The HKS GTII 3071R Turbo Kit has earned a strong reputation among performance enthusiasts as a reliable, bolt-on path to serious horsepower. Designed to deliver approximately 340 wheel horsepower (whp) on common four- and six-cylinder platforms, this kit combines HKS’s decades of turbocharging expertise with the proven 3071R compressor wheel. Whether you are building a street car, a weekend track weapon, or a daily driver with serious punch, the GTII 3071R offers a balanced upgrade that emphasizes drivability alongside peak output. This review dives deep into the kit’s features, installation realities, tuning requirements, and real-world performance to help you decide if it is the right choice for your build.

Overview of the HKS GTII 3071R Turbo Kit

The HKS GTII series originated as a direct successor to the earlier GT-series turbos, introducing advancements in bearing technology and compressor aerodynamics. The 3071R variant uses a 71mm compressor inducer and a 56mm turbine wheel, placing it in the sweet spot between quick spool and high flow. The kit is sold as a complete bolt-on assembly for several popular engine platforms, including the Nissan SR20DET, Toyota 2JZ-GTE, Nissan RB25/RB26, Subaru EJ20/EJ25, and Honda K-series, among others. HKS tailors the specific manifold, downpipe, and wastegate for each application, ensuring a near-direct fit with minimal fabrication.

The “GTII” designation indicates HKS’s second-generation turbine housing design, which features a divided inlet and optimized volute shape for improved exhaust gas flow. This design helps reduce backpressure and spool time while maintaining high peak efficiency. The 3071R is often compared to the larger 3076R and the newer XR-series turbos, but it stands out for its ability to produce 340–400 hp on pump gas with excellent transient response.

Key Features and Specifications

Bearing Technology

The HKS GTII 3071R uses a dual-ball-bearing cartridge rather than a traditional journal bearing. Ball bearings reduce rotor inertia and require less oil flow, resulting in faster spool and lower oil temperature. HKS’s bearing system is known for durability even under sustained high boost, thanks to heat-treated races and precision steel balls. This is a critical advantage for daily-driven vehicles where frequent stop-and-go can wear journal bearings prematurely.

Compressor Wheel and Housing

The compressor features a forged aluminum billet 71mm inducer wheel with an extended-tip design. This improves flow capacity and surge margin compared to earlier cast wheels. The compressor housing is available in multiple A/R ratios (commonly 0.50 A/R for quick spool or 0.60 A/R for top-end flow), but the GTII kit typically ships with a housing optimized for the target platform’s exhaust volume. The compressor map shows peak efficiency around 65–70% flow capacity, making it a great match for engines displacing 1.8 to 3.0 liters.

Turbine Housing and Wastegate

The turbine housing is made from high-nickel cast iron and features a divided T25/T28 or T3 flange depending on the kit version. A 38mm or 44mm external wastegate is included (or recommended) depending on the application, with a spring pressure of 10–14 psi. HKS’s own wastegate is known for smooth boost control and can be combined with an electronic boost controller for precise boost management. The internal wastegate option is limited on the GTII line to maintain flow, so most kits use an external gate with a dump tube or recirculation path.

What’s Included in the Kit

  • HKS GTII 3071R turbocharger assembly (with actuator)
  • Cast manifold specific to the engine (e.g., SR20, 2JZ, RB)
  • Downpipe with three- or four-bolt flange
  • Oil feed and drain lines (stainless steel braided)
  • Water coolant lines (if applicable)
  • Turbine-to-compressor coupler and gaskets
  • Exhaust hardware (studs, nuts, locking washers)
  • Installation manual (HKS part number reference)

Note that intercooler piping, a larger fuel system, and ECU tuning are not included and are considered mandatory upgrades to safely harness the extra airflow.

Installation Process: Step-by-Step and Pro Tips

Installing the HKS GTII 3071R kit is a straightforward job for someone with moderate mechanical experience—typically a weekend project if you have the right tools and a lift or jack stands. The following steps outline the general process for a front-engine, turbocharged vehicle (using a SR20DET as an example).

Step 1: Preparation and Safety

Disconnect the battery, drain the engine oil and coolant, and remove any components blocking access to the turbo area. You will need a torque wrench, socket set (metric and imperial), a pry bar, thread locker, and a tap and die kit for cleaning bolt holes. Always use new gaskets and copper nuts where specified.

Step 2: Remove Existing Turbo System

If the vehicle has an original or aftermarket turbo, disconnect the oil and coolant lines, unbolt the downpipe, and remove the manifold and turbo as an assembly. Inspect the studs on the exhaust manifold flange; replace any that are damaged. Clean the cylinder head threads thoroughly.

