Turbo Upgrades Diesel Installation: Installing a Holset Hx40 in Your 6.7l Cummins

Understanding the Holset HX40 Turbocharger for the 6.7L Cummins

The Holset HX40 is a turbocharger originally designed for heavy‑duty diesel applications, known for its ability to move large volumes of air with excellent durability. When replacing the factory variable geometry turbo (VGT) on a 6.7L Cummins with an HX40, you typically choose a non‑VGT, wastegated or non‑wastegated version that delivers a different power curve, better top‑end flow, and often a more aggressive spool characteristic. This swap appeals to owners who have upgraded injectors, CP3 pumps, or are running higher boost levels for racing or towing heavy loads.

Key attributes of the HX40 include a 60mm or 60.5mm inducer compressor wheel, a turbine housing that can be selected for A/R ratio (typically 0.70 or 0.80 for a 6.7L), and a journal‑bearing center section that has proven reliable for hundreds of thousands of miles. Compared to the stock He351ve or S400‑based turbos, the HX40 offers higher peak airflow and simpler plumbing if you eliminate the VGT actuator and electronic controls. Many enthusiasts pair the HX40 with a quality wastegate to control boost creep, especially when running high fuel tunes. For more technical specs, refer to the Holset HX40 aftermarket page.

Preparation for Installation

Before turning a wrench, gather all required parts and tools. A well‑planned installation reduces downtime and prevents common mistakes. Below is a comprehensive checklist.

Required Parts

Holset HX40 turbocharger – core or new unit; verify the correct compressor cover and turbine housing flange for your 6.7L manifold (typically T3 or T4 foot).
Mounting gasket set – includes manifold‑to‑turbo gasket and turbo‑to‑downpipe gasket. Use OEM or high‑temperature graphite gaskets.
Oil feed line – braided stainless steel with the correct fitting sizes (commonly -4 AN) for the HX40 oil inlet.
Oil drain line – -10 AN or similar, with a compatible flange to the turbo center section and a return to the engine block.
Boost tubes and couplers – you may need to fab or purchase an intake tube that mates the HX40 compressor outlet to the intercooler piping. Also required: silicone hoses and T‑bolt clamps.
Wastegate (if using a non‑wastegated version) – external wastegate like a Tial 38mm or Turbosmart, plus a boost reference line.
Exhaust downpipe adapter – match the HX40 turbine outlet (usually 3” V‑band or 4‑bolt) to your existing exhaust system.
Hardware kit – bolts, locking washers, studs (M10 or M8 depending on manifold) and high‑temperature anti‑seize compound.

Tools Required

Socket set (¾″ and ⅜″ drive) with metric and SAE sockets
Torque wrench (capable of 20–80 ft‑lbs range)
Gasket scraper and brake cleaner for cleaning surfaces
Pick‑and‑hook set for removing old gasket material
Oil drain plug removal tool (hex key or Allen socket)
Safety glasses, gloves, and a catch pan for oil and coolant
Jack and jack stands or a lift for easier access

Also consider tuning software or a custom EFI Live/HPTuners tune to take advantage of the new turbo’s flow characteristics. Without recalibrating fuel and timing, the engine may run rich or experience excessive exhaust gas temperatures (EGTs).

Step‑by‑Step Installation Process

1. Remove the Stock Turbocharger

Disconnect the negative battery terminals. Let the engine cool completely to avoid burns. Drain the engine oil (or have a plan to catch oil from the feed line). Then proceed:

Remove the intake air intake tube from the turbo compressor inlet.
Unbolt the exhaust downpipe from the turbine outlet. Support the downpipe with a jack if needed.
Disconnect the oil feed line at the block and turbo. Loosen the banjo bolt on the stock VGT actuator oil supply (if equipped) and remove the VGT actuator wiring harness.
Disconnect the oil drain line (two bolts on the block fitting).
Remove the four or six bolts securing the turbo to the exhaust manifold. Carefully lift the turbo out. It may require wiggling to clear the engine bay.
Inspect the manifold surface for cracks or warping. Clean the mounting face with a scraper and brake cleaner.

