Upgrading the turbocharger system on a Nissan GT-R (R35) is one of the highest-impact modifications you can make to unlock the car's true performance potential. The VR38DETT engine is a robust and capable platform, but the stock twin-turbo setup limits top-end power delivery and airflow capacity. The Powermax 68mm turbocharger has emerged as a leading drop-in upgrade, offering a strong balance of spool response, flow capability, and direct bolt-on convenience without the fabrication required for a full top-mount or single-turbo conversion.

This guide covers the complete scope of the Powermax 68mm upgrade—from prerequisite supporting modifications and the installation process to tuning strategy and real-world performance results. Whether you are performing the work yourself or overseeing a shop build, understanding the technical details ensures a reliable and high-output outcome.

Understanding the GT-R Turbo Upgrade Path

The R35 GT-R left the factory with a pair of IHI turbochargers. While adequate for the stock 480-600 horsepower target (depending on model year), these turbos become a restriction once boost levels and airflow demands increase. Upgrading the turbochargers opens up the mid-range and top-end power band significantly.

There are three primary routes for GT-R turbo upgrades:

  • Drop-in / Hybrid turbos (e.g., Powermax 68mm, GCG, AMS). These use upgraded compressor and turbine wheels within the stock housing locations for a direct bolt-on fit.
  • Full-frame / Stage 3 turbos (e.g., AMS GT28, PTE 6266/6466). These replace the entire turbocharger assembly and require modification to the engine bay.
  • Single-turbo conversions (e.g., ETS, Sound Performance). These remove the twin-turbo setup entirely for a large single unit. While capable of massive power, they introduce spool lag and significant complexity.

The Powermax 68mm sits firmly in the "hybrid" category, making it an appealing option for owners targeting 650-750 whp without the installation complexity or spool penalty of a full-frame system.

Powermax 68mm Turbocharger Specifications

The Powermax 68mm is an upgraded hybrid turbocharger designed to replace the stock IHI units. Key specifications include:

  • Compressor Inducer: 68mm
  • Turbine Wheel: Upgraded billet wheel (typically 58-60mm)
  • Housing: Cast 5-bolt outlet, V-band inlet
  • Wastegate: Internal (external wastegate upgrade recommended for high boost)
  • Actuator: Heavy-duty adjustable actuator for consistent boost control

Compared to a stock VR38DETT turbo, the Powermax 68mm flows roughly 30-40% more air at the same boost pressure. This translates directly to power gains, particularly in the 4,500-7,200 RPM range. The improved billet compressor wheel is designed for higher rotational speeds and better efficiency, reducing intake air temperatures (IATs) under sustained load. For detailed technical specs and flow maps, consult reputable distributors like AMS Performance.

Required Supporting Modifications

Installing a Powermax 68mm turbo without addressing the supporting systems will lead to limited gains and potential engine damage. The engine management, fuel system, and intake/exhaust paths must all be upgraded to match the increased airflow.

Fuel System Upgrades

Higher horsepower requires more fuel volume. The factory fuel pumps and injectors are insufficient beyond 550 whp. For a Powermax 68mm build targeting 650-750 whp, you will need:

  • Fuel Injectors: 1,000cc - 1,300cc injectors (Injector Dynamics ID1300 or equivalent).
  • Low-Pressure Fuel Pump: A Walbro 525, AEM, or equivalent in-tank pump.
  • High-Pressure Fuel Pump (HPFP): Drop-in upgraded HPFP internals (e.g., Syvecs, T1) to maintain rail pressure under high load.
  • Flex Fuel Capability: Strongly recommended. Running E85 (or a high-ethanol blend) allows for more aggressive timing and lower IATs.

Intake and Induction

  • Intake System: A high-flow cold air intake or dual intake setup (e.g., AMS, ETS) to reduce restriction.
  • Turbo Inlets: Upgraded 2.5" or 3" inlets are mandatory. The stock rubber inlets collapse under the increased suction of the 68mm compressor.
  • Intercooler: An upgraded front-mount intercooler core (e.g., ETS 3" or AMS Alpha) is non-negotiable to keep IATs under control during sustained pulls.

Exhaust System

  • Downpipes: Cat-less downpipes (3" or 4") to reduce back-pressure and improve spool.
  • Mid-Pipes: Upgraded mid-pipes (often 3" stainless steel) to match downpipe flow.
  • Cat-Back Exhaust: A free-flowing cat-back reduces exhaust gas temperature (EGT) and helps spool the larger turbine wheel.

Installation Process

Installing the Powermax 68mm turbos on a GT-R is a moderately complex job best suited to experienced DIY mechanics or professional shops. The process typically takes 8-16 hours depending on skill level and any unforeseen complications.

Tools and Parts Required

  • Metric socket set (10mm, 12mm, 14mm, 17mm, 19mm)
  • Torque wrench (ft-lb and in-lb)
  • Turbocharger installation kit (gaskets, o-rings, copper washers)
  • New oil return line gaskets and coolant line seals
  • Anti-seize compound
  • Engine support bar or hoist (for lowering the engine cradle)

Removal of Stock Components

Start by disconnecting the battery negative terminal. Drain the engine oil and coolant. Remove the intake pipe, air boxes, and engine cover. To access the rear turbo (passenger side), remove the heat shields, rear downpipe, and oil/water lines. The front turbo (driver side) requires removal of the intercooler piping, front downpipe, and in some cases the front half-shaft. Loosening the engine mounts and lowering the engine cradle by 2-3 inches is standard practice to access the lower turbo bolts.