Step 3: Install the HKS Manifold

The HKS manifold is typically a cast tubular design. Apply a thin layer of anti-seize to the studs and torque the manifold to the cylinder head in a crisscross pattern (factory specifications: generally 35–45 ft-lbs for M10 studs). Do not overtighten—cast iron can crack if stressed unevenly.

Step 4: Mount the Turbocharger

Install the turbo onto the manifold using the supplied gasket and nuts. HKS recommends copper nuts because they resist galling. Torque to 30–35 ft-lbs in stages. Connect the oil feed line to the top of the turbo and the drain line to the bottom. Use the included banjo bolts with new crush washers. For the coolant lines, route them as per the manual—most HKS kits use a feed from a pressurized coolant port on the engine block and a return to the radiator or water pipe.

Step 5: Wastegate and Downpipe

Mount the external wastegate using a gasket between the manifold and the gate (if a separate gate is used). Connect the boost reference line from the compressor outlet to the wastegate’s top port. Install the downpipe, ensuring clearance to the chassis/subframe. It is common to need slight clearancing with a hammer or a spacer on some platforms. Use a three-bolt flange with a high-quality gasket or a V-band for easier removal.

Step 6: Air Intake and Intercooler Piping

You will need to fabricate or purchase a custom intake pipe from the turbo’s compressor outlet to the intercooler core. HKS offers optional silicone couplers and aluminum piping for common setups. Ensure the compressor surge valve (BOV) is properly routed to avoid compressor surge, especially at part throttle.

Step 7: Fuel and Tuning Preparations

Before starting the engine, upgrade the fuel pump (recommend Walbro 255lph or higher) and install larger injectors (550–800cc depending on target boost). The kit does not include these. You must have a programmable ECU or a piggyback tuner (e.g., Nistune, Haltech, AEM, Motec) to calibrate the air/fuel ratio and ignition timing. Running without tuning will cause engine damage quickly.

Step 8: Final Checks

Double-check all oil, coolant, and boost hose connections for leaks. Install a boost gauge and a wideband oxygen sensor for monitoring. Prime the oil system by disconnecting the fuel pump relay and cranking the engine for 10 seconds. Reconnect and start the engine, checking for oil pressure and coolant flow. Listen for unusual noises; an initial smoke cloud is normal as assembly lube burns off.

Performance Evaluation: Dyno Results and Driving Impressions

On the dyno, a properly tuned HKS GTII 3071R kit on a 2.0L SR20DET with 10:1 compression and 1.2 bar (17.4 psi) of boost typically produces 340–370 whp and 320–350 lb-ft of torque. On a 2.5L or larger engine (like 2JZ-GE or RB25), the same kit can reach 400+ whp at similar boost levels with a larger exhaust turbine housing. The power curve shows full torque by 3,800–4,200 rpm on a 2.0L, with a smooth taper to redline. This spool characteristic is significantly quicker than a GT3076R, which may not reach full boost until 4,500 rpm on the same engine.

“The HKS GTII 3071R transformed my SR-powered S13. It pulls hard from 3,500 to 7,500 rpm with zero lag. I daily drive it at 340 whp and it feels stock below 3,000 rpm—perfect for street use.” — Forum member on Zilvia.net

Real-World Driving Experience

Drivers consistently report improved throttle response and a broader powerband compared to larger turbos. The kit maintains good drivability in traffic because it retains enough low-end torque to pull from 2,500 rpm without clutch slipping. On the highway, passing acceleration is immediate. The turbo’s spool sound is a distinctive whistle that builds into a deep whoosh; the external wastegate adds a mechanical chatter under boost. Owners also note that the kit runs cooler oil temperatures than journal-bearing turbos, thanks to the ball-bearing’s lower frictional heat.

Track Performance

On road courses or autocross, the 3071R’s quick spool means you can stay in a higher gear through corners and still have power on exit. The power is linear and predictable, which aids traction. For drag racing, it can run low 12-second quarter-miles in a lightweight chassis (e.g., 2,600 lb S-chassis). With a boost controller, you can dial up to 1.5 bar for around 400 whp on race fuel, but engine internals (rods, pistons) become the limiting factor above 380 whp on stock bottom ends.

Tuning and Fuel System Requirements

To safely achieve 340 whp with the HKS GTII 3071R, you must address three critical areas: fuel delivery, engine management, and ignition.

