Why Upgrade to the APS 600H Intercooler on Your WRX?

The Subaru WRX is a turbocharged platform that thrives on cooler intake air temperatures. The factory intercooler, while adequate for stock power levels, becomes a significant bottleneck as boost pressures and airflow increase. The APS 600H intercooler is a direct-fit, bar-and-plate upgrade designed specifically for GD and GG chassis WRX models (2002–2007). Its larger core volume, improved fin density, and cast end tanks provide substantially lower pressure drop and more consistent charge air cooling under sustained boost.

Installing the APS 600H not only reduces intake air temperatures (IATs) by 20–40°F in many cases, but also improves throttle response and engine safety margins. This guide walks you through the complete installation process with expanded details, torque specifications, and pro tips to ensure a leak-free, reliable setup. Always refer to the official APS website for the latest kit components and fitment notes.

Tools and Materials Needed

Having the correct tools on hand before you begin prevents frustration and damage. Below is a comprehensive list, including optional items that can make the job easier.

Essential Tools

  • Metric socket set (8mm, 10mm, 12mm, 14mm) – the intercooler mounting bolts are typically 12mm; bumper clips and screws are 8mm and 10mm.
  • Combination wrench set (10mm, 12mm, 14mm) – useful for accessing tight hose clamp locations.
  • Flathead and Phillips screwdrivers – for releasing factory hose clamps and plastic trim clips.
  • Torque wrench (5–50 ft-lb range) – critical for tightening intercooler mounting bolts and turbo outlet bolts to factory specifications.
  • Trim panel removal tool – helps pop bumper clips without breaking them.
  • Heat-resistant gloves – the intercooler pipes and end tanks can get extremely hot after even a short drive.
  • Safety glasses – protect your eyes from debris, coolant, or spring‑loaded hose clamps.
  • Wire cutters or side cutters – for cutting zip ties and removing old hose clamps.
  • Shop rags or towels – to catch small amounts of coolant that may spill when disconnecting hoses.
  • Small mirror and flashlight – for inspecting turbo outlet connections from underneath.
  • Dielectric grease – apply to electrical connectors before reconnecting fog light wiring.
  • Anti-seize compound – prevents bolt seizure in aluminum threads (use sparingly on intercooler bracket bolts).
  • Coolant additive (optional) – if you accidentally lose significant coolant, have the correct Subaru Super Coolant or equivalent on hand.

Preparation Steps

Proper preparation ensures a smooth installation. Park the vehicle on a level surface and allow the engine to cool completely – the intercooler sits directly above the turbo and exhaust manifold, and burns are a real risk.

Disconnect the Battery

Use a 10mm wrench to loosen the negative terminal bolt, then move the cable away from the battery post and secure it so it cannot accidentally make contact. This eliminates the chance of shorting the ECU or triggering a check engine light while unplugging sensors.

Remove the Front Bumper

Start by removing the plastic push‑pins and screws securing the top of the bumper cover to the radiator core support. There are typically three screws at the top (10mm) and two more inside each wheel well (usually Phillips-head or 10mm). Use a trim tool to release the push‑pins. Carefully pull the bumper outward from the fender edges, disconnecting any fog light or turn signal harness connectors. Rest the bumper on a padded surface to avoid scratching the paint. For detailed bumper removal, check community guides on IWSTI.

Remove the Stock Intercooler

The factory intercooler is mounted on two brackets at the sides and has a rubber Y‑pipe connecting the turbo outlet to the intercooler inlet. Follow these steps:

  1. Loosen the clamps on the Y‑pipe using a flathead screwdriver or 8mm socket – note the orientation of the clamps for reinstallation.
  2. Disconnect the breather hose from the driver‑side intercooler pipe (usually a 5/8" hose).
  3. Remove the two 12mm bolts securing the intercooler brackets to the chassis.
  4. Lift the intercooler upward and forward to disengage the two lower rubber mounts. Remove the Y‑pipe from the turbo outlet.
  5. Inspect the old intercooler for any debris or oil residue – this is a good opportunity to clean the intake path.

Installing the APS 600H Intercooler

Before you begin, unpack the APS 600H kit and verify all components: intercooler core, upper and lower silicone hoses, T‑bolt clamps, mounting brackets (for GD/GG chassis), and any specific bolts or spacers. If your kit is missing parts, contact APS or your retailer before proceeding.

Prepare the New Intercooler and Hoses

Inspect the APS core for any shipping damage (dented fins, cracked end tanks). The bar‑and‑plate construction is very robust but should still be checked. Apply a thin film of silicone spray or soapy water to the inside of the silicone hoses – this helps them slide onto the intercooler and turbo outlet without tearing. Do not use oil‑based lubricants that could damage the silicone.

Position and Secure the Intercooler

Place the APS intercooler into the engine bay, aligning the mounting brackets with the factory locations. The APS kit typically uses modified brackets that position the intercooler slightly lower and farther forward than stock for better airflow. Finger‑start the mounting bolts, then tighten them evenly to 9–12 ft‑lb (12–16 Nm). Over‑tightening can strip the aluminum threads in the core.

