Understanding the HKS GTII Turbo Upgrade for the Evo VIII

The Mitsubishi Lancer Evolution VIII is already a formidable machine from the factory, with its 4G63 engine producing approximately 280 horsepower. However, serious enthusiasts know that this platform has substantial untapped potential. The HKS GTII turbocharger represents one of the most well-engineered bolt-on upgrades available, offering a proven path to 400+ horsepower while maintaining the drivability and responsiveness that make the Evo VIII such a rewarding car to drive.

Unlike budget turbo upgrades that may cut corners on materials or turbine geometry, the HKS GTII benefits from HKS's decades of turbocharging experience and their work in motorsport. The result is a turbocharger that spools quickly, moves substantial air, and withstands the thermal and mechanical stresses of high-boost operation. For Evo VIII owners who want a significant performance jump without stepping up to a full race-spec turbocharger, the GTII sits in a sweet spot that balances power potential with daily usability.

What Makes the HKS GTII Different from Stock

The factory Evo VIII turbocharger is a well-designed unit for its intended power level, but it reaches its flow ceiling relatively quickly. The HKS GTII uses a larger compressor wheel with advanced blade geometry that can move more air at higher pressure ratios. This directly translates to the ability to make more power, whether you are running pump gas or ethanol blends.

On the turbine side, the GTII features an enlarged turbine housing and wheel that reduces exhaust backpressure. Lower backpressure means the engine doesn't have to work as hard to push exhaust gases out, which improves volumetric efficiency and allows the engine to produce more power at the same boost level. The wastegate design is also improved over stock, offering better boost control and reducing the tendency for boost creep that can plague modified Evos.

A key engineering advantage of the HKS GTII is the bearing system. HKS uses a high-quality journal bearing design with precision oil clearances that provide quick oil flow at startup while maintaining durability at high shaft speeds. This contributes to the turbo's reputation for reliability even under sustained high-load operation.

Installation Process: A Step by Step Guide

Installing the HKS GTII turbocharger on an Evo VIII is not a casual weekend job for a beginner, but it is well within the capabilities of a competent home mechanic with proper tools and workspace. The process typically takes between 6 and 10 hours depending on experience level and whether any supporting modifications are being installed simultaneously.

Preparation and Parts Gathering

Before starting the physical installation, you need to ensure you have all necessary components on hand. Beyond the turbocharger itself, you will need new gaskets for the exhaust manifold, turbo to manifold connection, turbo to downpipe connection, and oil feed and return lines. Many experienced builders recommend replacing the oil feed line with a braided stainless steel unit and upgrading the oil drain line to ensure proper flow.

You should also have fresh coolant, engine oil, and a new oil filter ready. An OEM or high-quality aftermarket oil pump is recommended if your car has significant mileage. Additional parts that often make sense to replace during a turbo upgrade include the exhaust manifold studs and nuts, which can corrode and break during removal, and the water lines that connect to the turbo.

Disconnecting and Removing the Factory Turbo

Begin by disconnecting the battery to eliminate any risk of short circuits or accidental fuel pump operation. Drain the engine coolant and engine oil to minimize mess when lines are disconnected. Remove the intake piping, intercooler piping, and air filter assembly to gain access to the turbo area.

Unbolt the downpipe from the turbo and the exhaust system. You may need to support the exhaust system with a jack or stand. Remove the heat shields covering the turbo and exhaust manifold. The stock turbo is held in place by the exhaust manifold bolts, the oil feed line, the oil return line, and the coolant lines. Work systematically, labeling each connection as you go, and take photos to aid reassembly.

Once all bolts and lines are disconnected, the stock turbo and exhaust manifold can be removed as an assembly. This is easier than trying to separate them on the car. Inspect the exhaust manifold for cracks or warpage while it is off the car.

Installing the HKS GTII Turbo

Before bolting on the new turbo, thoroughly clean the exhaust manifold mating surface and the cylinder head surface. Install new studs if needed and apply anti-seize compound to the threads. Carefully place the HKS GTII onto the manifold, using a new gasket. Tighten the bolts in a crisscross pattern to the manufacturer's torque specification.

Install the new oil feed line, ensuring it is routed away from hot surfaces and not kinked. The oil return line requires particular attention: it must have a continuous downward slope from the turbo to the oil pan to ensure gravity drainage. Any restrictions or dips in the return line can cause oil to back up into the turbo center housing, leading to seal failure.

