Introduction

Adding forced induction to your Subaru BRZ transforms its naturally aspirated character into a responsive, turbocharged powerhouse. The HKS GT II Turbo Kit is a well-engineered solution that pairs a high-quality GT II series turbocharger with a cast-iron exhaust manifold, efficient intercooler, and all necessary plumbing. This guide provides a comprehensive, step-by-step walkthrough of the entire installation, from component preparation to post-installation tuning. Whether you are an experienced DIY mechanic or a shop technician, these detailed instructions will help you achieve a reliable and high-performing turbo system.

Tools, Materials, and Safety Preparation

Required Tools

  • Socket set (metric, sizes 8mm–22mm) with extensions and universal joints
  • Combination wrenches (10mm, 12mm, 14mm, 17mm, 19mm)
  • Torque wrench (range 10–100 ft-lb)
  • Flathead and Phillips screwdrivers
  • Pliers (needle-nose, slip-joint, and snap-ring)
  • Jack and jack stands (or a lift)
  • Panel removal tools (for clips and trim)
  • Brake cleaner and shop rags
  • Drain pan and funnel
  • Vacuum/pressure tester (optional but helpful)

Supplied HKS GT II Kit Components

Before starting, verify your kit includes all parts listed in the HKS manual. Typical contents include the GT II turbocharger, cast-iron exhaust manifold, Tial-style wastegate (if applicable), intercooler core, piping kit, silicone hoses, clamps, oil feed and return lines, coolant lines, gaskets, and hardware. If any component is missing, contact your supplier before proceeding.

Consumables & Additional Parts

  • Engine oil – 5W-30 or recommended viscosity for turbo applications (approx. 5–6 quarts)
  • Coolant – Subaru Super Coolant or equivalent (approx. 2 gallons)
  • Oil catch can – strongly recommended to reduce oil residue in the intake tract
  • Boost gauge – to monitor turbo operation
  • Fresh gaskets for exhaust, intake, and oil pan (though kit includes them, spares are wise)
  • Thread locker (medium strength) for critical fasteners

Safety and Work Area

Park the BRZ on a level surface, let the engine cool completely (overnight is best), and disconnect the negative battery terminal. Have a fire extinguisher rated for Class B and C nearby. Work in a well-ventilated area; if using a lift, secure the vehicle with jack stands as a backup. Wear safety glasses and gloves when handling chemicals and hot components.

Removing Stock Components

Before the turbo can go in, the stock intake, exhaust manifold, and related parts must come out. Take your time and label connectors and hoses with masking tape to avoid confusion upon reinstallation.

Step 1: Remove the Engine Cover and Intake System

  • Unscrew the plastic engine cover (four 10mm bolts) and lift it off.
  • Loosen the clamps on the intake tube between the airbox and throttle body. Disconnect the MAF sensor connector and remove the entire intake assembly, including the airbox.
  • Unbolt the intake manifold support brackets (two 12mm bolts on each side) only if you plan to remove the manifold entirely; for this kit, you can leave the manifold in place but may need to disconnect the throttle cable and vacuum lines for access.

Step 2: Remove the Stock Exhaust Manifold

  • Raise the vehicle safely and support the front crossmember.
  • Disconnect the front oxygen sensor (O2) from the manifold wiring harness.
  • Remove the two nuts (14mm) securing the exhaust manifold to the engine block’s studs. There are 8 studs total; use a 12-point socket and penetrating oil if threads are stubborn.
  • Lower the manifold and the attached catalytic converter assembly. The manifold gasket will likely be destroyed; discard it and clean the block surface with a scraper and brake cleaner.

Step 3: Remove Additional Interfering Components

  • If your BRZ has an aftermarket header or unequal-length manifold, that must also come off. For stock, just the primary header.
  • Unbolt the heat shields around the exhaust manifold (10mm bolts).
  • Disconnect the lower oxygen sensor from the downpipe if still attached. Label the sensor wires.
  • Remove the starter motor (two 14mm bolts) to allow easier access to the rear studs of the manifold – this is often needed for the HKS manifold installation as well.
  • Set aside all removed hardware; you will reuse some of it for the turbo kit.

Installing the HKS GT II Turbo Manifold and Turbocharger

With the engine bay cleared, you can now install the HKS components. Work systematically to avoid cross-threading or misaligning exhaust flanges.

Attach the New Turbo Manifold

  • Apply a thin coat of copper anti-seize to the block studs (new studs are provided in the kit; use them if supplied).
  • Position the new gasket over the studs, ensuring the correct orientation (the gasket is embossed to show “exhaust side” or has a clear top/bottom indicator).
  • Place the HKS cast-iron manifold over the studs. Hand-tighten the nuts evenly.
  • Torque the manifold nuts in a crosshatch pattern to 28 ft-lb (38 Nm) in stages: first to 15 ft-lb, then to final torque. Recheck after 10 minutes of engine operation.

