Understanding the FA20 Engine Platform

The Subaru BRZ and its sibling the Toyota 86 share the FA20, a 2.0-liter naturally aspirated flat-four engine that prioritizes balance and response over outright power. Its boxer layout keeps the center of gravity low, contributing to the car's legendary handling. The engine uses a dual-injection system combining direct injection with port injection, which helps manage carbon buildup on intake valves while delivering precise fuel metering. Factory output sits at approximately 200 horsepower and 151 lb-ft of torque. While the FA20 is willing to rev, its torque curve is relatively flat, and the engine responds well to airflow improvements and timing adjustments. Knowing these characteristics is essential before selecting parts that work with the engine's strengths.

Cold Air Intake Systems: Improving Induction Flow

The stock intake system is designed for noise suppression and packaging efficiency. Replacing it with a high-flow cold air intake can reduce restriction and lower intake air temperatures. These gains are modest on a naturally aspirated FA20, typically adding 5 to 8 horsepower, but throttle response improves noticeably, especially with supporting mods. When choosing an intake, consider filter media quality, heat shielding, and whether the intake tube retains the factory mass airflow sensor housing diameter.

Top Intake Options for the BRZ FA20

  • AEM Cold Air Intake – Uses a dry-flow, washable filter and a sealed housing that draws air from below the bumper. The system maintains consistent air density even in stop-and-go traffic. Requires removal of the sound tube, which reduces cabin drone. Gains of 6-8 whp with a tune.
  • Injen SP Series Intake – Features a polished aluminum tube and a high-flow oiled filter. The design preserves the factory airbox location and includes a heat shield. Noted for increasing intake noise without being intrusive. Works well with aftermarket exhausts for a sporty sound profile.
  • COBB Tuning SF Intake – This intake uses a giant cone filter with an integrated heat shield. The tune-specific design suits owners planning to use COBB's Accessport. Pre-loaded maps are calibrated for this intake, making it the most seamless choice for a staged upgrade path.
  • Perrin Cold Air Intake – Uses a hydrophobic cotton filter that resists water ingestion. The intake tube is mandrel-bent for smooth airflow. Includes a full aluminum heat shield and silicone couplers. Designed to spool forced induction systems more responsively if you later add a supercharger.

Installation Tips

Installation is straightforward for most DIY owners, taking about 45 minutes. Disconnect the battery before starting. Remove the factory airbox and sound tube. Clean the MAF sensor carefully if any oil residue transfers from the filter. Use only a light coating of oil on reusable filters to prevent contamination. Reset the ECU after installation by disconnecting the battery for at least 10 minutes. A tune is not strictly required for a cold air intake on the FA20, but a tune will extract the full benefit and prevent lean conditions at wide-open throttle.

Exhaust System Upgrades: Reducing Back Pressure

The FA20 engine produces exhaust pulses that benefit from a freer-flowing exit path. Restrictive factory components, including the mid-pipe resonator and muffler, create back pressure that reduces volumetric efficiency. Replacing sections of the exhaust from the header-back can improve scavenging and mid-range torque. The gains depend on which section you upgrade and whether you retain the catalytic converters.

Exhaust Component Options

  • Nameless Performance Axleback Exhaust – Replaces the mufflers with straight-through resonators. Offers multiple tip options and removable silencers. Provides a noticeable weight reduction of about 12 pounds. Produces a deep, refined tone without excessive drone at highway speeds. Gains of 3-5 whp with no check engine light.
  • GReddy Supreme SP Exhaust – A cat-back system with polished stainless steel construction and a large-diameter pipe. Uses a straight-through muffler design that balances sound output with interior comfort. Rated for about 5-7 whp gain. The quality of the welds and flanges makes installation straightforward.
  • Perrin Motorsport Exhaust – A resonator delete paired with a dual-exit muffler. Reduces weight by approximately 9 pounds compared to stock. The system is tuned to avoid drone in the 2500-3500 rpm range. Produces a sporty note at higher revs without being obnoxious at idle. Designed for maximum flow without losing all low-end torque.
  • Full Header-Back System – Combining an equal-length header, a high-flow cat (or test pipe), and a cat-back exhaust yields the largest gains, typically 12-18 whp. Tomei and Gruppe-S offer popular equal-length headers that change the exhaust note to a smoother, more refined sound. Expect a check engine light for the rear O2 sensor if you remove the secondary cat. A tune is required to clear the code and optimize fuel trims.

