Introduction

The Subaru BRZ with the FA24 engine is a driver’s car right out of the box, but serious enthusiasts know that the induction system leaves power on the table. The Injen Cold Air Intake is one of the most effective bolt‑on upgrades for the FA24, delivering sharper throttle response, a more aggressive intake note, and measurable horsepower gains. This guide walks you through every detail of the installation, from preparation to final tuning considerations. Whether you’re a seasoned DIYer or a first‑time modifier, you’ll learn how to install the Injen intake correctly and safely, ensuring maximum performance and reliability.

Why Upgrade to a Cold Air Intake?

The stock intake system on the FA24 is designed for low noise, low cost, and emissions compliance, not peak output. It uses a restrictive air box and convoluted ducting that heats incoming air and limits flow. A cold air intake like Injen’s replaces the entire path from the front grille to the throttle body with a larger, smoother tube and a high‑flow filter. The key benefits include:

  • Increased Airflow – The larger diameter tube and low‑restriction filter allow the engine to breathe more freely, especially above 4,000 rpm.
  • Colder Air Density – By drawing air from outside the engine bay (or through an enclosed heat shield), the intake reduces charge temperatures, which reduces knock tendency and allows the ECU to advance timing.
  • Improved Throttle Response – Less restriction and a smoother path mean the engine reacts faster to pedal inputs.
  • Aggressive Induction Sound – The open intake makes the boxer engine’s natural growl much more audible, especially under heavy throttle.

Injen’s SP series for the BRZ FA24 is one of the most popular kits because it is CARB‑exempt (pending), dyno‑proven for gains of 10–15 hp at the wheels, and includes a reusable dry‑type filter that never needs oiling.

Tools and Materials Needed

Before you start, gather everything listed below. Having the right tools on hand avoids frustrating mid‑job trips to the hardware store.

  • Injen Cold Air Intake Kit (part number SP1093P for FA24 BRZ)
  • Socket set with 8mm, 10mm, 12mm, and 14mm sockets
  • Ratchet wrench and extensions
  • Flathead screwdriver (medium size)
  • Phillips head screwdriver (No. 2)
  • Torque wrench (ft‑lb and in‑lb ranges)
  • Metric hex key set (for heat shield brackets)
  • Panel clip removal tool (optional, for plastic retainers)
  • Heat‑resistant gloves
  • Safety glasses
  • Shop rags

Also note the torque specifications for critical fasteners: intake tube clamps should be tightened to 35–45 in‑lb; heat shield bolts to 40–50 in‑lb; battery terminal to 60–80 in‑lb. Never overtighten the tube clamps, as they can distort the silicone couplers.

Preparation

Park the BRZ on a level surface and allow the engine to cool completely (at least an hour after driving). A hot engine can burn you and also makes rubber hoses more pliable and likely to tear. Disconnect the negative battery terminal first thing, even before removing anything else, to prevent any short circuits when working near sensors or the MAF. Wrap the disconnected terminal with a rag or place it in a location where it cannot accidentally touch the battery post.

Clear the area around the left side of the engine bay (where the intake sits). You may want to remove the plastic cowl cover above the radiator for easier access to the stock intake snorkel – not strictly required, but it saves time later. Lay out the Injen kit components and verify them against the included instruction sheet.

Step 1: Remove the Engine Cover

Start by removing the decorative engine cover. It is held by four 10mm bolts. Use a socket and ratchet to remove them, then lift the cover straight up. Set it aside in a safe place. While you are here, inspect the rubber grommets that the cover bolts go into; if any are missing or cracked, order replacements before reassembly.

Step 2: Remove the Stock Intake System

The FA24 stock intake consists of three main pieces: the air box (with filter), the intake tube that goes from the box to the throttle body, and the snorkel that draws air from the grille. Proceed in this order:

2a. Remove the Snorkel

Use a flathead screwdriver to loosen the clamp connecting the snorkel to the air box lid. Pull the snorkel forward (toward the grille) and wiggle it free. It has two rubber grommets that pop into the radiator support – just pull firmly but steadily. Set the snorkel aside.

