The Subaru BRZ and the FA24 Engine

The second-generation Subaru BRZ, introduced for the 2022 model year, marked a significant departure from its predecessor by adopting a larger 2.4-liter flat-four engine, designated the FA24. This powerplant replaced the earlier 2.0-liter FA20, addressing one of the primary criticisms of the first-generation car: a perceived lack of low-end torque. The FA24 produces 228 horsepower and 184 lb-ft of torque from the factory, a substantial improvement over the previous engine's 205 horsepower and 156 lb-ft. While these numbers are respectable, the FA24 responds exceptionally well to modifications that improve airflow. One of the most accessible and effective upgrades for owners seeking additional performance is a high-flow cold air intake system from Injen Technology. With documented gains approaching 50 horsepower at the wheels when paired with proper calibration, the Injen intake has become a staple modification for BRZ enthusiasts who want to extract more from their naturally aspirated flat-four.

Understanding the FA24 Engine Architecture

The FA24 engine belongs to Subaru's FA series of direct-injection flat-four engines. It features a 94mm bore and 86mm stroke, giving it a displacement of 2387cc. The engine uses a dual overhead camshaft design with Subaru's AVCS (Active Valve Control System) on both intake and exhaust camshafts, allowing variable valve timing across all four cam profiles. The compression ratio sits at 12.5:1, which is relatively high for a naturally aspirated production engine, contributing to its thermal efficiency.

What makes the FA24 particularly receptive to intake modifications is its factory tuning philosophy. Subaru engineers optimized the stock calibration for a broad torque curve and emissions compliance, which means the intake and exhaust systems include several restrictions. The factory airbox, while functional, creates a pressure drop that limits volumetric efficiency at higher RPM ranges. By reducing this restriction with a properly designed aftermarket intake, you allow the engine to ingest a greater mass of air per cycle, which directly translates to increased power output.

Airflow Dynamics and the Intake System

The relationship between airflow and power in an internal combustion engine follows fundamental principles of thermodynamics. An engine is essentially an air pump; the more air you can move through it, the more fuel you can burn, and the more power you can produce — provided the air-fuel ratio remains within a safe and efficient range. The stock intake system on the BRZ uses a complex resonator and baffle arrangement designed to reduce noise and smooth out airflow pulsations. While these features improve the daily driving experience, they create turbulence and restriction that rob the engine of potential power.

The Injen intake system addresses these issues by providing a larger diameter, smoother intake path, and a high-flow air filter that reduces pressure drop. The system is designed to draw air from a cooler region of the engine bay, which increases air density. Denser air contains more oxygen molecules per unit volume, allowing for more complete combustion and greater power output. This combination of reduced restriction and cooler intake air temperatures forms the basis for the power gains observed with the Injen system.

Injen Technology: Engineering and Design Philosophy

Injen Technology has been a prominent name in the performance intake market for over two decades. The company is known for its focus on research and development, utilizing computational fluid dynamics (CFD) and extensive dyno testing to refine its products. The BRZ FA24 intake system reflects this engineering-driven approach. The intake tube is constructed from high-density cross-linked polyethylene, which offers excellent thermal resistance and structural integrity. The material does not conduct heat as readily as aluminum, helping to keep intake air temperatures lower during sustained driving.

The filter element uses a multi-layer cotton gauze design that provides high airflow capacity while maintaining effective filtration. Injen claims a 99.6% filtration efficiency rating for its filters, which is critical for engine longevity. The filter is oiled, and the company provides a cleaning and re-oiling kit for maintenance. The system also includes a heat shield that isolates the filter from radiant engine heat, further reducing intake air temperatures. This heat shield is precision-molded to fit the BRZ's engine bay and uses gasketing to form a seal against the hood line.

The Injen Intake vs. Other Options

Several manufacturers offer intake systems for the FA24 BRZ, but the Injen system distinguishes itself through its combination of low restriction and effective heat management. Some competitors use metal intake tubes that can heat soak in traffic or during extended track sessions, actually increasing intake air temperatures relative to the stock system. Injen's cross-linked polyethylene material mitigates this issue. Additionally, the Injen system is designed to work with the factory engine calibration, meaning it provides gains without requiring an immediate tune. However, like any free-flowing intake, maximum gains are realized with custom calibration that adjusts fuel and ignition timing to take full advantage of the increased airflow.

