Why Upgrade Your WRX Intake?

Upgrading the restrictive factory intake on your Subaru WRX is one of the highest-return modifications available. The stock air box is designed for sound deadening and cost efficiency, not performance. Replacing it with a Mishimoto cold air intake system reduces airflow restriction, lowers intake air temperatures, and dramatically improves the mechanical character of your car. You will hear the distinct spool of the turbocharger and the sharp release of the bypass valve like never before.

Mishimoto uses aerospace-grade 6061 aluminum with a wrinkle-black powder coat finish. Their kits are designed for the FA20 (2015-2021 VA chassis) and FA24 (2022+ VB chassis) WRX. When properly installed and paired with a calibration, these intakes deliver a measurable increase in horsepower and torque. The sealed heat shield design also mitigates heat soak during stop-and-go driving, which is a known weakness of the factory setup.

This guide walks you through the complete installation process, covering the tools you need, the removal of the factory components, and the fitment of your new Mishimoto intake. It also addresses tuning requirements and long-term maintenance to keep your WRX running at its peak.

Tools, Materials, and Safety

Before you put a wrench on anything, gather the correct tools and prepare your workspace. A clean, organized garage bay with good lighting will make the installation much smoother.

Tools Required

  • Socket Set: 10mm and 12mm sockets are standard for most intake hardware.
  • Ratchet and Extensions: A 3/8-inch drive ratchet with a 6-inch extension helps reach recessed bolts.
  • Flathead Screwdriver: Used for releasing MAF sensor locking tabs and loosening spring clamps.
  • Torque Wrench: Essential for tightening MAF sensor screws and intake tube clamps to specification.
  • Pick Set: Helps disconnect stubborn electrical connectors and vacuum lines.
  • Panel Clips Tool (Trim Tool): Useful for removing any plastic fasteners holding the engine bay covers.
  • Shop Towels and Safety Glasses: Keep your work area clean and protect your eyes from debris.

Safety and Preparation

Safety is the single most important part of any DIY installation. Follow these steps strictly to avoid injury or damage to your vehicle.

  • Park on a Level Surface: Engage the parking brake and chock the rear wheels.
  • Disconnect the Battery: Always disconnect the negative battery terminal before working on the intake system. This prevents the engine from accidentally starting and clears the ECU memory for the post-install idle relearn.
  • Engine must be Cool: If you have been driving, let the engine cool down completely. The turbocharger and surrounding metal components get hot enough to cause severe burns.
  • Read the Manual: Mishimoto includes a detailed instruction booklet. Read it cover to cover before starting. The specific steps for the VA chassis may differ slightly from the VB chassis.

Step 1: Removing the Factory Intake System

The factory intake consists of an air box, a snorkel duct, a resonator chamber, and a rubber intake tube connecting to the turbocharger inlet. Removing these components frees up space and allows you to install the new Mishimoto system.

Disconnecting the MAF Sensor and Hoses

The Mass Airflow (MAF) sensor is located on the intake tube between the air box and the turbo inlet. It is a sensitive component that must be handled carefully.

  1. Locate the MAF sensor connector on the intake tube.
  2. Press the locking tab down and pull the connector straight out. Do not pry on the sensor housing itself.
  3. Use a flathead screwdriver to gently pry the MAF sensor out of the factory intake tube. It is held in place by two small screws (usually Torx or Phillips). Keep these screws safe.
  4. Locate and disconnect the crank case ventilation hose (also known as the PCV or breather hose) that runs from the engine valve cover to the factory intake duct. A pick tool helps release these rubber hoses.

With the sensors and hoses detached, you can move on to removing the physical intake components.

Removing the Air Box and Snorkel

  1. Remove the Snorkel: The plastic snorkel runs from the front grille into the air box. It is held in by a few screws or push-pins. Remove it and set it aside.
  2. Unbolt the Air Box: The lower air box is secured to the chassis with a 10mm bolt and a few rubber grommets. Loosen the bolt holding the air box down.
  3. Loosen the Turbo Inlet Clamp: The intake tube connects to the turbocharger inlet via a large worm-gear or spring clamp. Loosen this clamp until the tube pulls free.
  4. Extract the Assembly: Pull the entire factory intake assembly (lower box, upper box, and intake tube) straight out of the engine bay. You may need to wiggle it past the radiator fan shroud.

