes with an air-to-water intercooler and a CARB-legal tune. Excellent for street driving and autocross.
  • Edelbrock E-Force Kit: A Roots-type supercharger with an integrated water-to-air intercooler. CARB approved, and known for its OEM-like fit and finish.
  • Vortech V3 Si-Trim: A centrifugal kit often paired with a custom tune. More affordable but requires more installation effort and tuning support.

For more details, check the Jackson Racing website for their BRZ supercharger offerings.

Installation Walkthrough (Expanded)

Installing a 9 PSI supercharger is a multi-day project for a home mechanic or a one- to two-day job at a professional shop. The following steps are a general guide; always refer to the specific kit’s instruction manual.

Preparation and Tool List

Gather the entire supercharger kit, including all brackets, belts, pulleys, hoses, and hardware. You will need standard hand tools (socket set, wrenches, screwdrivers), a torque wrench, a coolant vacuum filler (to avoid air pockets), a scan tool for ECU flashing, and fluids (engine oil, coolant, supercharger oil if applicable). Disconnect the battery before starting work.

Step-by-Step

  1. Drain coolant and remove the intake system. Disconnect the stock airbox, intake tube, and MAF sensor. Drain the engine coolant because the supercharger may interfere with the water pump or require hose modifications.
  2. Remove the intake manifold. Disconnect the fuel injectors, manifold bolts, and any vacuum lines. Clean the intake ports and replace gaskets.
  3. Install the supercharger mounting bracket. This attaches to the engine block or cylinder head. Torque bolts to spec. Some kits require removing the alternator or power steering pump for access.
  4. Mount the supercharger unit. Slide the supercharger onto the bracket and secure it with included bolts. Install the drive belt and tensioner according to instructions.
  5. Attach intercooler and charge piping. Most kits include an air-to-air intercooler that mounts in front of the radiator, or an air-to-water unit that uses a separate heat exchanger. Route hoses to the throttle body and supercharger outlet.
  6. Reassemble the intake system. Reinstall the intake manifold, now with new fuel injectors (if supplied). Connect the recirculation valve or bypass valve for the supercharger.
  7. Finish coolant and electrical connections. Refill coolant, install larger radiator if applicable, and connect any boost-pressure sensors or fuel pump controllers provided with the kit.
  8. Check for leaks. Before starting, double-check all vacuum hoses, clamps, and the belt tension. Prime the oil system if the supercharger has its own oil supply.
  9. Tune the ECU. Load the base calibration from the kit manufacturer or your tuner. Perform a cold start and let the engine idle until warm. Check for any abnormal noises or leaks.
  10. Road test and data log. Gradually increase load while monitoring air/fuel ratio, knock correction, and boost pressure. Make adjustments as needed.

Tuning and First Start

Never start the engine without a proper tune. Use a flashing tool like EcuTek or OpenFlash tablet. For safety, set the traction control to full-off during initial tuning to avoid interference. Have a fire extinguisher handy. After a successful first start, perform a gentle break-in drive of 50–100 miles on low boost before attempting full-throttle runs.

Post-Installation Maintenance and Longevity

A supercharged BRZ requires more attentive maintenance than a stock car, but a 9 PSI setup can be reliable for many miles if cared for.

Oil and Fluid Changes

Change the engine oil every 3,000–4,000 miles using a high-quality 5W-30 full synthetic with good wear protection. The supercharger’s oil (usually a specific gear oil or synthetic fluid) should be checked and replaced per the manufacturer’s schedule—typically every 15,000–30,000 miles. Coolant should be flushed every 2 years, and the intercooler system (if water-to-air) should be refreshed with distilled water and coolant additive.

Belt Inspection and Tensioning

The supercharger drive belt experiences high tension. Inspect it monthly for cracks, glazing, or wear. Replace at the first sign of damage. Keep the proper belt tension—over-tightening can damage bearings, while a loose belt can slip and reduce boost. Many kits use an automatic tensioner; if manual, check the tension at every oil change.

Monitoring Knock and AFR

Invest in a wideband air/fuel ratio gauge and a knock sensor display (or use your tuning software’s data logging). The FA20 is particularly sensitive to knock. If you hear pinging or see knock counts on the ECU log, cease aggressive driving and have the tune adjusted. Using high-octane fuel (91 AKI or higher) is mandatory; E85 provides excellent knock resistance and often allows more timing advance for increased power.

Cost Analysis

Budgeting for a 9 PSI supercharger upgrade goes beyond the kit price.

Kit Cost

A complete supercharger kit for the BRZ ranges from $4,500 to $6,500, depending on the brand and included components. Kits with integrated oil coolers and injectors cost more upfront but simplify installation.

Installation Labor

Professional installation typically runs $1,000 to $2,000, depending on the shop rate and whether additional work (e.g., fuel system upgrade, tuning) is included. DIY installation saves labor but requires several days and proper tools.

Additional Mods and Tuning

  • Fuel system upgrades: $500–$1,200 (injectors, pump, regulator)
  • Oil cooler: $300–$600
  • Radiator upgrade: $300–$800
  • Tuning: $500–$1,500 for EcuTek license and custom tune
  • Miscellaneous (belts, fluids, gaskets): $100–$200

Total all-in cost: $7,000 to $12,000, making it a significant investment but one that transforms the car.

Frequently Asked Questions

Can I run 9 PSI without an intercooler?

No. Intake air temperatures will skyrocket, causing knock and likely engine damage. All reputable 9 PSI kits include an intercooler.

Will a 9 PSI supercharger void my warranty?

Yes, most manufacturers will deny powertrain claims if a supercharger is detected. Some aftermarket warranties may still cover the car, but read the fine print. For a newer BRZ, consider a used car or one that is out of warranty before modifying.

How much horsepower can I expect with a 9 PSI supercharger on 93 octane?

Typically 250–270 whp with a safe tune. On E85, gains of 280–300 whp are possible with proper fueling.

Is the stock clutch ok for 9 PSI?

The stock BRZ clutch can handle the increased torque for a while, but it may slip under aggressive driving. Many owners upgrade to a stage 1 or stage 2 clutch (e.g., Exedy, ACT) for peace of mind.

Conclusion

Upgrading to a 9 PSI supercharger on your Subaru BRZ is one of the most rewarding modifications you can make. It elevates the car from a momentum machine to a serious performer while retaining the handling and balance that make the BRZ special. With the right kit, supporting modifications, and a quality tune, a 9 PSI setup can be both reliable and exhilarating. Research your options, budget for all necessary upgrades, and work with experienced professionals. For additional real-world owner experiences, visit forums like FT86 Club’s Forced Induction section to learn from those who have already made the jump.