The Holset HX35 turbocharger upgrade is a proven path to substantial power gains for Genesis G70 owners seeking to push beyond factory limits. This comprehensive guide covers everything from turbo specifications and supporting modifications to detailed installation steps and real-world performance expectations. Whether you own the 2.0T Theta II or the 3.3T Lambda II engine, understanding the HX35 platform will help you make an informed decision and execute a successful upgrade.

What is the Holset HX35 Turbocharger?

The Holset HX35 is a medium-frame turbocharger originally designed for heavy-duty diesel applications like the Cummins 5.9L 12-valve. Its reputation for durability, surprisingly low cost, and excellent flow capacity has made it a go-to choice for gasoline engine swaps and upgrades. Key specifications include:

  • Compressor wheel: 56mm inducer / 76mm exducer (non-gated version) or 54mm / 76mm (gated version)
  • Turbine wheel: 65mm inducer / 75mm exducer (twin-scroll capable)
  • Compressor housing A/R: 0.70 (standard)
  • Turbine housing A/R: 0.84 or 0.92 (external wastegate models)
  • Maximum flow: Approximately 550–600 hp on gasoline engines

The HX35's robust journal bearing design and large turbine housing enable impressive top-end power while maintaining reasonable spool characteristics when paired with proper engine displacement and tuning. Modern versions from Holset's HE series borrow the same core dimensions with updated aerodynamics.

Why Upgrade Your Genesis G70's Turbo?

The G70's factory turbocharger is engineered for a balance of low-end torque, emissions compliance, and reliability across a wide range of driving conditions. However, pushing beyond stage 1 tuning levels (around 300–320 whp on the 2.0T) quickly reveals the stock turbo's limitations:

  • Compressor surge at high boost levels
  • Excessive exhaust back pressure
  • Heat soak under sustained load
  • Fixed geometry wastegate limits boost control

Upgrading to a Holset HX35 addresses these shortcomings by offering a much larger compressor and turbine, lower back pressure, and the ability to run higher boost safely. With proper supporting modifications, the HX35 can deliver 350–400 whp (2.0T) and potentially 450+ whp (3.3T with twin-scroll configuration) while maintaining reliable daily drivability.

Compatibility and Supporting Modifications

Engine Variants

The Genesis G70 is offered with two engine options: the 2.0L Theta II turbocharged inline‑4 and the 3.3L Lambda II twin‑turbo V6. The HX35 upgrade is most commonly applied to the 2.0T due to its simpler single‑turbo architecture. For the 3.3T, owners typically retain the twin‑turbo layout and upgrade to larger units such as Holset HE351 or BorgWarner EFR 7163. This guide focuses on the 2.0T application, though many principles translate to single‑turbo conversions on the V6.

Required Supporting Upgrades

Simply bolting on an HX35 without addressing fuel, intake, exhaust, and cooling systems will yield poor results and risk engine damage. Plan for these essential modifications:

  • Fuel system: Larger injectors (750–1000 cc), high‑flow fuel pump (e.g., Walbro 450 or DW300c), and upgraded fuel pressure regulator
  • Intercooler: Front‑mount intercooler with bar‑and‑plate core at least 3 inches thick to handle increased heat load
  • Intake: 3‑ or 3.5‑inch cold air intake with a high‑flow filter; the stock airbox is restrictive
  • Exhaust: Full 3‑inch downpipe (catless or high‑flow cat), 3‑inch mid‑pipe, and cat‑back exhaust to reduce turbine back pressure
  • Wastegate: External 44–50 mm wastegate to control boost precisely, typically vented to atmosphere or recirculated
  • Blow‑off valve: Vented BOV (e.g., Tial Q, GFB Mach 2) to prevent compressor surge during throttle closure
  • Oil and coolant lines: Custom braided lines with AN fittings; the HX35 uses a 1/8 NPT oil feed and 3/4–16 oil return
  • Clutch: Stage 2 or upgraded clutch to handle the additional torque (manual transmissions)

Tuning Considerations

After installation, a custom tune is non‑negotiable. The HX35's larger trim and flow characteristics require revised fuel, ignition, and boost tables. Options include:

  • Standalone ECU (e.g., Haltech Elite 1500, Motec M150) – full control, best for high‑power builds
  • Piggyback or flash tune (e.g., EcuTek, Cobb Accessport with custom calibration) – less invasive, sufficient for 350–400 whp
  • Professional dyno tuning is strongly recommended over mail‑order maps, as every engine behaves differently
Caution: Operating an HX35 without proper tuning can lead to dangerously lean mixtures, detonation, and engine failure. Always verify air‑fuel ratios and timing under load before driving the car aggressively.

Step‑by‑Step Installation Guide

Before starting, allow a full weekend for the job. You will need a socket set (10–19 mm), wrenches, torque wrench, 3‑inch hole saw (if enlarging the downpipe), and a set of new gaskets for the turbo manifold, downpipe, and exhaust flanges. Ensure you have the correct adapter plate if your G70's manifold does not directly accept the T3/T4 flange – the HX35 typically uses a T3 turbine housing.