Step 2: Installing the Mishimoto Cold Air Intake

With the factory clutter removed, you can see the turbo inlet clearly. Wipe down any oil or debris that may have accumulated near the turbo inlet before installing the new hardware.

Mounting the Heat Shield

The Mishimoto heat shield is a critical part of the kit. It creates a barrier between the air filter and the hot engine bay.

  • Position the aluminum heat shield into the mounting location. It usually sits on the frame rail near the headlight or uses a bracket attached to the chassis.
  • Hand-tighten the provided mounting bolts first, then torque them to specification using your torque wrench. An unsteady heat shield can cause rattles.
  • Ensure the silicone sealing strip (if included) sits flush against the hood when closed. This seals the intake from hot under-hood air.

Installing the Intake Tube and MAF Sensor

The intake tube connects the turbo inlet to the air filter. It is routed through the space where the factory air box sat.

  1. Position the Couplers: Slide the provided silicone couplers and T-bolt clamps loosely onto the Mishimoto aluminum tube. Do not tighten them yet.
  2. Connect to Turbo Inlet: Attach the coupler end to the turbocharger inlet. Tighten the clamp firmly. A boost leak here will cause poor idle and performance.
  3. Transfer the MAF Sensor: Install the MAF sensor into the designated slot on the Mishimoto tube. Lubricate the o-ring lightly with silicone grease for a smooth insertion and a positive seal. Ensure the sensor orientation matches the airflow arrow marked on the housing. Tighten the screws to the factory specification (typically 1.1 Nm).
  4. Reconnect the Sensor Connector: Plug the MAF sensor electrical connector back in until it clicks securely.

Connecting Crank Case Ventilation

Most Mishimoto WRX intake kits include a port for the PCV or breather hose.

  • Locate the barbed fitting on the Mishimoto intake tube.
  • Connect the factory crank case vent hose to this fitting. If the fit is loose, use the provided hose clamp to secure it.
  • If your kit requires a grommet or adapter for the valve cover connection, install it now. An unsealed vacuum leak here will cause rough running conditions.

Attaching the High-Flow Air Filter

The final step of the physical installation is securing the air filter.

  • Slide the high-flow cotton gauze filter onto the end of the intake tube.
  • Position the filter so it sits securely inside the heat shield, away from the radiator fan and wheel well liner.
  • Tighten the clamp enough to secure the filter but avoid crushing the intake tube. Over-tightening can deform the metal or filter housing.
  • Do a final check to ensure no wires, hoses, or cables are rubbing against the intake tube or the filter.

Step 3: Final Checks and First Start-Up

Before you reconnect the battery and start the engine, take ten minutes to verify every connection.

Verifying All Connections

  • Clamps: Re-tighten all T-bolt and worm-gear clamps. Make sure they are seated on the raised bead of the intake tube or turbo inlet.
  • MAF Sensor: Confirm the electrical connector is fully locked in and the wiring is not stretched.
  • Heat Shield: Give the heat shield a firm shake. It should be solid and not contact any moving parts.
  • Tools: Remove all tools, shop towels, and loose hardware from the engine bay.

Battery Reconnection and Idle Relearn

Disconnecting the battery resets the ECU learning tables. An idle relearn procedure is required to ensure the engine runs smoothly.

  1. Reconnect the negative battery terminal. Tighten the nut securely.
  2. Turn the ignition key to the "ON" position (do not start). Wait 5 seconds for the fuel pump to prime and the ECU to power up.
  3. Start the engine. It may run rough or idle high for the first few moments.
  4. Allow the engine to reach operating temperature. Let it idle for a full 10 minutes with all electrical accessories (radio, A/C, lights) turned off.
  5. After 10 minutes, turn the engine off completely. Wait 10 seconds, then restart the engine. The idle should stabilize to its normal smoothness.
  6. If the idle remains unstable, you may have a vacuum leak or a misaligned MAF sensor. Recheck all connections.

