The $5,500 FA20 Performance Blueprint

Building a reliable, high-horsepower FA20 engine for the Subaru BRZ or Toyota 86 requires a strategic plan and strict budget adherence. The FA20 is a capable platform, but its high 12.5:1 compression ratio and fragile connecting rods demand a specific upgrade path for forced induction. This combination features Cosworth forged pistons and a Garrett GTX2860R Gen II turbocharger, targeting a total build cost of $5,500. Achieving 300 to 350 wheel horsepower on a reliable, daily-driven engine is the goal, and every dollar in this breakdown is allocated to reach that target without cutting corners on durability.

The FA20 Platform – Strengths and Weaknesses

The FA20D engine found in the Subaru BRZ, Scion FR-S, and Toyota 86 is a 2.0-liter flat-four that produces roughly 200 horsepower at the crank. It features a unique D-4S injection system that combines direct injection with port injection. This allows for excellent fuel atomization and high compression, but it also introduces specific challenges. The direct injection system is prone to carbon buildup on the intake valves because there is no fuel washing over them. The high compression ratio, while great for fuel economy, creates a high cylinder pressure environment that is hostile to forced induction.

The stock connecting rods and pistons are the primary weak points when adding boost. The rod bolts stretch easily under increased cylinder pressure, and the hypereutectic pistons are brittle. Extensive documentation on platforms like FT86 Club shows that exceeding 300 wheel horsepower on the stock short block is a gamble. For a build targeting 300-350 wheel horsepower, replacing the pistons and rods with forged components is mandatory for long-term reliability. The closed-deck block design of the FA20 is strong, but the internal reciprocating assembly must be upgraded to handle the stress of a turbocharger.

Core Components: Cosworth and Garrett

Why Cosworth Forged Pistons?

Cosworth is a motorsport original equipment manufacturer (OEM) with decades of experience in Formula One and rally applications. Their piston for the FA20 is machined from 2618-T6 aluminum alloy, a material known for its high fatigue strength and ability to withstand extreme thermal loads. This is a critical distinction from cheaper 4032 alloy pistons, which are harder but more brittle under high boost conditions. The 2618 alloy expands more, requiring careful piston-to-wall clearance, but it offers superior durability when the engine is pushed hard.

The specific ring pack on the Cosworth pistons is designed to handle the thermal load of a forced-induction FA20. The top ring is placed lower on the piston crown to reduce heat transfer, and the ring end gaps are engineered for boost. While cheaper piston options exist from brands like Wiseco or JE, the consistency of the forging process and the longevity of Cosworth pistons justify the $1,200 investment. They are a "drop-in" fit for the FA20 block, meaning no major modification is required, but proper machining for clearance is essential.

Garrett GTX2860R Gen II – The Ideal Turbo

Selecting the correct turbocharger is critical for a street-driven FA20. The Garrett GTX2860R Gen II is the optimal match for a 2.0-liter engine aiming for 300-350 wheel horsepower. It features a 52.5mm inducer wheel and a 60mm exducer wheel on the compressor side, paired with a 54mm turbine wheel in a 0.64 A/R housing. The dual ball bearing core reduces friction and allows the turbo to spool incredibly quickly.

As detailed on Garrett Motion's official page, the Gen II series features an upgraded compressor aerodynamics package that improves efficiency by 5-7% compared to the original GTX2860R. This means the turbo reaches full boost by 3,500 RPM on a 2.0L engine, providing a torque curve that feels like a naturally aspirated engine with significantly more displacement. The response is immediate, making it a joy to drive on the street and on track. Compared to a larger frame turbo like a GT3071R, the GTX2860R sacrifices some top-end peak power for a much wider, flatter torque curve.

Comprehensive $5,500 Budget Breakdown

Here is exactly how the $5,500 budget is allocated to ensure a reliable and complete FA20 build. Each line item is chosen to maximize performance without sacrificing the longevity of the engine.

1. Cosworth Pistons ($1,200)

  • Piston Set: Includes pins, rings, and lock rings. Select a 9.5:1 compression ratio for forced induction.
  • Machining: Budget $400 for bore/hone and decking. A torque plate is essential for accurate honing.

2. Garrett Turbocharger ($1,500)

  • Turbo Core: Garrett GTX2860R Gen II.
  • Kit Components: A quality turbo kit (manifold, downpipe, intake, intercooler) is an additional cost that must be absorbed into the budget or built piece by piece.

3. Upgraded Fuel System ($800)

  • Injectors & Pump: A set of 700cc port injectors or a direct injection upgrade, paired with an AEM 340lph or equivalent fuel pump.
  • Flex Fuel: Budget permitting, an ethanol content sensor and flex fuel kit will unlock the true potential of the build.

4. ECU Tune & Software ($500)

  • ECUTEK License & Cable: $500. This is the mandatory entry point for professional tuning on the FA20.

5. Exhaust System ($600)

  • Cat-Back Exhaust: $600. A 3-inch mandrel bent system reduces backpressure.
  • Front Pipe: Often included in turbo kit. If not, budget a high-flow unit to replace the restrictive factory cat.

6. Labor & Assembly ($900)

  • Short Block Assembly: $500. Machine shop labor to install pistons/rods and close the block.
  • Turbo Kit Installation: $400. A skilled flat-rate technician can complete this in a weekend.

7. Miscellaneous Parts & Consumables ($500)

  • Gaskets & Seals: Full engine gasket set.
  • ARP Hardware: Head studs, main studs.
  • Fluids: Engine oil, coolant.

Total Estimated Cost: $5,500

This breakdown assumes a balance of new and used components. A diligent shopper can find deals to stay within this budget without sacrificing quality.

Critical Machining and Assembly Steps

Installing Cosworth pistons requires meticulous machine work. The FA20's closed-deck block must be honed to the exact cross-hatch pattern and clearance.

Piston-to-Wall Clearance

Forged pistons expand more than hypereutectic cast pistons. The machine shop must provide the correct clearance... typically 0.0035" to 0.0040"...

Ring Gap Filing

Boost adds immense heat to the top ring... The top ring gap must be filed to... 0.022" for a forced induction application...

Tuning the Combination for Reliability and Power

A build is only as good as its tune... The FA20 is notoriously sensitive to knock... Using ECUTEK Race Rom... A reputable tuner...

Flex fuel is a game changer for the FA20... E85 cools the combustion chamber... allowing for significant timing advance...

Realistic Power Output and Driveability

With the Cosworth pistons, Garrett turbo, and a proper tune, a 300-350 whp FA20 is a reliable street machine... The spool characteristics of the GTX2860R... The torque curve... flat and wide...

Final Verdict

The $5,500 budget is tight but achievable. It forces smart choices: Cosworth for proven reliability, Garrett for efficient power, and a focus on essential supporting modifications. Skimping on the ECU tune or fuel system will compromise the build. A strict adherence to the plan and realistic power expectations (300 whp) will result in a highly enjoyable, reliable FA20 build.