Understanding the HKS GT II Turbo for RB20DET

The RB20DET, Nissan’s 2.0‑liter turbocharged inline‑six, has long been a favorite among JDM enthusiasts and drift builders. While the stock turbocharger delivers adequate response for a 1980s design, serious power gains demand a modern upgrade. The HKS GT II Turbo is a bolt‑on replacement that bridges the gap between quick spool and high‑rpm horsepower, making it one of the most popular choices for road‑going RB20DET builds.

Turbo Specifications and Design

The HKS GT II Turbo is a twin‑scroll turbocharger built around a 50‑trim compressor wheel and a 60‑trim turbine wheel, housed in a lightweight, high‑flow cast turbine housing. Key design features include:

  • Journal bearing center section – proven durability for street use with lower cost than ball‑bearing units
  • High‑nickel cast turbine housing – reduces thermal cracking and improves heat retention
  • Optimized A/R ratio – typically 0.60 A/R for the turbine side, balancing low‑end response with top‑end flow
  • Integrated wastegate port – allows direct bolt‑on to factory exhaust manifolds with minor modifications

These specs make the GT II an ideal candidate for RB20DET owners who want a noticeable power bump without sacrificing daily drivability.

Ideal Applications

This turbo excels in setups aiming for 280–350 wheel horsepower on pump fuel. Common uses include street‑driven track cars, time‑attack builds, and drift machines where throttle response and mid‑range torque are critical. The twin‑scroll design helps the small 2.0‑liter engine spool the turbo quickly, often reaching full boost by 3,500 rpm.

Cost Breakdown: What You Need to Budget

Installing the HKS GT II Turbo is more than just buying the turbo itself. Proper planning and budgeting for supporting modifications, labor, and tuning will ensure a reliable, high‑performance result.

Turbocharger Pricing

The HKS GT II Turbo new typically retails between $1,500 and $2,500 USD, depending on the specific variant (e.g., GT II, GT II‑S) and the supplier. Used units in good condition can be found for $1,000–$1,500, but inspection of shaft play and seal condition is essential. Authorized HKS dealers and reputable JDM parts importers are the safest sources.

Installation Labor Costs

Professional installation of a turbo upgrade on an RB20DET generally runs $500 to $1,000. This includes removal of the stock turbo, bolting on the HKS unit, and basic fabrication if bracket modifications are required. If you are comfortable with a wrench and have a weekend available, you can perform the install yourself and save this cost, but be prepared for a tight workspace under the plenum.

Supporting Modifications

The HKS GT II flows significantly more air than the stock turbo. To realize its potential safely, you will need:

  • Front‑mount intercooler (FMIC) kit – $300–$600
  • Free‑flowing exhaust – downpipe, midpipe, and cat‑back system: $400–$800
  • High‑flow intake – pod filter with cold‑air box: $100–$200
  • Fuel system upgrades – 550 cc injectors (or larger) and a Walbro 255 lph fuel pump: $300–$500
  • Boost controller – manual or electronic: $50–$300
  • Engine management and tuning – see below

Total for supporting mods: roughly $1,150 to $2,400.

Tuning and Dyno Time

Even the best hardware will fail without proper calibration. Expect to pay $500 to $1,000 for a professional dyno tune using a standalone ECU (like the Haltech Elite 1500 or Link G4+) or a piggyback (e.g., Nistune, Power FC). This cost includes map development, boost calibration, and final power runs.

Estimated Total Budget

Considering all factors, a complete HKS GT II upgrade on an RB20DET should be budgeted as follows:

  • Turbocharger: $1,500–$2,500
  • Labor (if not DIY): $500–$1,000
  • Supporting modifications: $1,150–$2,400
  • Tuning: $500–$1,000
  • Miscellaneous (gaskets, lines, oil): $200–$400

Total estimated range: $3,850–$7,300. While that may seem steep, the resulting power and reliability make it a worthwhile investment for serious enthusiasts.

Performance Gains: What to Expect

When paired with the supporting modifications listed above, the HKS GT II Turbo transforms the RB20DET from a mild 200‑hp factory tune into a responsive, powerful setup.

Horsepower and Torque Increases

On a healthy engine with proper tuning, the HKS GT II typically delivers 280–350 wheel horsepower (whp) and 290–340 lb‑ft of torque. Compared to the stock RB20DET’s 210‑ish crank horsepower (≈170 whp), you are looking at a 60–100% increase in wheel horsepower. The torque curve also rises dramatically, with peak torque arriving earlier in the rev range.

Spool Characteristics and Driveability

One of the GT II’s strongest attributes is its spool behavior. Full boost (around 14–16 psi) arrives by 3,500–3,800 rpm, depending on exhaust configuration. This means you get strong mid‑range pull without the lag of a bigger turbo. For street driving and drifting, this response is invaluable—you can stay in the powerband without constantly shifting gears.

Real‑World Dyno Examples

While results vary by condition, a typical RB20DET with the HKS GT II, 3‑inch exhaust, front‑mount intercooler, and 550 cc injectors tuned on 93 octane sees 290–310 whp and 300–310 lb‑ft at around 14 psi. With boost increased to 18–20 psi and water‑methanol injection, some builds push past 350 whp. These numbers are consistent with data shared on enthusiast forums and HKS’s own literature.

Installation Process: Step‑by‑Step

Installing the HKS GT II Turbo on an RB20DET is a weekend project for experienced hobbyists. Below is a high‑level overview. Always consult the factory service manual and the HKS fitting instructions for torque specs.

Pre‑Installation Preparation

  1. Disconnect the battery and drain the coolant and engine oil.
  2. Remove the intake piping, air filter box, and intercooler piping.
  3. Unbolt the exhaust downpipe from the turbo and separate the exhaust manifold from the cylinder head.

