The FA24 Engine: A Performance Foundation

The FA24 engine in the second-generation Subaru BRZ marks a significant step forward from its predecessor. This 2.4-liter naturally aspirated flat-four delivers 228 horsepower and 184 lb-ft of torque from the factory, representing gains of 23 horsepower and 28 lb-ft over the FA20. The additional displacement provides a broader torque curve and greater headroom for modification. Unlike turbocharged platforms, reaching 300 wheel horsepower on the FA24 requires careful part selection, attention to airflow, and precise calibration. With the right intake, exhaust, and tuning package, the NA configuration can deliver impressive output while maintaining daily driveability.

The FA24's built-in advantages include a robust closed-deck block design, adequate oiling for track use, and a variable valve timing system that responds well to aftermarket calibration. However, the factory intake and exhaust systems create bottlenecks that limit peak output. Addressing these restrictions is essential before tuning. This guide covers the proven intake and exhaust paths that community builders and professional tuners have validated for reaching the 300 HP threshold.

Intake Upgrades: Feeding the FA24

The factory air intake system on the BRZ FA24 prioritizes noise reduction and packaging over flow. The airbox, intake tube, and filter all introduce pressure drops that become more restrictive as RPM climbs. An aftermarket intake system reduces restriction and can lower intake air temperatures, which directly supports higher power output. The key is selecting a design that flows enough air for your target power level without increasing intake temperatures during sustained driving.

Cold Air Intake Systems

Cold air intake (CAI) systems relocate the filter outside the engine bay, pulling air from behind the bumper or front fender. This position exposes the intake to cooler, denser air, which supports more complete combustion. On the FA24, well-designed CAI systems have shown gains of 10-15 horsepower at the wheels when paired with proper tuning.

  • Injen SP Series Cold Air Intake – Features a sealed airbox that isolates the filter from engine heat and a mandrel-bent aluminum tube. The Injen SP series includes a hydro-shield for water protection, making it suitable for daily driving in wet conditions. Owners report consistent intake air temperatures 15-20°F lower than under-hood alternatives.
  • AEM Cold Air Intake System – Uses a dry-flow filter that requires no oiling, reducing maintenance. The AEM intake includes a heat shield and uses the factory mounting points for straightforward installation. The filter media flows well while still trapping fine particles.
  • K&N 69 Series Typhoon Intake – Combines a large conical filter with a smooth aluminum tube. While the Typhoon is technically a short ram design, the 69 Series positions the filter in a lower section of the engine bay to access cooler air. K&N's oiled cotton gauze filter provides high flow rates and is serviceable over the life of the vehicle.

Cold air intakes deliver the best results when the vehicle is moving, as airflow through the front bumper forces cool air into the intake location. In stop-and-go traffic, the sealed airbox helps prevent heat soak. For a 300 HP build, a CAI system is strongly recommended over open-element designs due to its consistency under varying conditions.

Short Ram Intake Systems

Short ram intakes keep the filter inside the engine bay, typically mounting directly to the throttle body or mass airflow tube. These systems are easier to install and often cost less than cold air intakes. However, they draw air from the engine bay, which is heat-soaked from the radiator, exhaust, and engine surfaces. On the FA24, short ram intakes generally produce smaller power gains and can actually lose power in hot conditions if the intake air temperatures spike.

  • GReddy SP Elite Short Ram Intake – Built with a carbon fiber tube that resists heat transfer from the engine bay. The GReddy SP Elite includes a large oiled cotton filter and uses a velocity stack at the MAF sensor for accurate airflow readings. Gains are modest, around 5-8 horsepower, but the intake note is more aggressive.
  • Weapon R Secret Weapon Intake – Features a polished aluminum tube and a conical filter with a heat shield. Weapon R offers optional coolant reroute kits that help reduce intake temperatures, but the basic configuration still draws air from the engine bay. This intake is best suited for drivers who prioritize sound and low cost over maximum power.

Short ram intakes can support a 300 HP build, but they require careful attention to under-hood temperatures. Heat-wrapping the intake tube or adding a cold air diversion panel helps. In most dyno comparisons, well-designed cold air intakes outperform short ram units by 5-10 horsepower on the FA24.

Intake Manifold and Throttle Body Upgrades

Once the intake piping and filter are optimized, the intake manifold and throttle body become the next restriction. The factory plastic manifold has reasonable flow, but aftermarket aluminum manifolds with larger plenum volumes and velocity stacks can increase top-end power by 10-15 horsepower. JDL Auto Design and GSX offer billet intake manifolds for the FA24 that are designed for high-flow applications. Combining these with a 70mm or 75mm throttle body from BBK or Skunk2 allows the engine to breathe freely at high RPM. These upgrades are aggressive and should be paired with cam timing adjustments in the tune.

