Understanding the HKS GT-R Turbo Upgrade

HKS has been a dominant force in Japanese performance tuning for decades, and their turbo upgrade packages for the Nissan GT-R (R35) are among the most trusted in the industry. The stock VR38DETT engine is already a powerhouse, but its twin-turbo system uses relatively small IHI turbos that max out around 500-530 wheel horsepower on pump fuel. The HKS upgrade replaces these factory units with larger, high-flow turbos designed to move significantly more air while maintaining quick spool characteristics. The key engineering philosophy behind HKS’s approach is to offer a direct bolt-on solution that requires minimal fabrication, making the upgrade accessible to a wide range of owners — from street-driven cars to dedicated track machines.

The heart of the upgrade lies in the turbocharger specifications. HKS offers several tiers, ranging from the GTII series (good for 600-650 wheel horsepower) to the GTIII series (capable of 700+ wheel horsepower) and even the GTIV series for those chasing 800+ wheel horsepower with race fuel or E85. Each tier uses a twin-scroll design that separates exhaust pulses to reduce interference and improve spool time. The compressor wheels are machined from high-strength aluminum, while the turbine wheels use Inconel to withstand extreme exhaust gas temperatures. Unlike some budget kits that simply modify factory units, HKS turbos are completely new assemblies with upgraded bearing systems — typically journal bearings for the entry-level kits and ball bearings for the higher-end GTIII and GTIV setups, which provide lower friction and faster transient response.

Key Specifications Across HKS Turbo Models

To help you understand the range of options, here are the core specifications for the most popular HKS GT-R turbo upgrades. All figures represent the turbo cartridge dimensions (compressor inducer / turbine exducer) as measured by the manufacturer.

  • HKS GTII-770 (Entry-Level): Compressor 68mm, Turbine 62mm, Max boost ~1.7 bar, Max power ~620 whp (with fuel system upgrade)
  • HKS GTIII-900 (Mid-Range): Compressor 74mm, Turbine 66mm, Max boost ~2.2 bar, Max power ~750 whp (requires upgraded fuel system and intercooler)
  • HKS GTIII-1000 (High-End): Compressor 80mm, Turbine 72mm, Max boost ~2.5 bar, Max power ~850 whp (requires full supporting mods including built engine)
  • HKS GTIV-1000R (Race Grade): Compressor 78mm, Turbine 76mm, Max boost ~2.8 bar, Max power ~1000 whp (requires stand-alone ECU and built transmission)

It is vital to note that these power figures are measured at the wheels on a dynojet or similar chassis dyno with proper tuning. Crank horsepower (the number most often quoted in marketing) will be approximately 15-20% higher due to drivetrain losses. HKS publishes conservative, safety-oriented numbers to ensure reliability when the kit is installed with the minimum recommended supporting modifications.

Real Power Gains: From Stock to HKS-Equipped

The stock Nissan GT-R (2013-2021 model years) produces approximately 545-565 crank horsepower depending on the year and market. At the wheels, a stock GT-R typically dynos between 450 and 480 whp. With the HKS GTII-770 upgrade and the required fuel system (injectors and fuel pump), the same car will produce 620-640 whp on 93-octane pump gas. This represents a gain of roughly 170 wheel horsepower — a 35% increase.

Moving up to the GTIII-900 on pump fuel and a modest boost increase (1.8 bar), owners report 720-750 whp. With ethanol blends (E70-E85), the same hardware can push beyond 800 whp because ethanol’s higher latent heat of vaporization allows for more aggressive timing and boost. For example, a well-documented build from Driven Performance shows a GTIII-900-equipped R35 making 782 whp and 681 lb-ft of torque on E85 with the stock long block (still under 100,000 miles). This is a testament to the VR38’s robust design, but only if the tune is conservative and the fuel system is up to the task.

The maximum gains come when pairing the GTIII-1000 or GTIV-1000R with a built engine (forged pistons, rods, upgraded valve springs) and a massive fuel system. On dedicated race fuel (C16 or similar) at 2.5 bar, the GTIV-1000R has been recorded at 1020 whp at the hubs. However, such builds are extreme and require significant drivetrain upgrades, including the transmission (GR6 might need upgraded gear sets or a sequential conversion) and a triple-disc clutch.