Removing the Stock Turbo

Unscrew the oil feed line from the turbo center cartridge. Disconnect the water coolant lines at the banjo bolts. Remove the four nuts holding the turbo to the exhaust manifold, then carefully lift the turbo out from the engine bay (it may require manipulation due to the tight space).

Installing the HKS GT II

Apply new gaskets to the exhaust manifold and turbo flange. Orient the HKS turbo so the compressor housing matches your intercooler piping direction. Bolt the turbo to the manifold using the provided hardware, torquing to 35–40 lb‑ft. Connect the oil feed (use a restrictor if recommended for journal bearing turbos) and the water return lines.

Upgrading Intake, Exhaust, and Intercooler

While the turbo is out, it’s an ideal time to fit the front‑mount intercooler kit, larger injectors, and the new 3‑inch downpipe. Ensure all couplers are tight and the wastegate actuator can move freely. Route the new intake pipe through the fender or directly to a cone filter.

Final Assembly and Checks

  1. Reinstall the exhaust manifold heat shield (if retaining) and the intake plenum.
  2. Refill engine oil and coolant. Prime the turbo by disabling the fuel pump and cranking for 10 seconds.
  3. Start the engine and check for leaks. Let it idle to circulate oil through the turbo.
  4. Perform a boost leak test on all intake and intercooler connections.

Supporting Modifications: Essential Upgrades

Skimping on supporting mods is the fastest way to turn a performance gain into a blown engine. Here are the non‑negotiable upgrades.

Fuel System Upgrades

The stock RB20DET injectors (440 cc) max out around 260 whp. For the HKS GT II, upgrade to 550 cc or 740 cc injectors and a high‑flow fuel pump (Walbro 255 or AEM 320). Also consider a fuel pressure regulator to maintain stable pressure under boost.

Ignition and Engine Management

A stock RB20DET ignition system can handle moderate boost, but after 14 psi you may experience misfire. Upgrade coil packs (e.g., Splitfire or OEM replacements with fresh plugs). A standalone ECU or a well‑mapped piggyback like Nistune is essential to properly control fuel and timing. Many tuners recommend the Haltech or Link ECUs for their RB20 base maps.

Cooling and Lubrication

Higher boost generates more heat. Install an oil cooler kit (thermostatic sandwich plate with 19‑row core) and a larger radiator (Koyo or PWR aluminum) to keep temperatures in check. Use high‑quality synthetic oil (15W‑50 for street/track) and consider an aftermarket thermostat for lower operating temps.

Potential Challenges and Troubleshooting

Even with careful planning, you may encounter issues during or after installation. Here are common problems and how to address them.

Fitment and Clearance Issues

The HKS GT II is designed as a direct bolt‑on, but clearance to the engine block or alternator can be tight. In some cases, you may need to adjust the oil drain line angle or use a narrow fan clutch for clearance. Test fit the turbo before final bolt‑up.

Boost Control and Wastegate Setup

The GT II’s internal wastegate is adequate for 14–16 psi. For higher boost, you’ll need an electronic boost controller and possibly a stiffer wastegate spring. Over‑boosting can lead to detonation. Always set a low‑boost base map before fine‑tuning.

Oil and Water Line Routing

The HKS turbo may require different banjo bolts or hose adapters. Verify the orientation of the oil feed restrictor (if used). A common mistake is installing a restrictor of too small orifice, starving the turbo of oil. HKS recommends a 1.5 mm restrictor for journal bearing versions.

ECU Tuning Pitfalls

Many aftermarket ECUs have base maps designed for other engines. You must log idle, cruise, and wide‑open throttle fuel trims. Watch for knock at the torque peak. If you are using a MAF sensor, upgrade to a larger one (e.g., Z32 MAF) with proper scaling in the ECU. Without careful tuning, you risk leaning out the mixture under boost.

Comparing the HKS GT II to Other RB20DET Turbo Options

While the GT II is a strong performer, it’s not the only game in town. Here’s how it stacks up against two other popular choices.

vs. Garrett GT2860RS (Disco Potato)

The GT2860RS (often called the Disco Potato) offers similar power but with a ball‑bearing center section that provides faster spool and better transient response. However, it costs $500–$800 more new. For drag racing or high‑boost applications, the Disco Potato may pull ahead; for street and drift, the GT II’s journal bearing is more cost‑effective and reliable.

vs. BorgWarner S200SX

The BorgWarner S200SX (e.g., 52‑trim) is a popular budget choice for RB20 builds. It can produce up to 400 whp but with noticeable lag. The GT II’s twin‑scroll design gives it superior low‑end response, making it the better choice for daily driving and technical tracks.

Which One Is Right for You?

Choose the HKS GT II if you prioritize mid‑range torque, have a budget of around $5,000 total, and want a proven bolt‑on solution with great street manners. If you plan to push past 350 whp or do frequent track days, a ball‑bearing unit like the Garrett GTX3071R may be worth the extra cost. For a comprehensive guide on turbo selection, check HKS official turbo details and SKYLINE SAU Forums for owner experiences.

Conclusion

Installing the HKS GT II Turbo on your RB20DET is a rewarding upgrade that delivers a substantial increase in horsepower and torque while maintaining excellent drivability. The total cost—including turbo, supporting mods, and tuning—ranges from roughly $4,000 to $7,300, but the result is a responsive, reliable engine capable of 280–350 wheel horsepower. Plan your build carefully, invest in quality components, and don’t skip the dyno session. With the right preparation, this upgrade will transform your RB20DET into a high‑performance machine that excels on street, drift, or track.