Understanding the FA20 Engine and Its Limitations

The Subaru FA20 is a 2.0-liter, naturally aspirated flat-four engine that powers the Subaru BRZ, Scion FR-S, and Toyota 86. Its horizontally opposed design delivers a low center of gravity, which gives these cars sharp handling characteristics right from the factory. Out of the box, the FA20 produces about 200 horsepower and 151 lb-ft of torque—respectable numbers for a lightweight sports car. However, the engine is designed for efficiency as much as performance, and its internals are built to meet standard reliability targets at stock power levels.

When enthusiasts push beyond bolt-on modifications like headers, exhaust, and intake, the stock FA20 internal components quickly become limiting. The cast pistons and rods are not designed to withstand sustained high-RPM operation or the added stress of forced induction. Even with aggressive cam tuning on a naturally aspirated setup, the factory valvetrain can exhibit instability above 7,500 RPM. Recognizing these constraints is the first step toward a build that maximizes power without sacrificing reliability.

Why Upgrade Internals on a Budget

Upgrading the FA20 internals for under $2,000 is a realistic goal if you focus on the parts that provide the most significant performance gains. Rather than replacing every component, smart budget allocation allows you to strengthen the rotating assembly and valvetrain where it matters most. Many high-performance builds on platforms like the FT86 Club forum document builds that achieve over 300 wheel horsepower on a fully built bottom end—using only a modest investment in forged internals and proper tuning.

The benefits of upgrading internals go beyond raw horsepower. Forged pistons and rods improve heat dissipation, reduce the risk of detonation, and allow you to raise the redline safely. Upgraded valve springs prevent valve float at high RPM, enabling cam profiles that deliver more mid-range and top-end power. The result is an engine that not only makes more power but also responds better to tuning and delivers a linear, thrilling power curve.

Core Benefits at a Glance

  • Increased horsepower and torque: Forged internals allow higher cylinder pressures and more aggressive timing. Gains of 30–50 horsepower on a naturally aspirated build are common, and forced induction setups can exceed 400 horsepower without the fear of rod failure.
  • Improved reliability under stress: Factory rods are prone to bending under sustained boost or high-RPM use. Upgrading to forged H-beam or I-beam rods eliminates this weak point.
  • Higher RPM capability: With stronger rods and upgraded valvetrain, you can safely rev to 8,000 RPM or more, accessing additional power that stock internals would never survive.
  • Better thermal management: Forged pistons dissipate heat more effectively than cast units, reducing the chance of hot spots and pre-ignition.

Key Internal Upgrades Under $2,000

Building a reliable, high-performance FA20 on a budget requires choosing components that offer the best return on investment. Below are the most impactful upgrades, along with advice on prioritizing them for your specific goals.

Pistons

High-compression forged pistons are a staple of naturally aspirated builds, while lower-compression versions are ideal for turbocharging or supercharging. Expect to spend between $500 and $800 for a set of four pistons from brands like Manley or CP-Carrillo. Look for pistons with a robust ring pack and an anti-friction coating. For a budget build, aim for a compression ratio around 11.5:1 if staying naturally aspirated, or 9.5:1 if you plan to add forced induction later.

Connecting Rods

Forged connecting rods are arguably the most critical upgrade for any FA20 build that will see track time or boost. Stock rods are cast and are a known failure point at power levels above 300 wheel horsepower. H-beam or I-beam rods from manufacturers like Eagle or K1 Technologies cost between $400 and $600 and provide a significant safety margin. They also reduce reciprocating mass, which helps the engine rev more freely.

Camshafts

Performance camshafts optimize valve timing to improve volumetric efficiency throughout the RPM range. A set of stage 2 or stage 3 camshafts for the FA20 costs $300 to $500. They shift the power band higher, which pairs well with a raised rev limit. When combined with upgraded valvetrain components, they can unlock an additional 15–25 horsepower on an otherwise stock engine.