Exhaust Upgrades: Letting It Breathe

The FA24 exhaust system from the factory includes restrictive catalytic converters, a resonator, and a muffler that prioritize noise control over flow. After full intake upgrades, the exhaust side becomes the primary bottleneck. Exhaust system upgrades reduce back pressure and allow the engine to expel combustion gases more efficiently, which directly increases horsepower. The FA24 responds particularly well to improved exhaust flow because of its 2.4-liter displacement and high 12.5:1 compression ratio, which generates significant exhaust energy.

Cat-Back Exhaust Systems

A cat-back exhaust replaces the exhaust pipes from the catalytic converter outlet to the tailpipe. This upgrade typically includes a mid-pipe with a resonator delete or high-flow resonator, a muffler, and tips. Cat-back systems are the most common first exhaust upgrade because they are relatively easy to install, do not affect emissions equipment, and produce noticeable sound improvements. For power, expect gains of 5-10 horsepower with a quality cat-back.

  • Remark Cat-Back Exhaust System – Made from 3-inch mandrel-bent stainless steel tubing, the Remark system includes a mid-pipe with a Helmholtz resonator that cancels drone. The muffler design uses straight-through perforated cores for maximum flow. Owners report a deep, refined tone without excessive cabin noise.
  • Invidia Q300 Cat-Back Exhaust – The Q300 is known for its relatively quiet output compared to other aftermarket systems. It uses 3-inch piping and a large canister muffler with sound-dampening baffles. The fitment is excellent, and the system does not trigger check engine lights.
  • Borla Cat-Back Exhaust System – Borla uses T304 stainless steel and builds its systems with a patented straight-through muffler design. The Borla system produces a pronounced bark at full throttle while remaining quiet at cruise. The multi-chamber design reduces drone effectively.

For a 300 HP goal, a 3-inch cat-back system is recommended. Smaller 2.5-inch systems may restrict top-end power, while 3-inch pipes flow adequately for naturally aspirated builds without sacrificing too much low-end torque.

Axle-Back Exhaust Systems

Axle-back exhausts replace the muffler section only. These are the cheapest exhaust upgrade and do not significantly increase horsepower beyond 2-5 horsepower. Axle-backs change the exhaust tone and save weight, but they do not address restriction in the mid-pipe. For serious power gains, skip the axle-back and go straight to a full cat-back or header-back system.

Headers and Front Pipe

The factory exhaust manifold on the FA24 is a log-style cast iron unit that is heavy, restrictive, and designed for heat management. Aftermarket headers replace this manifold with equal-length or unequal-length tubular runners that significantly reduce back pressure and improve exhaust scavenging. Headers are the single largest bolt-on horsepower gain for the FA24, typically adding 12-18 horsepower after tuning.

  • Nameless Performance Headers – Constructed from 304 stainless steel with mandrel-bent primary tubes. Nameless offers both equal-length and unequal-length designs. The equal-length version maximizes top-end power, while the unequal-length version preserves the classic Subaru rumble. Both designs include thick flanges and slip-fit joints for thermal expansion.
  • PTuning Center Exit Headers – A less common but effective option, PTuning builds headers with a single collector that routes to a center-exit exhaust. This design simplifies the exhaust path and reduces weight.
  • Racer X Fabrication Headers – Offering a budget-friendly option, Racer X headers are made from 321 stainless steel primary tubes and include a high-flow merge collector. These headers are popular with tuners for their balance of flow and cost.

The front pipe connects the header collector to the catalytic converter. Aftermarket front pipes eliminate restrictive bends and use larger diameter tubing. GrimmSpeed and Torque Solutions produce front pipes with high-flow catalytic converters that support power goals without triggering emissions codes. Replacing the factory front pipe and header together can yield a total gain of 15-25 horsepower.

Complete Header-Back vs. Cat-Back Systems

A header-back exhaust combines the headers, front pipe, and cat-back into a single coordinated system. This approach ensures that all components are matched in diameter and bend radius. System manufacturers like HKS and Fujitsubo offer complete header-back packages for the FA24 BRZ that are tuned to work together. For a 300 HP goal, a header-back system eliminates guesswork and prevents bottlenecks from mismatched sections.

Tuning: Unlocking the Full Potential

Hardware upgrades alone do not guarantee 300 horsepower. The factory ECU calibration is tuned for emissions, fuel economy, and conservative ignition timing. After installing a high-flow intake and exhaust, the engine will be moving more air, which changes the fuel mixture requirements and ignition timing windows. Tuning adjusts these parameters to fully exploit the new airflow capacity. Without tuning, a fully built intake and exhaust combination might only gain 20-30 horsepower. With proper tuning, those same parts can produce 50-70 horsepower gains.

