The Genesis G70, especially the 3.3L twin-turbo V6 model, has become a favorite platform for enthusiasts looking for serious power without sacrificing daily drivability. The factory twin-scroll turbos deliver strong mid-range torque, but they plateau quickly once you push past 370 HP at the crank. The HKS GT II Turbo kit addresses this limitation by replacing the stock units with larger, more efficient compressors that flow significantly more air at higher boost levels.

With the HKS GT II setup, owners consistently report 380 to 420 HP at the wheels on pump gas, and well over 470 HP with ethanol blends and a proper tune. The kit is designed as a direct bolt-on replacement, meaning you can do the install in your home garage with basic tools if you follow the right sequence. This guide walks you through every step of the installation process, from prep work to the break-in procedure, so you can maximize performance and reliability.

Tools and Parts You Will Need

Before you begin, gather everything required for a smooth install. Running out for a missing gasket or tool mid-job can cost you hours. Here is a complete list of what you will need:

  • HKS GT II Turbo Kit — confirm your kit includes both turbochargers, wastegate actuators, and all required hardware
  • Metric socket and wrench set — 8mm through 19mm, including deep sockets and swivel adapters
  • Torque wrench capable of readings from 10 to 80 ft-lb
  • Set of new OEM gaskets — turbo-to-manifold, downpipe-to-turbo, and intake gaskets
  • Engine oil and coolant — use a high-quality synthetic 5W-30 for the G70 and approved OAT coolant
  • New oil feed and return lines — HKS kit typically replaces these, but confirm you have the correct AN fittings
  • Intercooler piping upgrade — the stock plastic end tanks can burst under increased boost, so consider a metal intercooler and hard pipes
  • Boost gauge and boost controller — optional but highly recommended to monitor and adjust boost pressure safely
  • Shop rags, catch pans, and safety glasses

Step 1: Prepare the Vehicle and Work Area

Park the G70 on a flat, level concrete surface. Chock both rear wheels to prevent any unintended movement. Disconnect the negative battery terminal and secure the cable away from the post. The G70 uses a smart alternator and sensitive electronics, so a dead short or accidental ground during turbo work can damage modules. Use a memory saver if you want to retain radio presets and learned transmission adaptives, but disconnecting the battery fully is the safer choice for the install.

Jack the front of the car up securely and place jack stands under the frame rails. Do not rely on the scissor jack provided with the vehicle. Remove the front under tray — there are roughly 16 fasteners holding it in place. With the tray gone, you have full access to the turbochargers, wastegates, and oil lines.

Step 2: Drain Fluids and Remove the Air Intake System

Drain the engine oil and coolant before removing any turbo components. This prevents spills and ensures a clean working environment. Remove the oil filler cap to speed up drainage. Once the oil is out, remove the coolant reservoir cap and drain the coolant from the radiator petcock.

Remove the complete factory intake system: the air box, intake tubes, and MAF sensor housing. Unplug the MAF sensor and set it aside carefully. Remove the turbo inlet pipes — these connect the air filter housing to each turbocharger. On the G70, the passenger-side inlet is relatively easy, but the driver-side sits behind the battery tray. Removing the battery and battery tray gives you the clearance needed.

Step 3: Remove the Factory Turbochargers

With the intakes removed, you can see both turbos clearly. Begin with the passenger-side unit because it has slightly more access room.

  • Disconnect the oil feed line from the top of the turbo using a line wrench. The banjo bolt can be tight, so apply penetrating oil if needed.
  • Disconnect the oil return line from the bottom of the turbo. Have a catch pan ready — residual oil will drain out.
  • Remove the coolant feed and return lines. Use a pinch-off tool on the rubber hoses to minimize coolant loss.
  • Unbolt the downpipe from the turbo outlet flange. There are three bolts; the lower one is difficult to reach, so use a swivel socket.
  • Unbolt the turbo from the exhaust manifold. There are four nuts securing the turbo to the manifold. Carefully wiggle the turbo free and pull it straight down and out of the engine bay.
  • Repeat the same process on the driver-side unit. The driver-side is tighter because of the steering shaft and brake booster lines, but it comes out with patience.