Powermax 68mm Installation

Before bolting on the new turbos, verify the wastegate actuator preload. Set it to the manufacturer's specifications (typically 8-12 psi of preload). Transfer necessary fittings from the stock turbos (oil feed restrictors, coolant fittings). Install the turbocharger to the exhaust manifold using new gaskets. Tighten to factory torque specs (typically 35-40 ft-lb for the manifold nuts). Reconnect the oil return lines with new gaskets and O-rings, then connect the coolant supply and return lines.

Reassembly and Final Checks

Reinstall the downpipes, intake piping, intercooler, and half-shaft. Refill with fresh engine oil and coolant. Connect the boost reference line to the wastegate actuator. Double-check all clamps, hoses, and electrical connections. Perform a pressure test on the intake system to check for leaks before starting the engine. Once confirmed, start the engine and check for oil pressure and coolant circulation. Let the engine idle and inspect for any fluid leaks.

Tuning and Calibration

The Powermax 68mm turbocharger alters the engine's airflow characteristics significantly. The stock ECU calibration cannot compensate for this increased airflow. Tuning is mandatory. Without proper calibration, the engine will run excessively lean, causing detonation and severe damage.

Choosing a Tuning Platform

The two primary tuning platforms for the R35 GT-R are ECUTEK and Cobb Accessport. ECUTEK is currently the industry standard for GT-R calibration, offering advanced flex-fuel logic, launch control, and flat-foot shifting. Cobb remains a viable option for earlier model years but lacks the deep integration ECUTEK provides for later DBW throttles and flex fuel systems.

Base Mapping and Dyno Tuning

If you install the turbos yourself, drive the car gently (tip-in throttle, no boost) to a professional tuner. Do not attempt to apply heavy throttle. During the dyno session, the tuner will dial in:

  • Fuel Trims: Adjusting injector latency and scalars to hit target air/fuel ratios (11.0-11.5:1 on pump gas, 11.8-12.2:1 on E85).
  • Ignition Timing: Optimizing timing for maximum torque without knock. Higher timing values are achievable on ethanol due to its higher octane rating.
  • Boost Control: Setting target boost. A Powermax 68mm on pump 93 typically peaks near 20-22 psi. On E85, 24-27 psi is common.
  • Transmission Calibration: Adjusting shift pressure and torque converter lockup to handle the increased power safely.

For detailed tuning guidance and platform information, refer to ECUTEK or professional tuning shops like Driven Performance.

Performance Results and Benchmarks

When properly supported and tuned, a Powermax 68mm turbocharger transforms the GT-R. The gains are substantial across the entire power band, with the most impressive improvements occurring in the mid-range and top-end.

Dyno Results

On a Mustang Dyno or Dynojet, a GT-R with a Powermax 68mm upgrade, supporting fuel system, and intercooler typically produces:

  • Pump 93 Octane (22 psi): 620-660 whp / 580-620 wtq
  • E85 Flex Fuel (26 psi): 700-760 whp / 650-700 wtq
  • E85 Race Fuel (28+ psi): 780-820 whp / 700+ wtq

Spool Characteristics

One of the main advantages of the 68mm hybrid design is its spool behavior. Full boost (20+ psi) is typically reached by 3,800-4,000 RPM. This is a modest delay of approximately 300-500 RPM compared to the stock turbos, but the trade-off is an extra 150-250 whp up top. The car pulls hard to the 7,200 RPM redline without significant power drop-off.

Drag Strip Performance

A well-tuned GT-R with a Powermax 68mm on E85, supported by sticky tires (e.g., 315/30/18 Hoosiers or Michelin Pilot Sport Cup 2s), can run 9.9-10.5 second quarter-mile times at 135-145 mph. This represents a massive performance gain over the stock 11.5-12.0 second timeslips.

Long-Term Maintenance and Reliability

Operating at 700+ whp requires disciplined maintenance. The turbocharger itself is robust, but the supporting systems need regular attention.

Oil Management

The Powermax 68mm is available with journal bearings or ball bearings depending on the specific version. Journal bearing turbos require a steady supply of clean oil. Change your oil every 3,000-3,500 miles using a high-quality synthetic 5W-40 or 10W-40 oil (e.g., Motul 300V, Mobil 1 Euro).

Monitoring and Gauges

Install a quality boost gauge, wideband air/fuel ratio gauge, and oil pressure gauge. If you data log, watch for knock correction. Frequent knock events indicate a tuning issue or bad fuel. Monitor oil temperature; sustained oil temps above 260°F warrant an oil cooler upgrade.

Common Issues and Inspection Points

  • Boost Leaks: The increased pressure can blow off weak couplers or inlet hoses. Inspect all connections after the first few heat cycles.
  • Wastegate Creep: Some Powermax 68mm setups may experience boost creep if the internal wastegate is not properly ported or if the actuator is weak. An external wastegate dump is a popular solution for high-horsepower builds.
  • Fuel Pump Failure: High-horsepower builds stress the in-tank fuel pump. Carry a spare or upgrade to a brushless pump for better reliability during track use.

Is the Powermax 68mm Right for Your Build?

The Powermax 68mm turbo upgrade is an excellent choice for the GT-R owner who wants genuine 700+ whp capability without the complexity, expense, or lag of a top-mount single turbo system. It is a direct bolt-on that respects the factory engineering constraints while dramatically boosting performance.

If you are targeting 600 whp or less, the stock turbos with a tune and supporting mods may suffice. If you are aiming for 900+ whp, full-frame or single turbo options are more appropriate. For the majority of street-driven GT-Rs—cars that see daily driving, canyon runs, and occasional track days—the Powermax 68mm delivers the optimal balance of response, power, and drivability.

Work with a reputable tuner, invest in the supporting modifications, and enjoy the transformation. For further reading on turbo selections and build strategies, consult forums like GT-R Life and NAGTROC for community dyno sheets and detailed build threads.