The Subaru BRZ, especially with its latest FA24 engine, has become a favorite among driving purists and performance enthusiasts. While the factory 2.4-liter boxer engine delivers a commendable 228 horsepower, the platform responds exceptionally well to bolt-on modifications. Upgrading the intake, exhaust, and tuning can unlock a noticeably sharper throttle response, more mid-range punch, and a more engaging exhaust note. This guide provides a thorough, step-by-step walkthrough for beginners who want to perform a basic bolt-on performance installation on a BRZ FA24. By following these instructions carefully, you can complete the job safely and avoid common pitfalls that plague first-time installers.

Understanding the BRZ FA24 Engine

The FA24 is a 2.4-liter, naturally aspirated, horizontally opposed (boxer) four-cylinder engine. It replaced the older 2.0-liter FA20 in the second-generation BRZ, bringing a significant displacement bump and torque increase. Key characteristics that affect performance modifications include:

  • Direct Injection (DI) Only: Unlike some Subaru engines that combine port and direct injection, the FA24 relies solely on direct injection. This demands careful fuel system management when tuning and makes it sensitive to fuel quality.
  • High Compression Ratio: With a compression ratio of 12.5:1, the FA24 already runs tight tolerances. Adding too much ignition timing without proper tuning can lead to knock or pre-detonation.
  • Plastic Intake Manifold: The stock intake manifold is designed for low-end torque and NVH reduction. Aftermarket intakes often replace the entire tract for improved airflow, but may require careful heat management.
  • Exhaust System Layout: The FA24 features a single exhaust port per cylinder head and a fairly restrictive factory exhaust system. The catalytic converter and secondary cat create significant backpressure, which removal or replacement of can free up power.

Understanding these aspects helps you choose compatible parts and anticipate challenges during installation. For deeper technical details on the FA24 engine architecture, consult resources like the Subaru engineering site or dedicated forums such as FT86Club.

Tools and Materials Needed

Before you begin, assemble all required tools and materials. Having everything on hand prevents frustrating mid-project trips to the hardware store. Below is a comprehensive list with recommendations.

Essential Hand Tools

  • Socket Set (Metric and SAE): You'll need 8mm, 10mm, 12mm, 14mm, 17mm, and 19mm sockets. A 3/8” drive set covers most fasteners. A 1/2” drive breaker bar helps with stubborn bolts.
  • Torque Wrench: Critical for tightening bolts to manufacturer specifications, especially exhaust manifold nuts and intake mounting bolts. A 3/8” drive torque wrench covering 10–80 ft-lb is ideal.
  • Wrenches: Combination wrenches in 10mm, 12mm, 14mm, and 17mm. For exhaust work, a crowfoot wrench or ratcheting wrench helps in tight spaces.
  • Screwdrivers: Phillips and flathead in various sizes for removing clips and minor trim.
  • Pliers: Needle-nose pliers for hose clamps, and slip-joint pliers for loose fasteners.
  • Trim Removal Tools: A plastic pry tool set prevents damage to interior panels when removing the intake resonator or battery box.

Specialty Items

  • O2 Sensor Socket: Required for removing the downstream oxygen sensors from the exhaust system. A 22mm offset socket works best.
  • Jack and Jack Stands: If you are replacing the entire exhaust system (cat-back or header-back), raising the vehicle safely is mandatory. Use six-ton stands on a level surface.
  • OBD-II Scanner: A basic scanner allows you to clear diagnostic trouble codes (DTCs) after disconnecting the battery and verify that no new codes appear after the installation.

Performance Parts (Example Kit)

  • Cold Air Intake: A system that relocates the air filter into the fender or behind the bumper for cooler, denser air.
  • Cat-Back Exhaust: Replaces the entire exhaust from the catalytic converter back. Produces a sportier note and reduces backpressure.
  • Performance Header: An equal-length or unequal-length header that frees up exhaust flow. Note: Removing the factory primary catalytic converter will require a tune and may violate emissions laws in some regions.
  • ECU Tuning Device: A handheld programmer like the COBB Accessport V3 allows you to flash pre-loaded or custom tunes that optimize air/fuel ratios for the new parts.

For a detailed tool checklist specific to the FA24, refer to the COBB Tuning BRZ installation guides.

Step 1: Preparing Your Workspace

A clean, organized workspace reduces the risk of losing small parts and prevents contamination of the engine bay. Follow these guidelines.