Connect the coolant lines, using new crush washers or O-rings as supplied by HKS. Reinstall the downpipe with a fresh gasket. Before connecting the intake and intercooler piping, verify that all turbo connections are secure and that the wastegate actuator arm is properly attached to the wastegate flapper.

Post-Installation Checks

Refill the engine with oil and coolant. Before starting the engine, you should prime the turbo with oil. The easiest method is to disable the ignition and crank the engine for 10 to 15 seconds in short bursts until oil pressure registers on the gauge. This ensures the turbo bearing receives oil before it sees engine load.

Start the engine and allow it to idle, checking for oil leaks at every connection, coolant leaks, and exhaust leaks. Listen for any unusual noises from the turbocharger. A small amount of smoke from the exhaust during the first startup is normal as assembly lubricants and any residual oil in the system burn off.

Perform a thorough boost leak test on the entire intake system, including the intercooler and all piping. A single boost leak at the turbo outlet or intercooler end tank can cause drivability issues and limit power output.

Tuning Requirements for the HKS GTII Turbo

Installing the HKS GTII turbo without proper tuning is a recipe for engine damage. The increased airflow will push the stock fuel system beyond its safe limits, and the factory ECU cannot compensate for the dramatically different airflow characteristics of the larger turbo.

Fuel System Upgrades

At a minimum, you will need larger fuel injectors and a higher-flowing fuel pump. For power levels up to 400 horsepower, 750cc to 1000cc injectors are typically sufficient, paired with a Walbro 255 lph or equivalent fuel pump. If you plan to run E85 or push beyond 450 horsepower, 1200cc or larger injectors and a brushless fuel pump are strongly recommended.

Fuel pressure regulation also becomes important at higher boost levels. A quality aftermarket fuel pressure regulator ensures consistent fuel delivery across the entire RPM range, preventing lean conditions that can lead to detonation and engine failure.

ECU Tuning and Engine Management

The stock Evo VIII ECU can be reflashed by a reputable tuner, and this is the most common route for GTII installations. Several reputable tuning solutions exist, including open-source options and commercial reflashing tools. A standalone engine management system offers greater flexibility and data logging capability, but for most street-driven cars, a well-executed reflash is more than adequate.

During the tuning process, the tuner will adjust fuel maps to target air-fuel ratios in the low 11s under boost for pump gas, or mid 11s for E85. Ignition timing maps are adjusted to find the maximum advance before knock occurs, often reducing timing in the mid-range on pump gas to account for the increased cylinder pressure from the larger turbo.

Boost control strategy should also be calibrated. The HKS GTII will typically be run between 20 and 28 psi on pump gas, and up to 32 psi or more on race fuel or ethanol. The wastegate actuator pressure and boost controller settings must be dialed in to match the turbo's flow characteristics and the engine's capabilities.

Essential Tuning Tools

A wideband oxygen sensor is non-negotiable for tuning. This device provides real-time air-fuel ratio data that is essential for both the initial calibration and ongoing monitoring. Data logging software allows the tuner to capture RPM, boost, air-fuel ratio, ignition timing, and knock sensor activity during pulls, forming the basis for tuning decisions.

Dyno time is highly recommended, though not strictly required. A dyno provides consistent, repeatable loading conditions and allows the tuner to safely evaluate the engine's response at wide-open throttle without the risks of street tuning.

Supporting Modifications That Unlock Peak Power

The HKS GTII turbo can flow enough air to support over 450 horsepower, but the rest of the engine's systems must be capable of handling that airflow. Several supporting modifications make a significant difference to the final power output and the overall reliability of the setup.

Exhaust System

An upgraded turbo-downpipe and cat-back exhaust system reduce backpressure and allow the turbo to spool more freely. A 3-inch diameter exhaust from the turbo back is the standard recommendation for the GTII setup. A high-flow catalytic converter can be retained for street legality if desired, but a full catless system offers the best flow.

Intake and Intercooler

The stock air box and intake piping are restrictive once the turbo is flowing more air. A cold air intake with a large conical filter and smooth tubing reduces inlet restriction. An upgraded front-mount intercooler with larger core volume and efficient end tanks reduces intake air temperatures, which directly increases knock resistance and power potential.

Engine Internals and Cooling

The 4G63 engine has strong internals from the factory, but at power levels exceeding 450 horsepower, forged pistons and connecting rods become a wise investment. The stock cooling system should be upgraded with a larger radiator and possibly oil cooler if you intend to track the car or drive in hot climates.