Quantified Performance Gains: Dyno Results and Analysis

Independent dyno testing of the Injen intake on the FA24 BRZ has yielded consistent results. On a typical chassis dynamometer, a stock BRZ produces somewhere in the range of 200-210 horsepower at the wheels, accounting for drivetrain losses that typically amount to about 12-15% of the engine's rated 228 horsepower. After installation of the Injen intake alone — without any other modifications or tuning — owners have reported gains of 12-18 wheel horsepower across the mid-range and top-end.

Peak Gains with Tuning

The most impressive results come when the Injen intake is paired with a custom ECU tune. With calibration optimized for the increased airflow, the FA24 can produce up to 50 horsepower over stock at the wheels. This figure represents the combined benefit of the intake and tuning, with the intake contributing roughly 15-20 horsepower on its own and the tune adding another 30-35 horsepower through optimized ignition timing, fuel delivery, and camshaft phasing. The torque curve also shifts upward, with peak torque rising by approximately 25-30 lb-ft and arriving lower in the RPM range.

  • Stock (engine rated): 228 hp / 184 lb-ft
  • Injen Intake only (at wheels): 215-220 hp / 170-175 lb-ft
  • Injen Intake with tune (at wheels): 245-255 hp / 195-205 lb-ft
  • Peak gain over stock (with tune): 45-50 hp at the wheels

These numbers represent the typical range seen on mustang-style dynos, which tend to read lower than Dynojet dynos. On a Dynojet, peak wheel horsepower numbers can be 5-10% higher. Regardless of the measurement standard, the trend is clear: the Injen intake unlocks significant additional performance from the FA24 engine, especially when combined with proper calibration.

Installation: What to Expect

Installing the Injen intake on a BRZ FA24 is a straightforward process that most enthusiasts can complete in one to two hours with basic hand tools. The system uses a direct-fit design that does not require cutting or modification of the factory components. The process involves removing the stock airbox assembly, including the intake tube that connects to the throttle body. All factory mounting points are retained, and the Injen system bolts directly into place.

Step-by-Step Installation Overview

The installation begins with disconnecting the negative battery terminal to reset the ECU and prevent any electrical issues during the work. The factory intake system is removed by disconnecting the mass airflow sensor (MAF) electrical connector, unclipping the airbox retaining clips, and unbolting the intake tube from the throttle body. The factory rubber coupler at the throttle body is reused with the Injen system, ensuring a leak-free seal.

Once the stock components are removed, the Injen heat shield is installed onto the factory mounting studs. The intake tube is then positioned and secured with the provided silicone couplers and stainless steel T-bolt clamps. The MAF sensor is transferred from the factory airbox to the Injen tube, and the filter is attached to the end of the tube using the provided coupler. Finally, all connections are verified, the battery is reconnected, and the vehicle is started to check for any leaks or abnormal sounds.

Most owners report that the installation is intuitive and well-documented with the instructions included in the kit. No specialized tools beyond a socket set, screwdrivers, and pliers are required. The entire process is reversible, allowing owners to return to the factory intake if desired.

Sound Quality and Driving Experience

One of the most immediately noticeable changes after installing the Injen intake is the sound. The FA24 engine has a distinctive flat-four exhaust note, but its intake noise is relatively subdued from the factory. The Injen intake amplifies the induction noise, producing a pronounced sucking sound under hard acceleration that transitions into a deeper, more aggressive note at higher RPM. This audible feedback enhances the driving experience by providing a sensory connection to the engine's operation.

Many owners describe the sound as reminiscent of a vintage sports car or a racing engine, with a pronounced induction roar that is distinct from the exhaust note. The sound is most prominent between 4000 and 7000 RPM, during which the throttle response also feels sharper. Part-throttle driving below 3000 RPM produces a modest increase in intake noise that is not intrusive for daily driving. This characteristic makes the Injen intake suitable for both street and occasional track use.

Impact on Throttle Response and Drivability

Beyond the peak power gains, the Injen intake improves the BRZ's throttle response, particularly in the mid-range. The reduction in intake restriction allows the engine to respond more quickly to changes in throttle position. This improvement is noticeable when exiting corners or performing quick overtaking maneuvers. The FA24's factory calibration includes some throttle lag to smooth out drivability, and the intake's increased airflow reduces this lag slightly.

The torque curve also benefits from the reduced restriction. While peak torque gains are modest without tuning, the torque curve fills out across the entire operating range. This means the engine feels stronger from idle to redline, with a particular improvement in the 3000-5000 RPM range where daily driving occurs. The engine does not feel flat or peaky; instead, it pulls smoothly and consistently to the redline.