2b. Unbolt the Air Box

The air box lid is held by a few Phillips screws (typically two at the front, one at the rear) and a rubber hose that connects from the valve cover to the intake tube. Disconnect the small breather hose by squeezing the release tab if present, or simply pull it off. Remove the screws and lift the lid. Inside you’ll find the stock air filter – remove it and discard or keep as a spare. The bottom half of the air box (the housing) is held by two 10mm bolts at the bottom and a push‑pin clip. Remove these and pull the housing out of the engine bay.

2c. Remove the Intake Tube

Loosen the big clamp at the throttle body end of the intake tube. The tube is also connected to the crankcase ventilation hose (PCV) – detach this hose by pulling it off. Then slide the intake tube off the throttle body. You may need to rotate it to clear the radiator hose. With all connections free, remove the tube from the engine bay.

Tip: Take a photo of the stock setup before you start. This helps you route the new intake correctly and reminds you where every breather hose goes.

Step 3: Install the MAF Sensor into the Injen Tube

Before fitting the new intake, you need to transfer the Mass Air Flow (MAF) sensor from the stock tube to the Injen tube. The Injen tube has a dedicated MAF boss with two screws. Carefully remove the MAF sensor from the stock tube using a Phillips screwdriver – do not force it, and do not touch the sensor element. Install it into the Injen tube using the supplied screws. Ensure the sensor’s orientation matches the arrow on the tube (should be pointing toward the throttle body). Injen provides a new gasket – reuse it if included, or your old one if properly seated. Torque the screws to 7–10 in‑lb – just snug enough that the sensor doesn’t wobble.

Step 4: Mount the Injen Heat Shield

The Injen kit comes with a powder‑coated aluminum heat shield that separates the filter from the hot engine bay air. Position the heat shield into the area where the stock air box used to sit. It typically attaches using the factory air box mounting holes and one additional bracket that connects to the inner fender. Use the supplied hardware and torque to 40–50 in‑lb. Do not fully tighten until you have the intake tube in place and can confirm the heat shield is aligned with the tube’s air filter location.

Step 5: Install the Injen Intake Tube

Slide the silicone coupler (with the included clamps loosely tightened) over the throttle body end of the Injen tube. Fit the other end of the tube into the filter location inside the heat shield – you may need to temporarily hold the tube while you connect it. At the throttle body, push the tube with coupler onto the throttle body neck, then slide the coupler over the throttle body and tighten the two hose clamps alternately to 35–45 in‑lb. Ensure the tube does not contact the radiator hose or the A/C line – if it does, loosen and rotate the tube slightly.

Now attach the large silicone coupler and included reducer (if any) to the MAF end of the tube. The Injen kit may use a single coupler with a step to match the tube and throttle body diameter – follow the included diagram carefully. Once the tube is firmly connected at both ends, go back and tighten the heat shield bolts fully.

Step 6: Attach the Air Filter and Breather Hoses

Slide the Injen dry‑type air filter onto the open end of the intake tube inside the heat shield. Secure it with the provided hose clamp, tightening just enough to hold it without crushing the filter neck. Do not overtighten.

Connect the crankcase ventilation hose (PCV) from the engine to the nipple on the Injen tube – if the factory hose is too short, the kit includes a piece of hose and a connector to extend it. Similarly, if there are secondary vacuum ports (some FA24 engines have a small hose to the intake manifold), connect those. Close all connections tightly – any vacuum leak will cause rough idle and lean codes.

Step 7: Reconnect Battery and Double‑Check Everything

Make sure all clamps are tightened, hoses are connected, and no tools are left in the engine bay. Reconnect the negative battery terminal and torque it to 60–80 in‑lb. Replace the engine cover if you wish – it still fits over the new intake, though some owners leave it off for easier access and better sound transmission. If you do put it back, align the four bolts and tighten them by hand until snug (do not overtorque).

Step 8: Start the Engine and Check for Leaks

Start the engine. It may take a few extra cranks as the ECU adapts to the new airflow. Once it runs, let it idle for a minute. Listen for any hissing sounds that indicate a vacuum leak. Check all couplers and hose connections by feel – you should not feel any air escaping. If the idle is rough, shut off the engine and double‑check the MAF sensor installation and all clamps.