Power Potential and Real-World Dyno Results

With the HKS GTII turbo and proper supporting modifications, Evo VIII owners can expect significant power gains. On pump gas (93 octane) with 22 to 24 psi of boost, the GTII typically produces between 370 and 400 wheel horsepower. This represents a gain of roughly 70 to 100 horsepower over a stock Evo VIII at the wheels.

When running E85 fuel with boost increased to 28 to 30 psi, power levels rise to the 420 to 450 wheel horsepower range. The torque curve is particularly impressive, with peak torque often exceeding 380 lb-ft and arriving earlier than many competing turbo upgrades.

With race fuel, a fully built engine, and aggressive boost levels, some setups have pushed beyond 500 wheel horsepower, but this requires extensive supporting modifications and is not recommended for street-driven cars that must balance reliability and longevity.

For comparison, a stock Evo VIII typically dynos at around 230 to 250 wheel horsepower, depending on the dyno and correction factor. A well-executed HKS GTII setup on pump gas essentially doubles the power at the wheels, which transforms the driving experience.

Drivability and Spool Characteristics

The HKS GTII is praised for its spool characteristics. Full boost arrives by approximately 3500 to 3800 RPM, depending on exhaust configuration and boost level. This is only about 300 to 500 RPM later than the stock turbo, but the difference in power delivery is substantial. The GTII continues pulling hard past 7000 RPM, where the stock turbo begins to run out of breath.

This broader power band means the GTII-equipped Evo VIII is more flexible in daily driving. You do not need to rev the engine to 6000 RPM to make a pass on the highway; the mid-range torque is strong enough to deliver satisfying acceleration from any RPM above 3000.

Common Issues and Reliability Considerations

No turbo upgrade is without potential pitfalls. The HKS GTII is generally reliable when installed and tuned correctly, but there are several areas that require attention.

Oil supply and drainage. As mentioned earlier, the oil return line is critical. Any restriction here will cause oil to leak past the turbo seals, resulting in blue smoke from the exhaust. Use the largest diameter oil return line that fits and verify its routing carefully.

Boost control. The GTII's wastegate actuator must be properly set. If the actuator is too weak, boost will spike uncontrollably. If it is too stiff, boost will be limited and spool will suffer. An aftermarket electronic boost controller is highly recommended for precise boost management.

Heat management. The increased power output generates more heat in the engine bay. Turbo blankets, heat wrap on downpipes, and proper heat shielding for the intake system help keep temperatures under control. Overheating the intake air can cause detonation and limit power gain.

Engine longevity. With power levels above 400 wheel horsepower, the stock 4G63 head gasket and head studs become a weak point. ARP head studs and a quality multi-layer steel head gasket are recommended for any GTII build, especially if you plan to use high boost levels or track the car.

Comparing the HKS GTII to Other Evo VIII Turbo Upgrades

The HKS GTII competes with several other popular turbo upgrades for the Evo VIII, including the FP Green, the Garrett GT3076R-based kits, and the MAP EF3. Each has its own characteristics that suit different priorities.

The FP Green is known for its quick spool and strong mid-range, making it excellent for street driving and autocross. The GT3076R offers slightly more top-end power but spools later. The MAP EF3 is a direct bolt-on that offers good performance at a lower cost. The HKS GTII distinguishes itself with its build quality, bearing design, and the reputation of the HKS brand for reliability and consistency.

Conclusion

The HKS GTII turbo upgrade for the Mitsubishi Lancer Evolution VIII remains one of the most well-regarded modifications in the Evo community for good reason. It delivers a substantial and predictable power increase, spools quickly for its size, and is built to a standard that supports long-term reliability when installed and tuned correctly.

For the owner who wants a car that is significantly faster than stock but still comfortable and reliable for daily driving, the GTII represents an excellent investment. The key is to approach the build holistically: allocate budget not just for the turbo itself, but for the supporting modifications, professional tuning, and the patience to do the installation right.

When everything comes together, the result is an Evo VIII that pulls with authority from corner to corner, delivers an exhilarating driving experience, and stands as a testament to the engineering potential of Mitsubishi's legendary 4G63 platform. Whether on the street, the autocross course, or the drag strip, the HKS GTII equips the Evo VIII with the power it always deserved.

For further reading on Evo VIII turbo upgrades and tuning, consult resources from HKS's official website for product specifications, and EvolutionM.net for community build threads and real-world dyno results from GTII-equipped vehicles.