Turbo Outlet Connection

Slide the supplied 2.5” silicone hose onto the turbo outlet (the compressor housing). The APS kit may require a different orientation than the stock Y‑pipe – pay attention to the hose routing to avoid kinks. Secure with a T‑bolt clamp, orienting the bolt head for easy access. Torque T‑bolt clamps to 5–7 ft‑lb (6.8–9.5 Nm) – they crush the hose evenly without damaging the silicone.

Throttle Body and Bypass Valve Connections

The APS intercooler uses a larger diameter outlet to the throttle body than stock. Connect the provided silicone hose from the intercooler outlet to the throttle body inlet. If your WRX uses a factory bypass valve (BPV), you may need to reuse the stock hose or the supplied reducer – check fitment. Use T‑bolt clamps on all connections. Tighten gently to avoid distorting the silicone.

Breather and Vacuum Lines

Reconnect the driver‑side breather hose (crankcase vent) to the barb on the APS intercooler pipe. Some kits include a dedicated fitting; if using the factory hose, ensure the rubber is not cracked. For the bypass valve vacuum line, use a zip tie to secure it – boost leaks at this connection cause idle roughness.

Reassembly Steps

Reattach the Front Bumper

Before reinstalling the bumper, verify that all intercooler hoses do not contact the front core support or bumper beam. Adjust the intercooler position if necessary – you want at least 1/4” clearance to prevent rubbing through the hoses over time. Connect the fog light/sensor wiring, then carefully align the bumper cover and press the push‑pins and screws back in place. Tighten the wheel well bolts last.

Reconnect the Battery and Test Electricals

Reattach the negative battery terminal and tighten to 5–7 ft‑lb. Turn the ignition to the “ON” position without starting the engine. Check that all lights, turn signals, and fog lights (if equipped) function correctly. If you disconnected any other wiring, verify the ECU and MAF sensor harnesses are secure.

Final Checks and First Start

Perform a thorough visual inspection:

  • All hose clamps are snug and not biting into the silicone.
  • The intercooler is secure and does not rattle.
  • The turbo outlet hose is not kinked or contacting the fan shroud.
  • Breather hoses are connected and free of cracks.

Start the engine and let it idle. Listen for any whistling or hissing noises – these indicate boost leaks. Rev the engine gently to 2500–3000 RPM while watching the boost gauge (if installed). A small puff of smoke from the exhaust is normal as residual oil burns off. After the engine reaches operating temperature, shut it off and re‑torque all hose clamps – silicone hoses relax slightly as they heat cycle.

Finally, take a short test drive (3–5 miles) with varying RPM and light boost. Check again for leaks and recheck intercooler bolt torque after the drive. Monitor intake air temperatures via an OBD2 scanner if available – you should see noticeably cooler IATs compared to stock, especially during repeated pulls.

Post‑Installation Tuning and Maintenance

The APS 600H intercooler flows significantly more air than the factory unit. While it is a “bolt‑on” upgrade, your WRX’s ECU may need recalibration to take full advantage of the improved cooling. If you are still running the stock turbo and fuel system, the intercooler alone will not require a tune, but a custom tune (or off‑the‑shelf map for your specific mods) can safely increase boost and ignition timing. Consult a professional tuner or resources like Cobb Tuning for access to the Accessport platform if you are not already tuned.

Maintenance is straightforward: periodically inspect the front of the intercooler core for bug buildup, road debris, or bent fins. Use a fin comb and gentle water wash (avoid pressure washing directly on the fins) to keep airflow unrestricted. Also check the condition of silicone hoses every 12–18 months – they should remain supple and free of abrasion marks.

Common Installation Pitfalls to Avoid

  • Over‑tightening clamp bolts – this cuts into the silicone hoses and causes premature failure. Use a torque wrench or tighten by feel: when the T‑bolt head just starts to compress the hose against the metal nipple, stop.
  • Misaligned mounting brackets – the APS 600H is specific to left‑hand drive and right‑hand drive variants. Verify you have the correct bracket orientation before tightening.
  • Forgetting to remove the intercooler shipping plug – some kits include a plastic plug in the outlet to prevent debris from entering. Remove it before connecting hoses.
  • Leaving the Y‑pipe support bracket loose – the weld bracket on the intercooler should not rest on the engine crossmember. Use the provided rubber isolator if included.
  • Skipping the breather hose reconnection – an open crankcase vent causes idle surging and a rich condition. Double‑check that it’s securely attached.

Conclusion

Installing the APS 600H intercooler on your WRX is a rewarding upgrade that provides measurable gains in intake efficiency and engine safety. With the expanded steps above, you can confidently complete the installation in an afternoon and enjoy cooler charge air for years to come. Always double‑check your work against the official APS installation instructions for your specific kit revision, and do not hesitate to consult WRX forums for chassis‑specific tips. A properly installed intercooler not only supports higher power levels but also extends the life of your turbo and engine by reducing thermal stress.