Fuel System Upgrades

  • Fuel pump: Walbro 255lph or Deatschwerks DW300 is sufficient up to 400 whp.
  • Injectors: 550cc/min for 300–350 whp; 750cc/min for 400 whp (requires larger injectors and ECU recalibration).
  • Fuel pressure regulator: Required if using an aftermarket rail or larger injectors; set to 43 psi base.
  • Fuel lines: Stock lines are often adequate if they are in good condition, but braided PTFE lines are recommended for ethanol blends.

ECU Tuning Options

A chip tune or piggyback is no longer recommended for this power level—a standalone ECU is the best investment for reliability and performance. Popular choices include:

  • Haltech Platinum/Elite – plug-and-play for most Japanese engines.
  • AEM Infinity/EMS-4 – robust features and wide sensor support.
  • Nistune – cost-effective for Nissan OEM ECUs (requires daughterboard).
  • Link G4+ – excellent for Subaru and Toyota applications.

Boost control can be implemented via the ECU’s solenoid or a separate EBC (e.g., HKS EVC or AEM Tru-Boost). Set the base boost using the wastegate spring (typically 10 psi) and let the controller raise it to target.

Pros and Cons

Advantages

  • Bolt-on simplicity: No custom fabrication needed for most popular platforms.
  • Fast spool: Ball-bearing and efficient turbine housing minimize lag.
  • Proven reliability: HKS has supported this line for over a decade with available rebuild parts.
  • Excellent street manners: Maintains low-end torque and drivability.
  • Scalable: Capable of 400+ whp with proper fuel and tuning.

Disadvantages

  • Cost: The complete kit can exceed $3,000–$4,000, which is more expensive than some generic T3/T4 hybrids.
  • Requires supporting mods: Intercooler, fuel system, and ECU add significant expense.
  • Limited top-end: On large-displacement engines, a GT3076R or GTX3071R would offer more peak power potential.
  • Wastegate placement: On some chassis, the external wastegate can be tight against the firewall or frame rail, requiring a dump tube or relocation.
  • Availability: Some specific platform variants (e.g., Honda K-series) may be discontinued or hard to source.

Comparison with Other Turbo Kits

HKS GTII 3071R vs. Garrett GT3076R

The Garrett GT3076R is larger (76mm compressor) and supports up to 500 whp but spools later—typically 500–700 rpm later on a 2.0L engine. The 3071R is better for a quick-responding street car; the 3076R suits a higher-horsepower race application with a rev-happy engine.

HKS GTII 3071R vs. BorgWarner EFR 6758

The EFR 6758 uses an even smaller turbine wheel and integrated blow-off valve, offering similar spool to the 3071R but with a broader efficiency range. The EFR costs about the same but requires a more complex exhaust manifold due to its proprietary flange. The HKS kit wins on simplicity and platform-specific fitment.

HKS GTII 3071R vs. Precision 5858

Precision’s 5858 is journal-bearing and cheaper, but it lacks the ball-bearing spool speed and durability. The 5858 can achieve similar power numbers, but enthusiasts often prefer the HKS for its immediate response and higher quality materials.

Buying Guide and Final Thoughts

When purchasing an HKS GTII 3071R Turbo Kit, verify that the part number matches your engine and chassis. HKS uses different sub-part numbers for SR20 (kit 1401-RM001), 2JZ (1401-RM002), RB25 (1401-RM003), and others. Buy from an authorized HKS dealer to avoid counterfeit components. Expect to pay between $2,500 and $3,800 for the complete kit (turbo, manifold, downpipe, lines, wastegate).

Before buying, also budget for the necessary upgrades: front-mount intercooler ($300–$800), fuel system ($300–$600), and ECU and tuning ($600–$1,500). The total investment to run safely at 340 hp will be in the range of $4,500–$6,500, not including labor. For most owners, this represents a solid value when compared to rebuilding a larger engine or converting a turbo from another platform.

In conclusion, the HKS GTII 3071R Turbo Kit delivers on its promise of a high-quality, bolt-on 340+ hp upgrade. Its combination of fast spool, robust construction, and direct fit makes it a top choice for enthusiasts who want a turnkey increase in power without the headaches of custom fabrication. Whether you are building a street machine or a track-day toy, this kit offers a proven, reliable path to impressive performance. For more detailed specs and to verify compatibility, visit the official HKS product catalog at HKS Global or consult with a trusted tuner like Sound Performance for tuning support. Additional community feedback can be found on forums like SR20 Forum.