Choosing the Right Exhaust Profile

Consider your local noise regulations and your tolerance for cabin resonance. A full cat-back system with resonators is acceptable for daily driving, while a header-back setup with a test pipe may be too loud for some owners. If you plan to add forced induction later, a 2.5-inch or 3-inch diameter system is advisable to avoid needing a second exhaust purchase.

ECU Tuning: Unlocking the Full Potential

The factory ECU map on the FA20 is conservative, prioritizing emissions compliance and fuel economy. Spark timing is retarded in several load ranges, and the fuel mixture runs richer than necessary for peak power. Tuning the ECU addresses these compromises, often yielding 15-20 whp on an otherwise stock engine. When combined with intake and exhaust upgrades, a proper tune adds another 10-15 whp over the stock map by bringing the engine into an optimal air-fuel ratio and advancing ignition timing to the edge of knock.

ECU Tuning Solutions

  • ECUtek – Professional-grade tuning with support for multiple maps, launch control, flat-foot shifting, and flex fuel. Requires a certified tuner to license the software. Ideal for owners with heavily modified engines or those running ethanol blends. ECUtek provides datalogging capability to fine-tune parameters. The ProEcu Suite gives tuners access to every table in the ECU, including variable valve timing maps.
  • COBB Accessport – A handheld device that connects to the OBD-II port. Pre-loaded off-the-shelf (OTS) maps are available for stage 1 (stock), stage 2 (intake + exhaust), and stage 2+ (header). Maps are calibrated for specific parts like COBB's intake and exhaust. Users can switch maps in under a minute. The device also functions as a data monitor for boost, oil pressure, and engine temperature. Custom tuning is possible if you find a tuner who supports the COBB platform.
  • Open Flash Tablet – An affordable alternative to COBB Accessport. Offers pre-loaded maps for common bolt-ons and the ability to adjust parameters manually. Tunes are stored on the device and can be flashed back to stock easily. The open-source community provides a library of base maps for various configurations. Well-suited for owners who want fine control without paying for a professional tuning session.
  • Delicious Tuning Flex Fuel Kit – For owners considering E85, this kit includes an ethanol content sensor and remaps the ECU to adjust timing and fueling in real time. E85 offers a significant octane increase, allowing higher boost and more aggressive timing. Gains of 25-30 whp are common with E85 on a tuned FA20.

Important Tuning Considerations

The FA20 engine uses a knock control system that will pull timing if it detects knock events. A high-quality tune reduces false knock from normal engine noise, allowing the engine to maintain higher timing targets. Use 93 octane fuel (or 91 if that is the best available in your region) when running a performance tune. Ethanol blends require supporting mods, including larger fuel injectors or a low-pressure fuel pump, to maintain fuel delivery under load. Always perform a data log after installation to verify that the engine runs safely under all conditions.

Combining Upgrades for a Coherent Power Build

Individual upgrades provide incremental gains, but the real benefit comes from pairing components that work together. An intake alone may add 6 horsepower. An exhaust alone adds 5 to 8. An ECU tune adds 15. When you combine all three, the total is greater than the sum of the parts because the tune can take full advantage of the improved airflow.