Mount the GT II Turbocharger

The HKS GT II turbo mounts directly to the manifold. Ensure the wastegate actuator arm is free to move and the oil drain port is oriented correctly (pointing downward).

  • Install the turbo-to-manifold gasket (supplied) onto the manifold flange.
  • Carefully position the turbocharger onto the flange. Use new locking nuts (typically M10) and torque to 35 ft-lb (47 Nm).
  • Connect the wastegate actuator to the turbo center housing using the provided bracket. Adjust the actuator rod to achieve the recommended preload (check the HKS manual for your specific turbo model).
  • If your kit includes an external wastegate (Tial or equivalent), mount it on the manifold’s designated flange using the supplied gasket and springs. Use thread locker on the mounting bolts.

Install the Downpipe and Exhaust System

Use the HKS downpipe (or fabricate one if not included) to connect the turbo outlet to the existing mid-pipe. Apply high-temperature anti-seize to the V-band clamp if used, or standard exhaust gaskets for bolt-type flanges. Torque the downpipe-to-turbo bolts to 30 ft-lb (40 Nm). Reattach the lower O2 sensor to the downpipe bung.

Intercooler and Charge Air Piping

Most HKS GT II kits for the BRZ include a front-mount intercooler (FMIC) that requires removing the lower grille and crash bar support. Check your specific kit instructions; some use a smaller air-to-air intercooler that fits behind the bumper cover without cutting.

Mounting the Intercooler

  • Remove the front bumper cover (six 10mm bolts across the top, two push-clips inside the wheel wells, and the under-tray screws).
  • Detach the foam impact absorber and remove the crash bar if required (four 18mm bolts). Some kits allow the intercooler to sit behind the crash bar without removal.
  • Position the intercooler core and attach the provided mounting brackets. Ensure the inlet and outlet are facing the driver side (typical routing). Tighten bolts to 15 ft-lb.
  • Reinstall the crash bar and bumper cover, trimming the plastic grille as needed for the intercooler’s core thickness.

Running the Charge Pipes

  • Connect the turbo compressor outlet (usually a 2-inch silicone hose with T-bolt clamp) to the intercooler’s driver-side inlet.
  • Route the hot-side pipe from the turbo to the intercooler, avoiding the fan shroud and upper radiator hose.
  • From the passenger-side intercooler outlet, run the cold-side pipe to the throttle body. Use the provided silicone coupler to connect to the throttle body flange. Secure all clamps to 6–8 Nm (finger-tight plus a quarter turn with a screwdriver).
  • Install a blow-off valve (BOV) if included in the kit; typically it mounts on the cold-side pipe near the throttle body. Connect the vacuum reference line to a manifold vacuum source.

Oil and Coolant Line Connections

Proper lubrication and cooling are critical for turbo longevity. Follow these steps precisely to prevent oil starvation, leaks, or overheating.

Oil Feed

  • Locate the oil feed port on the turbo housing (typically a banjo bolt fitting). The kit includes a -3AN or -4AN braided stainless line.
  • On the engine block, you can tap the main oil gallery or use a sandwich plate between the oil filter and block. The HKS kit usually provides a bolt-on oil feed adapter that replaces the oil pressure sensor location (behind the intake manifold). If so, install the adapter with Teflon tape and then attach the feed line.
  • Route the feed line away from the exhaust manifold; use heat sleeve protection. Connect to the turbo banjo bolt with two copper washers (one on each side of the fitting) and torque to 18 ft-lb (24 Nm).

Oil Return

  • The oil return line (larger -10AN or -12AN) must gravity-drain into the oil pan. The kit includes a welded bung that replaces the stock oil drain plug or is welded onto the pan.
  • Remove the oil pan (or drill and tap if you have the tools) to install the return bung. Many prefer to drop the pan, clean it, and weld the bung on the side above the oil level. Follow HKS instructions – some kits use a self-tapping fitting into the pan’s pre-drilled indent.
  • Connect the return line to the turbo with a silicone 90-degree hose and constant-tension clamps. Ensure the line has a continuous downward slope with no sags or kinks.

Coolant Lines

  • The water-cooled center housing of the GT II requires two coolant lines: one from a pressurized coolant source (e.g., heater hose T-fitting) and a return to the radiator or coolant reservoir.
  • Use the supplied barb fittings and silicone hose. Attach the inlet line to the turbo nipple, and the return line to the other nipple. Use spring-style clamps to avoid over-tightening.
  • Bleed the cooling system after installation: fill with Subaru coolant, run the engine with the heater on full, and rev periodically to purge air pockets.