Valves, Springs, and Retainers

To take full advantage of aggressive camshafts, you need valve springs that prevent float at high RPM. A complete valvetrain upgrade—including springs, retainers, and titanium keepers—costs $250 to $400. Some budget builds reuse stock valves if they are in good shape, but upgrading the springs is non-negotiable for any build that will exceed 7,500 RPM.

Optional Upgrades: Bearings and Oil Pump

If your budget allows, replacing the main and rod bearings with high-performance versions (around $100–$200) adds an extra layer of durability. Similarly, an upgraded oil pump ($200–$300) ensures consistent oil pressure at elevated RPM. While these are not strictly essential for the first $2,000, they are highly recommended if you plan to track the car or run forced induction in the future.

Cost Breakdown Summary

The following table represents a realistic allocation for a $2,000 internal upgrade budget, assuming you perform the labor yourself. Prices are estimates based on current retail pricing from reputable suppliers.

  • Pistons (forged set): $600
  • Connecting rods (forged H-beam): $500
  • Camshafts (stage 2): $400
  • Valve springs and retainers: $350
  • Gasket set and fasteners: $150
  • Total: $2,000 (before contingency)

If you need professional installation, budget an additional $500–$800 for labor, which may require you to drop the camshaft or valve spring upgrades initially and add them later. Alternatively, you can prioritize pistons and rods first, then save for camshafts as a second phase.

DIY vs. Professional Installation

Rebuilding an FA20 is not for the faint of heart. It requires specialized tools (torque wrench, ring compressor, valve spring compressor, engine lift) and a clean workspace. The factory service manual for the Subaru BRZ is essential reading. DIY can save $500 or more, but mistakes—such as improper ring gap or incorrect bearing clearance—can lead to catastrophic engine failure. If you have experience building four-cylinder engines and own the necessary tools, DIY is a rewarding and cost-effective route.

Professional installation gives you peace of mind and typically includes a warranty on labor. Shops that specialize in Subaru or Toyota engine builds, such as IAG Performance, understand the specific requirements of the FA20. The extra cost is often worth it if this is your first engine build or if you are on a tight timeline.

Potential Risks and Considerations

Engine Management Tuning

After any internal upgrade, the engine management system must be recalibrated. The stock ECU uses narrow-band oxygen sensors and advanced fuel trims that will not adapt to new piston compression or cam timing. You will need a custom tune via a platform like ECUTek or OpenFlash Tablet. Budget $400–$600 for professional tuning. Failure to tune the engine can result in detonation, excessive timing advance, and serious internal damage.

Reliability at the Limit

Stronger internals do not guarantee long engine life if other supporting systems are neglected. Oil temperature, fuel delivery, and cooling all become critical when power output increases. Install an oil cooler if you plan to track the vehicle, and consider a catch can to mitigate oil ingestion. The FA20 is particularly sensitive to oil starvation during sustained high-G corners; a baffled oil pan or Accusump can prevent bearing failure.

Warranty and Emissions

Internal modifications void any remaining factory powertrain warranty. Additionally, aftermarket camshafts may not pass smog testing in some regions. Check local regulations before proceeding. In many cases, a turbo or supercharger kit combined with stock internals is a more straightforward path to power, but it carries its own risks and costs above $2,000.

Alternative Approaches Within the Budget

If your ultimate goal is forced induction, you might consider starting with only forged pistons and rods, then saving for a turbo kit later. This allows you to allocate the full $2,000 to the bottom end alone. Alternatively, a naturally aspirated build with pistons and cams can yield a satisfying 220–240 wheel horsepower without the complexity of forced induction. The key is to align your upgrade path with your final power target and driving use.

Conclusion

Upgrading the FA20 internals for under $2,000 is not only possible but also a proven strategy for building a reliable, high-performance engine. By focusing on forged pistons, connecting rods, and a matching valvetrain, you can safely increase power, rev higher, and improve overall durability. Careful planning, diligent research, and proper tuning are essential to realizing the full potential of your investment. Whether you choose to tackle the build yourself or hire a professional, the result will be a more responsive and exciting driving experience that justifies every dollar spent.