ECU Reflashing with ECUTek

ECUTek is the most widely supported tuning platform for the FA24 BRZ. It allows a tuner to modify fuel maps, ignition timing maps, variable valve timing, throttle response, and rev limits. ECUTek also includes features like launch control, flat-foot shifting, and data logging. Most performance shops that specialize in Subaru tuning offer ECUTek calibration. The reflash process involves reading the factory ECU file, modifying it with ECUTek software, and writing the new file back to the ECU. The car remains fully drivable and maintains all factory ECU functions.

ECUTek tuning typically costs between $600 and $1200 for a custom calibration, depending on the tuner's reputation and the number of revisions included. A dyno tune provides the most consistent results because it allows the tuner to hold the engine at specific load points and optimize timing across the entire RPM range. For 300 HP builds, dyno tuning is strongly recommended.

Remote Tuning with OpenFlash

OpenFlash by Vishnu Performance offers a lower-cost alternative for FA24 tuning. The OpenFlash tablet connects to the OBD-II port and allows the user to flash pre-loaded maps or custom tunes. OpenFlash maps are available for common intake and exhaust combinations. Remote tuning allows enthusiasts to send data logs to a tuner, who can then adjust the map and send back a revised file. This approach is viable for bolt-on builds but may not extract the last few horsepower from aggressive setups like ported heads or intake manifold swaps.

Data Logging and Safety

After tuning, data logging is essential to verify that the engine is not experiencing knock, excessive fuel trims, or high exhaust gas temperatures. ECUTek and OpenFlash both include logging capabilities. Key parameters to monitor include knock correction values, lambda readings, intake air temperature, coolant temperature, and fuel pressure. If any parameter exceeds safe thresholds during hard driving, the tune should be revised before continuing to push for higher power levels.

Supporting Modifications for a Reliable 300 HP Build

Reaching 300 horsepower requires addressing supporting systems that become stressed under increased power. The factory fuel system, clutch, and cooling system may all need upgrades to maintain reliability at this output level.

  • Fuel System – The stock fuel pump and injectors can supply enough fuel for approximately 280-290 wheel horsepower on the FA24. Beyond that point, fuel pressure can drop, causing lean conditions under load. A DW300c or AEM 340LPH fuel pump and ID1050x or FIC 1000cc injectors provide headroom for 300-350 horsepower. Flex fuel capability (E85) is also available with these injectors and a tune.
  • Oil Cooling – Sustained high-RPM operation generates more heat. The factory oil cooler may be inadequate for track use. An aftermarket oil cooler kit from Mishimoto or Setrab with a thermostatic sandwich plate helps maintain consistent oil temperatures.
  • Clutch – The factory clutch can handle around 280-300 lb-ft of torque. At 300 horsepower, peak torque may exceed the clutch's holding capacity, especially with aggressive launches. A performance clutch kit from ACT or Exedy is a worthwhile upgrade.
  • Weight Reduction and Tires – Power-to-weight ratio matters. Removing unnecessary weight from the interior, using lightweight wheels, and fitting high-performance tires such as Michelin Pilot Sport 4S or Bridgestone Potenza RE-71RS improve acceleration and lap times without adding horsepower.

Building a 300 HP Roadmap

The most reliable path to 300 wheel horsepower on the FA24 BRZ follows a staged approach that builds on itself. Starting with the intake and exhaust foundation, then moving to tuning and supporting mods, produces consistent results.

  • Stage 1: Intake + Exhaust – Cold air intake and cat-back exhaust. Expected gain: 10-15 hp. Total: 240-245 whp.
  • Stage 2: Headers + Front Pipe + Tune – Add aftermarket headers and front pipe with ECUTek dyno tune. Expected gain: 25-35 hp. Total: 270-280 whp.
  • Stage 3: Intake Manifold + Throttle Body + Fuel System – Upgrade intake manifold, throttle body, fuel pump, and injectors. Re-tune for peak output. Expected gain: 15-20 hp. Total: 295-300+ whp.

This staged approach allows you to verify each component's contribution and avoids over-spending on parts that do not align with your driving goals. Many owners find that Stage 2 provides a satisfying power increase for street use, while Stage 3 delivers the full 300 HP experience.

Conclusion

Achieving 300 horsepower on a Subaru BRZ FA24 requires a coordinated selection of intake and exhaust upgrades matched with professional tuning. Cold air intake systems, header-back exhaust configurations, and ECUTek calibration form the proven foundation for this power level. Supporting modifications in fuel delivery, cooling, and clutch capacity ensure that the build remains reliable under hard use. By following a staged plan and investing in quality components, you can unlock the full potential of the FA24 and enjoy a noticeably faster, more responsive BRZ.

For further reading on specific tuning strategies and community build threads, check out FT86Club's FA24 performance section, Subaru Parts' FA24 upgrade guide, and ECUTek's official training resources.