Pre‑Installation Preparation

  • Disconnect the battery negative terminal
  • Drain engine coolant and engine oil (reuse only if fresh; otherwise replace)
  • Remove the engine under‑tray and front bumper cover for access
  • Inspect the HX35: spin the compressor wheel, check for axial and radial play (0.002–0.004 inch is acceptable), and verify the wastegate opens smoothly
  • Install the turbo gasket kit and thread lock compound on critical bolts

Removing the Stock Turbocharger

  1. Remove the heat shields covering the turbo and exhaust manifold
  2. Disconnect the oxygen sensors (front and rear, if equipped)
  3. Unbolt the downpipe from the turbine outlet and the catalytic converter
  4. Disconnect the oil feed line from the top of the turbo and the oil return line (usually a large banjo bolt)
  5. Remove the coolant lines from the turbo core
  6. Unplug the wastegate actuator vacuum line
  7. Unbolt the turbo from the exhaust manifold (typically four nuts on studs)
  8. Carefully lift the stock turbo out from the top or bottom, depending on clearance

Installing the Holset HX35

  1. If using a T4 adapter (not recommended on 2.0T for spool), install it with new gasket and torque to spec
  2. For a direct T3 fitment, place the new gasket on the manifold studs
  3. Position the HX35 on the manifold, ensuring the oil drain port faces downward (at an angle between 0–15 degrees from vertical)
  4. Secure the turbo with new lock washers and nuts; torque to 35–40 ft‑lbs in a cross pattern
  5. Clock the compressor housing as needed for intake piping clearance (loosen the V‑band clamp, rotate, and retighten to 45 in‑lbs)
  6. Install the external wastegate on the manifold or a dedicated dump tube; route vacuum line from the wastegate to the boost controller
  7. Connect the oil feed line (use a restrictor if the HX35 shows excessive crankcase pressure – typically 0.040–0.060 inch orifice)
  8. Connect the oil return line (10‑AN or 12‑AN line with a low‑profile fitting to avoid clearance issues)
  9. Install coolant lines; the HX35 does not require coolant circulation for street use, but it is recommended for longevity

Reconnecting Piping and Hoses

  • Fit the intake pipe with a 4‑inch coupler to the HX35 compressor inlet
  • Route the charge pipe from the compressor outlet to the intercooler (3‑inch aluminum pipe recommended)
  • Attach the intercooler outlet to the throttle body via 2.5‑inch pipe
  • Connect the downpipe to the turbine outlet; use a 3‑inch flexible section to absorb vibration
  • Reinstall the oxygen sensors in the appropriate bungs
  • Install blow‑off valve on the charge pipe before the throttle body
  • Connect boost reference line to the wastegate and boost controller

Final Checks and First Start

  • Double‑check all clamps, bolts, and fittings
  • Refill oil and coolant; prime the oil system by cranking the engine with the fuel pump fuse removed (10‑second intervals)
  • Reconnect the battery and start the engine; let it idle for 15 minutes, checking for leaks
  • Monitor oil pressure and coolant temperature on the scan tool
  • Conduct a gentle test drive – keep boost under 10 psi initially
  • After 100 miles, retorque the exhaust manifold nuts and check all fluid levels

Expected Power Gains and Performance

With the supporting modifications listed above, a 2.0T Genesis G70 equipped with a Holset HX35 can achieve the following typical results:

  • Wheel horsepower: 320–380 whp (pump 93 octane) – 40–100 whp gain over stock Stage 2 tune
  • Torque: 290–340 lb‑ft, with a peak around 3500–4500 rpm
  • Boost pressure: 18–24 psi, tapering slightly to avoid compressor surge
  • Spool characteristics: Full boost by 3400–3800 rpm (compared to 2800 rpm stock), lag more noticeable but acceptable

On a dyno, the HX35's power curve remains flat well past 6500 rpm, unlike the stock turbo which falls off after 5500 rpm. For higher octane (E85), output can rise to 420–460 whp with appropriate fuel system upgrades. The 3.3T using a single HX35 conversion (with custom manifold) can potentially exceed 500 whp, but complexity and cost rise significantly.

Real‑world driving: The HX35 excels on highway pulls and track days where sustained high‑rpm power is needed. Daily driving is manageable but requires caution in stop‑and‑go traffic due to increased spool threshold. Proper boost control and a responsive tune make the car unexpectedly easy to drive for its power level.

Potential Challenges and Troubleshooting

  • Oil leaks: The HX35's journal bearing system requires proper oil feed restriction. Install a restrictor (0.040 inch) if you see blue smoke at idle or oil dripping from the exhaust.
  • Boost creep: Large turbine housings without proper wastegate flow can cause overboost. Use a 44 mm+ wastegate and ensure the dump tube is not restricted.
  • Compressor surge: Occurs when the BOV is too small or positioned incorrectly. Symptoms include a fluttering sound during gear changes. Upgrade to a larger recirculation valve.
  • Fitment issues: The HX35 is physically larger than the stock turbo; you may need to trim the engine bay heat shield or relocate the coolant reservoir. Aftermarket motor mounts reduce engine movement.
  • Tuning complexity: Expect multiple revisions if tuning via mail‑order. A professional dyno session with a familiar calibrator is worth the investment.

Conclusion

The Holset HX35 turbo upgrade transforms the Genesis G70 2.0T into a serious performance machine capable of competing with cars costing twice as much. While the installation requires moderate mechanical skill and a willingness to invest in supporting modifications, the end result is a reliable, high‑powered daily driver or weekend track weapon. For those ready to take the leap, this turbo platform offers excellent value and proven headroom.

For further reading on Holset turbo specifications, visit Holset's official site. Community resources such as Genesis G70 Forums provide installation tips and tuning advice from experienced owners. Parts and pre‑assembled turbo kits are available from vendors like LAP3 and BTR Racing.