Fuel Efficiency Considerations

A common question among owners considering an intake upgrade is the effect on fuel economy. The Injen intake, by reducing pumping losses, can improve volumetric efficiency, which generally allows the engine to produce the same power with less throttle opening. In theory, this can improve fuel economy during steady-state cruising. In practice, many owners find that the improved sound and performance encourage more aggressive driving, which tends to reduce fuel economy.

However, with disciplined driving, some owners report slight improvements in highway fuel economy — typically 1-3 miles per gallon — due to the reduced pumping losses. City driving fuel economy tends to remain unchanged or decrease slightly due to the higher power output used during acceleration events. On balance, the fuel economy impact is neutral for most drivers, as the intake does not change the engine's base fuel map without tuning.

Maintenance and Long-Term Care

The Injen intake requires periodic maintenance to maintain its performance. The cotton gauze air filter should be cleaned and re-oiled every 30,000 to 50,000 miles, depending on driving conditions. Injen sells a cleaning kit that includes a specialized cleaner and filter oil. The process involves spraying the cleaner onto the filter, allowing it to soak for 10 minutes, rinsing with low-pressure water, and allowing the filter to dry naturally. Once dry, the filter oil is applied evenly across the gauze material. The kit provides sufficient oil for multiple cleanings.

The intake tube and heat shield should be inspected during filter maintenance for any signs of wear or loose connections. The silicone couplers may soften over time, but they typically last the life of the vehicle. It is advisable to check the T-bolt clamps every few thousand miles to ensure they remain tight, as thermal cycling can cause slight loosening. Overall, the Injen intake is a low-maintenance modification that provides reliable performance over the long term.

Real-World Owner Experiences

Subaru BRZ owners who have installed the Injen intake consistently report high levels of satisfaction. A common theme in owner reviews is the transformation of the car's character. The intake does not just add power; it changes how the engine feels and sounds, making the driving experience more engaging. Many owners note that the car feels noticeably quicker in daily driving scenarios, particularly when merging onto highways or climbing steep grades.

Owners who track their BRZs report that the intake performs well under sustained high-load conditions, maintaining consistent intake air temperatures without significant heat soak. The heat shield is effective at blocking radiant heat from the engine, and the cross-linked polyethylene intake tube does not heat soak like aluminum tubes. This thermal stability is important for track enthusiasts who push the car for extended sessions.

Some owners combine the Injen intake with exhaust modifications and tuning for a comprehensive naturally aspirated build. In these configurations, the intake provides a foundation for additional power gains, as the engine's breathing system becomes a cohesive whole rather than a bottleneck. The intake's compatibility with other modifications is a strength, as it does not require any specific supporting mods to function properly.

Cost-Value Analysis

The Injen intake for the BRZ FA24 is priced competitively within the intake market. When compared to other cold air intake systems that offer similar features, the Injen system typically represents a good value. The inclusion of a high-quality filter, precision-molded heat shield, and durable intake tube justifies the cost. The long-term value is enhanced by the ability to clean and re-oil the filter rather than replacing it, reducing ongoing costs.

When considering the cost per horsepower gained, the Injen intake is one of the most cost-effective modifications available for the FA24 BRZ. The 12-18 wheel horsepower gain without tuning translates to roughly $30-50 per horsepower, which is excellent value compared to other performance modifications such as exhaust systems or header upgrades. With tuning, the cost per horsepower drops even lower, making the intake an attractive first step for any performance build.

Compatibility with Other Modifications

The Injen intake is designed to work with the factory engine bay layout and does not interfere with other common modifications. It is compatible with aftermarket strut tower bars, oil catch cans, and most aftermarket engine covers. The system does not require relocation of any factory components, and it does not interfere with the operation of the hood latch or hood clearance. This compatibility simplifies the build process for owners planning multiple modifications.

For owners considering forced induction in the future, the Injen intake can be repurposed as a supporting mod. While most turbo or supercharger kits include their own intake piping, the Injen filter and heat shield can often be used with these systems. This flexibility adds to the long-term value of the investment.

The FA24 Platform and Future Potential

The Subaru BRZ with the FA24 engine has quickly established itself as a strong platform for naturally aspirated performance tuning. The engine's robust bottom end, high compression ratio, and responsive valvetrain make it ideal for intake and exhaust modifications. The Injen intake represents a foundational upgrade that unlocks the engine's potential without requiring major disassembly or expensive supporting modifications.

As the aftermarket continues to develop parts for the FA24, the Intake will remain a staple recommendation for owners seeking a meaningful performance improvement. The combination of power gains, improved sound, and straightforward installation makes it a compelling choice for both novice and experienced enthusiasts. For anyone looking to get more out of their BRZ, the Injen intake is a logical and rewarding starting point.