Performance Metrics Beyond Horsepower

While dyno numbers impress on paper, real-world acceleration and lap times reveal the true capability of the HKS upgrade. Let’s examine key performance changes.

Acceleration (0-60 mph and Quarter Mile)

A stock 2017 GT-R with launch control will hit 60 mph in about 2.9 seconds and run the quarter mile in the low 11-second range at 123 mph. With the HKS GTII-770 kit and a supporting tune, the same car drops to a consistent 2.5-second 0-60 and a quarter mile in the high 10s at 130 mph. This improvement is largely driven by the increased area under the torque curve — the GTII-770 delivers over 500 lb-ft of torque by 3500 rpm, compared to the stock peak of 450 lb-ft around 4000 rpm.

For the GTIII-900 kit, quarter-mile times fall into the mid-10-second range with trap speeds exceeding 140 mph. Some owners with race fuel and optimized suspension have broken into the 9.9-second region, as documented on GTR Heritage builds. These figures, however, require a dedicated drag radial tire and a well-prepared surface to prevent wheelspin.

Track Performance (Lap Times)

On road courses, the HKS turbo upgrade transforms the GT-R’s behavior. The stock GT-R is criticized for heavy turbo lag in stock form, especially at low RPM. The HKS twin-scroll design, particularly with the ball-bearing options, reduces spool time by nearly 500 rpm. One tuner reported that a GTIII-900 car on pump gas shaved 2.5 seconds off the Nürburgring lap time compared to a stock GT-R (7:38 vs 7:40.5, with driver improvements factored). At Tsukuba Circuit, the same car was 1 second faster per lap despite carrying the same tires and brakes.

The extra grunt out of corners allows the driver to use a higher gear and reduce downshift frequency, which pays dividends on technical tracks.

Torque Delivery and Driveability

Stock GT-R torque peaks around 450-470 lb-ft and then drops off above 5500 rpm. HKS-equipped cars show a flatter torque curve, often exceeding 550 lb-ft from 3500 to 6500 rpm. This makes the car more responsive in daily driving — you don’t need to rev the engine to high RPM to pass on the highway. The trade-off is that the larger turbos increase lag slightly compared to the tiny stock units, but with proper tuning (and especially with the wastegate actuator options), the power delivery feels linear and predictable.

Required Supporting Modifications

No turbo upgrade operates effectively in isolation. The HKS kit includes the turbos, gaskets, and sometimes upgraded actuator springs, but you must address the following areas to avoid engine damage or poor performance.

Fuel System

The stock fuel injectors (rated at around 480 cc/min) and the single pump unit cannot support more than roughly 620 whp. For the GTII-770, HKS recommends upgrading to 1,000 cc/min injectors and a dual Walbro 450 pump setup (or a single brushless pump like the Aeromotive Phantom). For GTIII and above, you will need 2,000 cc/min injectors and a triple pump system, along with a fuel return line and boost-referenced fuel pressure regulator.

Intake and Exhaust

HKS markets a complementary intake kit (carbon intake tubes and high-flow filters) that reduces restriction. The stock intakes are known to become heat-soaked quickly. For exhaust, a full 3-inch downpipe and mid-pipe system is mandatory. The stock catalytic converters will melt under the increased flow and heat. Most owners pair the HKS turbos with the HKS Legamax or Silent Hi-Power exhaust for a balanced sound and minimal restriction.

Intercooler and Cooling

The stock intercooler is side-mounted and becomes heat-soaked after a few hard pulls. For the GTII-770, a larger stepped core intercooler (like the AMS or HKS Racing intercooler) is highly recommended. For GTIII and above, a full front-mount intercooler setup becomes necessary to keep intake air temperatures below 50°C. Additionally, upgrading the engine oil cooler and transmission cooler is wise to prevent overheating during extended track sessions.

Engine Management

HKS provides a boost controller and piggyback ECU options, but most professional tuners prefer a full stand-alone ECU like the Motec M142 or Syvecs. Alternatively, Cobb AccessPort with custom tuning is popular for street GT-Rs. The tune must account for the larger turbos’ greater air mass flow and the changed spool characteristics. Without proper calibration, the engine will run excessively lean, leading to detonation and potential piston failure.