Note: Inspect the exhaust manifold studs while you have the turbos off. If any studs are bent or stripped, replace them now. A properly seated turbo prevents exhaust leaks and uneven boost.

Step 4: Preparing for the HKS GT II Installation

Cleaning the mounting surfaces is a critical step that many skip. Use a non-abrasive pad and brake cleaner to remove all carbon deposits from the exhaust manifold flanges and the oil return ports. Any debris left behind can restrict oil flow and cause premature turbo failure. Install the new gaskets provided with your HKS kit onto the manifold studs. Ensure the gaskets are oriented correctly — the metal side faces the manifold on most OEM-style replacements.

Step 5: Install the HKS GT II Turbochargers

This step is where the real transformation happens. The HKS GT II turbos are physically larger than the factory units, so careful positioning is required.

  • Lubricate the turbo bearings by pouring a small amount of clean engine oil into the oil feed port and spinning the compressor wheel by hand. This ensures the bearings are not dry at first startup.
  • Mount the turbo to the manifold. Slide the turbo onto the studs, install the locking nuts, and tighten them in a crisscross pattern. Torque to 18-22 ft-lb — do not overtighten.
  • Attach the oil return line using a new crush washer. The return line must slope downward continuously to avoid oil pooling in the turbo.
  • Connect the oil feed line. The HKS kit typically uses a braided stainless line with AN fittings. Route the line away from the exhaust manifold and tight against the engine block to avoid heat soak.
  • Reconnect the coolant lines. Use new O-rings at each connection. Torque the banjo bolts to 14 ft-lb.
  • Install the downpipe onto the new turbo outlet. Use the gasket supplied in the kit. The HKS outlet flange is slightly larger than OEM, so the downpipe may need a slight port match or a new downpipe optimized for the GT II.
  • Repeat for the second turbo. The driver-side unit mirrors the passenger side. Pay attention to wastegate actuator clearance — you may need to clock the actuator arm to avoid contact with the steering intermediate shaft.

Step 6: Upgrade the Intercooler and Piping

Stock G70 intercoolers are known to heat soak quickly when pushing over 370 HP. With the HKS GT II turbos producing higher outlet temperatures and pressure, a larger front-mount intercooler is a necessity rather than an option. Install a high-flow bar-and-plate intercooler with cast end tanks. Connect the system using 2.5-inch or 3-inch hard piping with silicone couplers and T-bolt clamps. The increased volume of the intercooler and piping will also slightly increase turbo lag, but the HKS GT II spools quickly enough that the trade-off is negligible.

Step 7: Reinstall the Intake System

With the turbos and intercooler in place, reconnect the intake system. Use the HKS or aftermarket intake pipes designed for the larger compressor inlet. Secure all couplers with clamps. Reinstall the MAF sensor, ensuring the orientation arrow points toward the turbo. Reinstall the battery tray and battery, reconnect the battery terminals, and torque the terminal bolts to 11 ft-lb.

Step 8: Refill Fluids and Bleed the Cooling System

Refill the engine with the recommended 5W-30 synthetic oil. The HKS GT II turbos hold more oil volume in their larger center sections, so check the dipstick after running the engine and top off as needed. Refill the cooling system with the correct OAT coolant mixed 50/50 with distilled water. Run the engine with the radiator cap off and the heater set to full hot to purge air pockets. Top off the coolant reservoir as the air escapes.

Step 9: Turbo Break-In Procedure

New turbochargers require a careful break-in to seat the bearings and seals. Start the engine and let it idle for 10 minutes. Do not rev the engine during this period. Check all connections for leaks — oil, coolant, and air. If you see a slight wisp of smoke from the exhaust, that is normal as machining oils burn off the new components. Let the engine cool completely after the initial idle. Then, start the engine again and warm it to operating temperature. Perform a series of gentle throttle applications, keeping boost under 7 PSI for the first 100 miles. Avoid sustained high-load runs until you reach at least 300 miles on the new turbos.