Safety First

  • Always wear safety glasses and heavy-duty work gloves. The FA24 engine bay contains sharp edges and hot surfaces even when the engine is cold.
  • Work in a well-ventilated area. Exhaust fumes and fuel vapors can accumulate. If using a garage, keep the door open or use a ventilation fan.
  • Ensure the parking brake is firmly engaged and chock the rear wheels. If lifting the vehicle, use jack stands at the specified lift points under the frame rails.

Layout and Lighting

Clear the area of clutter. Lay down a drop cloth or cardboard to catch any spilled coolant or oil. Position a bright work light or headlamp for cast shadows under the hood. Organize your tools on a magnetic tray or in a rolling cart so you can reach them without leaving the vehicle.

Battery Disconnect

Before touching any electrical connectors or sensors, disconnect the negative battery terminal. This prevents accidental short circuits and resets the ECU's learned fuel trims, which is beneficial when installing new parts. Wait at least 10 minutes after disconnecting to allow the capacitor in the ECU to discharge.

Step 2: Removing the Stock Parts

With the workspace prepared, begin removing the factory intake and exhaust components. Work methodically and label all connectors and brackets.

Removing the Stock Intake System

  1. Remove the engine cover: The plastic cover on top of the engine pulls straight up. It is held by four press-in grommets.
  2. Disconnect the intake tube: Loosen the clamp at the throttle body and at the airbox. Use a flathead screwdriver to pry the rubber hose off gently.
  3. Unplug the MAF sensor: Carefully depress the tab on the mass airflow sensor connector and unplug it. Do not pull the wires. Note: The MAF sensor is delicate; avoid touching the sensing element.
  4. Remove the airbox assembly: The lower half of the airbox is secured by two 10mm bolts and a rubber grommet on the fender. Lift it out carefully.
  5. Remove the intake resonator: Underneath the airbox is a plastic resonator chamber. It may require removing a 12mm bolt near the driver-side wheel well. Pry it loose from its mounting hole.

Removing the Stock Exhaust System (Cat-Back)

If you are replacing only the cat-back portion, you do not need to remove the header or the front pipe. For a full exhaust swap, follow the cat-back removal steps first, then proceed to the header.

  1. Jack up the rear of the vehicle: Place jack stands under the rear frame rails. Ensure the car is stable.
  2. Spray exhaust bolts with penetrating oil: Use a product like WD-40 Specialist or PB Blaster on the flange bolts and hanger studs. Let it soak for 10 minutes.
  3. Remove the exhaust hangers: The rubber isolators that hold the exhaust to the chassis can be pried off with a flathead screwdriver or using a hanger removal tool. Start from the rear muffler section.
  4. Unbolt the rear muffler section: The muffler is bolted to the mid-pipe with two 14mm bolts. Support the muffler with a jack or second person before removing the last bolt.
  5. Unbolt the mid-pipe: The mid-pipe connects to the front pipe (or header) via a 14mm or 17mm flange. The O2 sensor wire must be unclipped from its bracket on the mid-pipe. Slide the sections apart.
  6. Remove the front pipe (if applicable): The front pipe connects the header to the mid-pipe and contains the first catalytic converter. This section requires accessing bolts from both the engine bay and underneath. Be prepared for stubborn bolts—use a breaker bar.

Note: If you plan to reinstall the stock parts later, keep all bolts and gaskets in a labeled bag. Discard old gaskets—they should not be reused.

Step 3: Installing Performance Parts

Installation is essentially the reverse of removal, but with important differences. Follow the manufacturer’s instructions for each part, especially regarding gasket orientation and torque specifications.

Installing the Cold Air Intake

  1. Mount the intake box: Many aftermarket intakes use a heat shield that bolts to the existing airbox mounting points. Ensure the shield does not contact the hood when closed.
  2. Install the intake tube: Slide the silicone coupler over the throttle body first. Tighten the clamp snugly but do not fully torque yet. Attach the other end to the MAF housing on the airbox.
  3. Position the MAF sensor: Carefully insert the MAF sensor into the MAF housing (usually located on the intake tube). The sensor must be oriented exactly as marked—usually with an arrow pointing upstream. Tighten the retaining screws to 2.5 ft-lb; overtightening can damage the sensor.
  4. Connect vacuum lines: Some intakes include a port for the crankcase ventilation hose. Attach the factory hose with the supplied clamp. Double-check that all hoses are routed away from the serpentine belt.
  5. Final torque: Tighten all clamps to the spec in the instructions (typically 4–6 ft-lb). Reinstall the engine cover if it clears the new intake.