Drivetrain Upgrades

The GR6 dual-clutch transmission can handle up to about 700 lb-ft of torque before clutches start slipping. For GTIII and above, an upgraded clutch pack (Dodson, SSP, or HKS) is essential. Many owners also install a billet bell housing and upgrade the transfer case drive chain. If you push beyond 750 whp on sticky tires, the front differential may also need reinforcement.

Real-World User Experiences and Common Feedback

Reading through GT-R forums like GT-R Life and NAGTROC reveals a pattern. Owners who install the HKS GTII-770 are uniformly pleased with the “OEM+” feel — the car retains its daily-driver civility but gains a noticeable shove in the mid-range. One owner reported that his 2013 GT-R with the GTII kit and full HKS exhaust felt “like a different car above 4000 rpm — it just keeps pulling to redline without the stock drop-off.”

For GTIII users, the feedback is more mixed. While the power is intoxicating, many note that the car becomes less forgiving in traction-limited conditions. A member on GTRLife.com commented: “With the GTIII-900 and 295mm tires, you need to be very careful with the throttle in second gear — even on dry pavement, it will break the rears loose at 60 mph.” However, those same users emphasize that with proper suspension settings (e.g., upgraded anti-roll bars and coilovers), the car remains remarkably stable at high speeds.

Maintenance is a recurring theme. Many users report that after 15,000-20,000 miles on a GTII kit, they needed to replace the turbo oil return lines due to heat-related cracking. HKS has since released updated silicone-lined lines to address this. Additionally, the larger turbos generate more underhood heat, so the stock engine bay heat shields may be insufficient — some owners wrap the downpipes and turbo housings with DEI titanium wrap.

Cost Considerations and Return on Investment

The HKS GTII-770 kit retails for approximately $5,500-$6,000 (turbos only). Add the required supporting modifications (fuel system $2,500, intake/exhaust $2,000, intercooler $1,500, tuning $1,200, and labor $2,500-3,000 for installation), and the total outlay is roughly $15,000 to $18,000. For the GTIII-900, the turbo kit alone costs about $8,000, and with all supporting mods including transmission upgrades, the total can exceed $35,000.

Is it worth it? For an owner who plans to keep the car for many years and enjoys a custom, high-horsepower experience, the HKS kit offers arguably the best balance of reliability and performance compared to other options like single turbo conversions (which can cost $20,000+ for the kit alone and require significant fabrication). The HKS upgrade is a proven, well-engineered solution that doesn’t compromise the car’s daily usability as much as more extreme setups.

Comparison with Competing Upgrades

Other popular GT-R turbo upgrades include products from AMS Performance (Alpha series), Sheptrans, and AAM Competition. The AMS Alpha 9 (up to 900 whp) is a direct competitor to the HKS GTIII-900. While AMS kits often include more comprehensive supporting components in the package price, HKS kits are generally regarded as having better spool characteristics and a more linear power curve. The AMS Alpha 12 (1200 whp) targets a higher niche. For the street-oriented buyer, the HKS GTII-770 offers a more affordable entry point with excellent drivability.

The AAM “Stage 4” turbos (76mm) are similarly priced and offer comparable power, but user reports suggest they require more frequent wastegate maintenance. Ultimately, the choice often comes down to local tuner familiarity — if your go-to tuner prefers HKS, stick with HKS to avoid troubleshooting issues.

Conclusion

The HKS GT-R turbo upgrade delivers genuine, measurable power gains that transform the vehicle from a competent supercar contender into a flex-fuel monster capable of embarrassing machines costing three times as much. Whether you opt for the entry-level GTII-770 or the extreme GTIV-1000R, the upgrade is well-documented, backed by decades of motorsport experience, and offers excellent value when compared to engine swaps or single turbo conversions. However, it is not a “plug and play” modification — it demands careful planning and investment in supporting systems to realize its full potential safely. For the dedicated enthusiast willing to commit to the supporting mods, the HKS kit remains one of the most rewarding upgrades available for the R35 GT-R, providing a significant increase in acceleration, lap times, and overall driving excitement without sacrificing the car’s dual-purpose nature.