Step 10: ECU Tuning

You cannot run the HKS GT II turbos on the factory ECU calibration. The increased airflow requires a custom tune to adjust fueling, ignition timing, and boost targets. Use a reputable tuning solution for the G70 platform, such as a JB4 piggyback, a standalone ECU, or a flash tune from RAC Engineering or LAP3. A proper tune for 380+ HP should target an air-fuel ratio of 11.5:1 under full load and peak boost around 22-24 PSI on 93 octane, and up to 28 PSI on E85 with upgraded fuel injectors and a higher-flow low-pressure fuel pump.

Fuel system upgrades become mandatory at these power levels. The direct injection fuel pump on the G70 runs out of capacity around 420-440 HP. If you want to go beyond 380 HP reliably, you will need at minimum upgraded HPFP internals and a port injection auxiliary system. Many owners also upgrade the fuel lines and in-tank pump to support the volume required for E85 blends.

Step 11: Test Drive and Monitoring

With the tune loaded and the break-in miles completed, it is time for a thorough test drive. Start by driving gently through city traffic to verify drivability — the car should idle smoothly, not stumble off idle, and show no warning lights. Monitor the following parameters on a data logging app or boost gauge:

  • Peak boost pressure — should match your tuner's target
  • Oil pressure at idle and under load — should stay above 15 PSI at hot idle and above 50 PSI under acceleration
  • Exhaust gas temperature — keep EGT below 1600°F to avoid melting the turbine wheel or catalytic converters
  • Coolant temperature — should stay within the factory range of 195-205°F

Perform a single third-gear pull from 2500 RPM to 6500 RPM on an empty, safe road. Check the data log afterward for any knock retard, fuel trims that are out of range, or boost oscillations. If everything looks clean, the installation is successful.

Step 12: Routine Maintenance After the Upgrade

The HKS GT II turbos place higher thermal and mechanical stress on the engine. Shorten your oil change interval to every 3,000 miles using a full synthetic 5W-40 for added high-temperature protection. Inspect the turbo oil feed lines for cracking or hardening every 6 months. Change the spark plugs to a colder heat range (NGK 5758 gapped to 0.022 inches) to prevent pre-ignition. Keep your air filters clean — a clogged filter on a high-flow turbo setup can cause compressor surge and damage the blades.

Common Pitfalls and How to Avoid Them

  • Oil leaks at the return line. Always use a new gasket or O-ring and torque to spec. The return line is gravity-fed, so any leak is a steady drip.
  • Boost creep from the wastegate actuator. If boost climbs uncontrollably past redline, the factory wastegate actuator may not have enough force. Upgrade to a stronger HKS or Forge wastegate actuator with a higher spring rate.
  • Insufficient fuel pressure at high RPM. As noted earlier, the stock fuel system tops out around 420 HP at the crank. Log fuel pressure during your pulls and consult your tuner if pressure drops below 50 PSI.
  • Heat damage to nearby wiring. The HKS GT II turbine housing sits close to the starter motor wiring and the O2 sensor connectors. Wrap these connections in heat-reflective tape or DEI titanium wrap.

Realistic Power Expectations and Final Thoughts

With the HKS GT II turbo installation completed correctly and a quality tune, your G70 will produce roughly 380-410 WHP on 93 octane pump gas. On E85 with supporting fuel mods, the same setup can deliver 480-500 WHP. The powerband shifts higher in the RPM range compared to stock, but the mid-range torque surge is still impressive — expect peak torque around 3800-4200 RPM instead of the stock 2800 RPM. The car will pull hard to the 6800 RPM redline without running out of breath.

This setup is proven reliable when preventive maintenance and proper tuning are respected. The G70 chassis handles this power level well with upgraded tires and suspension components. Whether you plan to track the car, take it to drag days, or simply enjoy a faster daily commute, the HKS GT II turbo installation is one of the most effective modifications you can make. Take your time on the install, trust your tuner, and keep your data logs clean.

For more technical details, visit the official HKS GT II product page for specifications and compressor maps. If you are researching fueling upgrades, this guide to G70 fuel system upgrades is a helpful resource. For detailed tuning parameters, check out the community tuning thread on RaceDepartment.