  1. Start with a cold air intake. Install a high-flow intake system and run the car for a week to acclimate. This upgrade is reversible and requires no tune, though a tune is recommended for maximum benefit.
  2. Add a cat-back or axle-back exhaust. This will change the sound profile and slightly reduce back pressure. No tune is required for most cat-back systems, but the stock fuel trims will adapt within a few drive cycles.
  3. Install an equal-length header. This upgrade provides the largest single horsepower gain for a naturally aspirated FA20. Be prepared for a check engine light from the rear O2 sensor. Plan to either install a defouler or tune the ECU to clear the code.
  4. Flash the ECU. Use COBB Accessport, ECUtek, or Open Flash Tablet to apply a tune matched to your specific combination of parts. If you are running E85, ensure your fuel system can support it.
  5. Consider a flex fuel kit. E85 offers a substantial power increase (20-30 whp) and is a cost-effective upgrade compared to forced induction. Requires a flex fuel sensor and a tune that supports ethanol content.

Dyno Results and Real-World Gains

A common bolt-on BRZ with intake, header, exhaust, and a 93 octane tune will produce approximately 190-200 whp on a DynoJet. E85 with the same setup adds another 15-20 whp, bringing the total to 210-220 whp. This is a significant improvement over the stock baseline of 160-165 whp at the wheels. Keep in mind that forced induction remains the most effective way to exceed 250 whp, but a well-executed naturally aspirated build retains the responsive, high-revving character that makes the FA20 enjoyable.

Maintenance and Reliability After Upgrades

Upgrading your intake, exhaust, and tune does not drastically reduce engine lifespan if done properly. Stick to conservative timing and fuel mixtures. Monitor your oil temperature during hot track sessions and consider an oil cooler if you track the car frequently. The FA20 engine is known for issues with the valve spring recall on early 2013-2014 models, so confirm your car's status before pursuing high-performance builds. Regular oil changes with a high-quality 5W-30 synthetic oil are critical. The direct injection system on the FA20 can accumulate carbon on intake valves over time. A catch can system helps reduce this buildup and is a worthwhile addition to any modified FA20.

Frequently Asked Questions

Will an intake and exhaust void my new car warranty?

Modifications do not automatically void the entire warranty. The Magnuson-Moss Warranty Act in the United States protects consumers, placing the burden on the dealer to prove that a part caused a failure. An intake or exhaust alone is unlikely to cause engine failure, but a tune can be detected by the dealer during a scan. If you are concerned, keep your stock parts and re-install them before dealer visits.

Do I need a tune for just an intake?

A tune is not strictly required for an intake on the FA20 because the mass airflow sensor compensates for the increased airflow. However, a tune will let you realize the full power potential. Without a tune, expect only 2-3 whp from a cold air intake. With a tune, that increases to 5-8 whp.

What is the best first mod for the FA20?

A quality cat-back exhaust provides the most noticeable change in sound and driving feel for the investment. It is easy to install, reversible, and requires no tune. For those focused purely on power, an equal-length header combined with a tune is the best value for naturally aspirated builds.

Can I run E85 on a stock fuel system?

Yes, to a point. The stock fuel pump and injectors can handle E85 on a lightly modified naturally aspirated FA20. If you add forced induction or run E85 with a header and tune, upgrade to a larger low-pressure fuel pump and 700cc+ injectors to maintain fuel flow at high rpm.

Conclusion

Boosting FA20 power is a rewarding process that respects the engine's naturally aspirated character while delivering measurable performance improvements. Focus on high-flow intake and exhaust systems that improve volumetric efficiency, and pair them with a proper ECU tune to optimize fueling and timing. A bolt-on BRZ with intake, header, cat-back exhaust, and a 93 octane tune produces a lively, responsive powerband that makes the already excellent chassis even more engaging. For those willing to run E85, the gains are substantial enough to rival early-stage forced induction kits. Whichever path you choose, maintain your car meticulously and log your data to keep the engine running safely for many miles.

For more information on FA20 tuning communities and detailed build threads, the FT86 Club forums offer extensive real-world owner experiences. COBB Tuning's official site provides specifications and map notes for their Accessport, and ECUtek's dealer locator can connect you with a certified tuner near you.