Installing the Performance Exhaust

  1. Install gaskets: Use new metal-wire ring gaskets at each flange joint. Do not use RTV gasket sealer unless specified.
  2. Start from the front: If you are replacing the header, loosely bolt the header to the cylinder head with the supplied gasket. Use a crisscross pattern and leave bolts hand tight.
  3. Attach the front pipe (if replacing): Bolt the front pipe to the header flange. Again, hand tighten only.
  4. Attach the mid-pipe and muffler: Slide the mid-pipe into the front pipe hanger. Hang the muffler on the four rubber isolators (this often requires lubricating the hangers with silicone spray).
  5. Tighten in sequence: Starting from the header, tighten all bolts to the specified torque (typically 25–35 ft-lb for flange nuts). Then tighten the hanger brackets. Reinstall the O2 sensor by hand to avoid cross-threading, then torque to 30 ft-lb.
  6. Check clearance: Rotate the steering wheel full lock in both directions and inspect the mid-pipe for contact with the steering shaft or brake lines. Reposition if necessary.

For torque values, always verify with the manufacturer’s data sheet. An excellent resource for OEM torque specs is the Subaru Online Parts torque document.

Step 4: Reconnecting and Testing

Once all the hard parts are installed, carefully reconnect everything before starting the engine.

  1. Reconnect the battery: Tighten the negative terminal to 6–8 ft-lb. Do not over-torque, as the terminal can crack.
  2. Check all electrical connectors: Ensure the MAF sensor, O2 sensors, and any other harness clips are fully seated. Listen for a click.
  3. Inspect all hoses and clamps: Look for loose silicone couplers, pinched vacuum lines, or exhaust leaks. A smoke test is ideal but not required; you can use a spray bottle of soapy water on the intake joints.
  4. Prime the oil system: Crank the engine for 10–15 seconds without starting (disable the fuel pump or pull the fuel pump relay). This circulates oil to the new components before first start.
  5. Start the engine: Allow it to idle for 30 seconds. Listen for unusual rattles (loose heat shield) or whistles (intake leak). A slight exhaust smell is normal as the new gaskets seat.
  6. Check for leaks: While the engine runs, look under the car for any dripping coolant, oil, or exhaust smoke at flanges. Use a rag to wipe suspect joints—if it’s wet, retorque the bolts.
  7. Reflashing the ECU: If you installed a header or intake that removes a catalytic converter, you must flash a tune. Use your OBD-II device to load the appropriate base map. Follow the device’s instructions carefully. Never drive the car without a tune if you have changed the air/fuel ratio significantly.

Step 5: Fine-Tuning and Adjustments

After the initial startup and test drive, fine-tuning maximizes performance gains and reliability.

Data Logging

Use your OBD-II scanner or tuning platform to log key parameters on a short drive: intake air temperature (IAT), coolant temperature, fuel trims (STFT and LTFT), ignition timing, and knock correction (feedback knock and fine knock learn). If you see persistent negative knock correction values above -1.0 degrees, you likely need a custom tune from a professional. Resources like Tuning Technologies offer remote custom tunes for the FA24.

Adjusting Intake Positioning

If intake air temperatures climb above ambient by more than 15°F while driving, the heat shield may be leaking hot air. Add closed-cell foam weatherstripping around the edges of the heat shield to seal against the hood or engine block.

Twisting Exhaust Hangers

If the exhaust rattles against the underbody, you can adjust the hanger positions by twisting the rubber isolators. Alternatively, replace with urethane hangers for a firmer, rattle-free setup.

Checking for Error Codes

After a few drive cycles, check for pending codes. Common issues include:

  • P0171/P0172 (Lean/Rich codes): Caused by a vacuum leak or improperly configured MAF scaling. Inspect all silicone couplers.
  • P0420 (Catalyst efficiency below threshold): This appears after removing a catalytic converter. A proper tune should disable this code via rear O2 sensor defeat or high-flow cat specifications.
  • P050A (Cold start idle air control): May occur if the intake adaptation is still learning. Drive for 50 miles to allow the ECU to relearn.

Conclusion

Installing performance parts on your BRZ FA24 is one of the most rewarding DIY projects you can take on. With careful preparation, the right tools, and patience, even a beginner can achieve professional results. Remember that the engine’s high compression and direct injection system demand respect—always use a quality tune when replacing the intake or exhaust. The modifications described in this guide will transform your BRZ into a more responsive, more exciting vehicle while still retaining daily usability.

If you encounter challenges during installation, do not hesitate to consult online forums like FT86Club or local performance shops. A professional tuner’s input on the final calibration can make the difference between a good build and a great one. Enjoy the process, take your time, and drive safely.