Vacuum Lines, Electrical Connections, and Boost Control

A clean vacuum routing ensures accurate boost control and consistent idle.

  • Connect the wastegate actuator to a boost source. For a standard setup, tee into a line from the compressor outlet or intake manifold. Some kits use an electronic boost controller; wire it per the manufacturer’s instructions.
  • Install an aftermarket boost gauge; daisy-chain the signal line from the vacuum source (e.g., a Tee at the brake booster line).
  • Reinstall the intake system: Attach the HKS intake pipe (often with an integrated MAF housing) to the turbo inlet. Secure the MAF sensor and ensure the filter is clear of obstacles.
  • Reconnect the battery negative terminal and inspect all harness routing – keep wires away from heat sources and moving parts.

Final Assembly and Pre-Start Checks

Before turning the key, methodically inspect every connection.

  • Torque all exhaust bolts again – especially the manifold-to-head bolts – after thermal cycling (but before first start if you can access them).
  • Check intercooler pipe clamps for tightness. Confirm there is no contact with the hood, fan shroud, or radiator core.
  • Verify oil feed and return lines are not kinked. Crank the engine with the fuel pump relay disabled (remove the ECU fuse or disconnect the injectors) for 10 seconds to prime the oil system. Recheck for oil leaks at the turbo feed.
  • Top off oil and coolant. Fill the catch can with a small amount of oil if it’s empty to pre-lubricate the seals.
  • Install the boost gauge sensor and run the wiring to the cabin. Secure all lines with zip ties as needed.

Start-Up, Break-In, and Testing

Start the engine and let it idle. Listen for unusual noises – a faint scuff from the turbo is normal on first oil fill; it should disappear within seconds. Check for exhaust leaks by feeling around gaskets (use a glove).

  • Let the engine reach operating temperature. Verify that coolant temperature stabilizes and the oil pressure gauge reads within normal range.
  • Take a short test drive, staying below 3,000 RPM and avoiding boost. This allows the turbo seals and gaskets to settle.
  • After 20 miles of gentle driving, re-torque the exhaust manifold nuts and check for loose hardware. Inspect all fluid levels.
  • Gradually increase engine speed to 4,000 RPM over the next 100 miles, still refraining from sustained boost. Then perform several moderate acceleration runs – monitor the boost gauge to ensure it stays within the kit’s target (typically 6–8 psi for standard wastegate spring).

If you encounter boost creep, surging, or erratic idle, consult a professional tuner before pushing the engine harder.

ECU Tuning and Calibration

A turbo kit changes the engine’s airflow and fuel requirements dramatically. Even at low boost, the stock ECU will pull timing and run dangerously lean without a proper tune. Never drive the car in boost without a revised calibration.

Options for Tuning

  • OpenFlash Tablet – a popular DIY route with pre-loaded maps for HKS kits (requires a tablet and custom tune from a reputable provider).
  • Ecumaster EMU or Haltech Elite – standalone ECUs with professional wiring and mapping for maximum performance and safety.
  • ECUtek – reflash of the stock ECU, widely used for BRZ turbo setups. Many tuning shops offer remote calibration via email.

Regardless of the platform, the tuner will adjust fuel tables, ignition timing, and boost control strategy. Expect to spend several hours on a dyno or with a wideband O2 sensor to achieve a safe air/fuel ratio (11.5–12.0:1 under boost) and manage knock. Visit the official HKS website for recommended tuners or contact them directly for calibrations. For community experiences, check the FT86 Club forced induction forum. Many users pair this kit with a Delicious Tuning Flex Fuel kit for maximum power – Delicious Tuning offers specific tunes for the HKS GT II.

Maintenance and Longevity Tips

  • Change engine oil every 3,000 miles or 3 months, whichever comes first. Use a high-quality synthetic oil (e.g., Motul 300V or Amsoil Signature Series).
  • Inspect the oil return line for signs of carbon build-up or blockage every 10,000 miles.
  • Clean the intercooler fin pack annually with low-pressure water and a soft brush.
  • Replace the spark plugs with a colder heat range (one step colder: NGK LFR7AIX) at each oil change interval to reduce knock risk.
  • Keep the catch can emptied every 1,000 miles to prevent oil from contaminating the intake system.

Conclusion

Installing the HKS GT II Turbo Kit on your Subaru BRZ is a rewarding project that delivers a substantial performance increase when properly executed. By following this detailed guide – removing stock components carefully, mounting the turbo manifold and intercooler precisely, connecting oil and coolant lines without error, and securing a professional tune – your BRZ will gain reliable boost and enhanced drivability. Remember that patience during the break-in period and diligent maintenance are the keys to long-term turbocharger life. With the right preparation and attention to detail, you can enjoy a turbocharged BRZ that performs as impressively as it sounds.