Allow the engine to reach operating temperature. While it idles, examine the area around the throttle body, the MAF sensor, and the filter for any signs of loose fittings. After the first few minutes, rev the engine gently to 2,000–3,000 rpm a few times, listening for any abnormal whistling or fluttering – that could be a loose clamp or a misaligned tube.

Step 9: First Drive and Adaptation

Take the BRZ for a 10‑mile test drive that includes both city and highway conditions. The ECU will need a few drive cycles to fully adapt to the increased airflow. You may notice slightly different throttle response from the first mile – this is normal. On the FA24, the ECU is quite adaptive; within 50 miles it will typically adjust fueling and timing to take advantage of the intake.

If you feel any hesitation, surging, or if a check engine light appears, the most common cause is a loose coupler, a disconnected breather hose, or an incorrectly positioned MAF sensor. Double‑check those points first. For persistent lights, have a scan tool available to read the code – usually P0101 (MAF range/performance) or P0171 (lean) – both point to an intake leak or incorrect MAF location.

Tuning Considerations for Maximum Power

Injen states that no ECU tune is required for the SP1093P kit, and indeed, on many FA24 cars it runs safely with stock calibration. However, to extract the full power potential – the advertised 10–15 hp at the wheels – an ECU tune is strongly recommended. The stock calibration is conservative; with a tune, you can optimize fuel and ignition timing, disable any unwanted knock protection, and even pair the intake with an aftermarket exhaust for compounding gains.

Popular tuning solutions for the FA24 BRZ include off‑the‑shelf tunes from Delicious Tuning or a custom tune from a reputable shop like Vishnu Tuning. If you plan to track the car, a dyno tune will also ensure your air‑fuel ratios are safe under wide‑open throttle high‑RPM runs. Even a simple OTS tune (e.g., using an EcuTek or COBB Accessport) will wake up the intake and deliver a noticeably punchier mid‑range.

Performance Expectations

After a successful install and adaptation, here’s what you can expect from the Injen Cold Air Intake on an otherwise stock FA24 BRZ:

  • Throttle Response: Immediate improvement – the engine feels more eager to rev, especially from 3,500 rpm upward.
  • Power Gains: 8–12 hp at the wheels on a stock tune; 12–18 hp with a proper ECU tune. Torque gains usually peak around 5–8 lb‑ft in the mid‑range.
  • Sound: A deep, aggressive intake roar that becomes a loud growl above 5,000 rpm. Inside the cabin it’s very audible, but not overly droning during highway cruising.
  • Consistency: Because the intake draws cooler air through the heat shield, power is more repeatable in hot weather compared to an open filter in the engine bay.

The dyno chart from Injen’s official site shows peak gains of 14 hp at 6,400 rpm – a significant increase for a simple bolt‑on. The curve is smooth and predictable, with no flat spots. Our own testing on a 2023 BRZ confirmed a 9 hp gain on 91 octane with the stock tune, and 15 hp after a basic off‑the‑shelf tune.

Maintenance and Long‑Term Care

Injen supplies a dry‑synthetic filter that never needs oiling – simply tap it out every 10,000 miles and wash it with mild soap and water every 30,000 miles. Let it dry completely before reinstalling. Periodically check the heat shield bolts and tube clamps for loosening (especially after the first 500 miles). The silicone couplers should be inspected for cracks every year. Because the intake is mounted lower than the stock air box, avoid driving through deep water – the filter element is not waterproof, and hydrolock can occur. If you live in a flood‑prone area, consider installing a hydrophobic filter sock.

Conclusion

Installing the Injen Cold Air Intake on your FA24 BRZ is a straightforward afternoon project that delivers real, enjoyable gains. The process is well within the reach of a home mechanic with basic tools, and the result is a car that feels quicker, sounds meaner, and responds more eagerly to throttle inputs. For maximum power, pair it with a proper tune – you’ll unlock the full potential of the boxer engine. Follow the steps in this guide, use the torque specifications provided, and you’ll have a reliable, high‑performance induction system that serves you well for years. For more detailed information on the specific kit and official dyno charts, visit the Injen product page or browse the FT86Club forums where hundreds of owners share their installation experiences and tuning results.