Performing a Boost Leak Check

A boost leak test is highly recommended after any intake installation. A simple way to check is to visually inspect all connections while a helper revs the engine gently. For a more thorough check, use a boost leak tester kit that pressurizes the intake system to 10-15 PSI. Any hissing sounds indicate a leak that must be addressed before driving hard.

Tuning Your WRX with a Cold Air Intake

This is the most critical point for modern Subaru WRX owners to understand. Installing a larger diameter intake tube significantly changes the MAF sensor voltage readings. The factory ECU map is not calibrated for this change.

Driving aggressively without proper calibration can lead to lean air-fuel ratios and engine knock. Mishimoto strongly recommends an ECU recalibration (tune) when installing their cold air intake. They have developed specific Off-The-Shelf (OTS) maps for use with an Accessport or OpenFlash Tablet. These maps optimize the fuel and timing curves to match the airflow characteristics of the intake.

When combined with a proper tune, the Mishimoto intake typically yields a gain of 10-20 wheel horsepower and a noticeable improvement in throttle response. Running the intake without a tune negates these benefits and risks engine damage. Always prioritize calibration as part of your intake upgrade budget.

Maintenance and Longevity

One of the advantages of the Mishimoto intake is the re-usable high-flow filter. Regular maintenance ensures the filter continues to flow air efficiently and protects your engine from debris.

  • Inspection Interval: Check the air filter every 5,000 miles or every oil change. A dirty filter will look dark and clogged.
  • Cleaning: Use a dedicated Mishimoto Filter Recharger Kit. Spray the cleaner onto the filter, let it soak for 10 minutes, and rinse with low-pressure water from the inside out. Let the filter dry completely before re-oiling.
  • Re-oiling: Apply the oil sparingly to the dry filter. A neon red color indicates the filter is saturated. Let the oil wick into the cotton gauze for an hour before reinstalling. Over-oiling can foul the MAF sensor.
  • Hardware Check: Every 10,000 miles, recheck the clamps and heat shield bolts. Thermal cycling can sometimes loosen hardware over time.

An additional benefit of the sealed Mishimoto heat shield is that it helps maintain lower IATs (Intake Air Temperatures) compared to open-element intakes or the factory box, which is beneficial for performance, especially during warmer months.

Frequently Asked Questions

Will installing this intake void my Subaru warranty?

A manufacturer cannot void a warranty simply because of an aftermarket part. However, if a failure is explicitly caused by the intake (such as debris ingress from a poorly maintained filter), the repair may not be covered by warranty. Using an OTS tune via Accessport will log your ECU history and could be grounds for a warranty claim denial regarding the powertrain.

How much louder is the intake compared to stock?

The intake generates significantly more induction noise. You will hear the turbo spooling and the bypass valve (BPV) recirculating air clearly inside the cabin. For many WRX owners, this is one of the most appealing aspects of the modification.

Do I need a tune for the 2022+ VB WRX?

Yes. The FA24 engine in the VB chassis is extremely sensitive to MAF changes. A tune is required to ensure safe air-fuel ratios and to prevent the ECU from pulling timing due to the altered airflow readings. Mishimoto provides specific calibration files for the VB chassis.

Can I install the intake by myself?

Yes. The installation is considered an intermediate-level DIY job. Having a friend helps when maneuvering the intake tube past the radiator fan, but the job can easily be completed by a single person in 2-3 hours with the correct tools.

Conclusion

Installing a Mishimoto cold air intake is a rewarding project that improves both the sound and performance of your Subaru WRX. The fit and finish of these kits are top-tier, and the engineering behind the heat shield is purpose-built for reducing heat soak. By following the steps outlined in this guide and respecting the vital requirement for an ECU calibration, you can confidently upgrade your intake system and enjoy a more responsive, powerful, and thrilling driving experience.