2. Prepare the Holset HX40 for Installation

Before installing, perform these checks:

Rotate the compressor wheel by hand – it should spin freely without binding or excessive side play (less than 0.030” axial play is normal).
Apply a thin layer of high‑temp anti‑seize to the threaded holes for the oil feed and drain fittings.
Install the mounting gasket onto the manifold side. Use the correct gasket orientation – many are directional.
If you are using an external wastegate, weld the wastegate flange onto the exhaust manifold or turbine housing inlet pipe. Alternatively, purchase a pre‑cast manifold with a wastegate pad.
Attach the oil feed and drain lines loosely to the turbo – final tightening will happen after mounting.

3. Install the HX40 Turbo on the Manifold

Lift the HX40 into position with a helper or an engine hoist strap. The turbo is heavy (approx. 25–30 lbs). Align the exhaust flange with the manifold studs. Tighten the nuts in a cross‑pattern to the manufacturer’s torque spec – typically 35–45 ft‑lbs for M10 studs. Do not overtorque.

Once the turbo is snug, torque the oil feed line fitting (usually 18–20 ft‑lbs for -4 AN). Use a flare‑nut wrench to avoid rounding.
Torque the oil drain line fiitting (two bolts, 10–12 ft‑lbs). Ensure the drain line angles downward with no kinks.
Reconnect the boost tube from compressor outlet to intercooler. Use silicone couplers and T‑bolt clamps – torque clamps evenly.
Reattach the exhaust downpipe with a new gasket. For V‑band connections, ensure the clamp is fully seated and torqued to spec (about 30‑40 ft‑lbs for 3” V‑band).

4. Install Wastegate and Boost Control

If you are running a non‑wastegated HX40, install an external wastegate. Plumb a boost reference line from the compressor housing to the wastegate actuator. Set the wastegate spring to a desired boost level (e.g., 25 psi for mild tune, 35 psi for high‑power). The exact open pressure depends on your fuel system and tuning. For street use, many owners run a 25‑30 psi spring.

Secure all vacuum/boost hoses with clamps. Test for leaks by pressurizing the system to 20 psi with a hand pump and soapy water.

5. Final Checks and Reassembly

After everything is connected, double‑check:

All oil lines are tight and oriented to allow proper drainage. The drain line must drop continuously from the turbo to the block.
Intake and exhaust connections are leak‑free.
All electrical connectors (e.g., boost pressure sensor, engine block heater) are reconnected if applicable.
Clearance to nearby components (brake lines, fuel lines) – no rubbing under vibration.
Refill engine oil with the correct grade (typically 5W‑40 or 15W‑40 diesel oil).
Reconnect battery and reinstall any removed engine covers (e.g., valve cover).

Tuning and Calibration

The HX40’s different airflow characteristics demand custom tuning. The stock ECM maps are calibrated for the VGT’s variable nozzle and lower airflow. With the HX40, the engine may hit boost much faster (or slower depending on turbine housing A/R). Without recalibration, you risk over‑boost, limp mode, or excessive smoke.

Use a reputable tuner who understands the 6.7L Cummins and can adjust fuel tables, boost limits, and timing. Many owners pair the HX40 with a 50‑60% over injector set and a CP3 pump to deliver enough fuel at high RPM. A good starting point is a tow tune that limits smoke while keeping EGTs under 1350°F. For performance, aim for peak boost between 35–45 psi, but ensure the wastegate and head studs can handle it. Read more about tuning considerations on Cummins Forum discussions.

Troubleshooting Common Installation Issues

Problem	Likely Cause	Solution
Oil leak at drain flange	Incorrect gasket or loose bolts	Replace gasket; tighten bolts to 12 ft‑lbs with threadlocker
Boost creep above desired level	Wastegate too small or not opening fully	Upgrade to 38mm+ wastegate; check boost reference line
Black smoke at idle/low load	Rich fuel mapping or turbo lag	Retune; consider a smaller turbine housing for faster spool
Limp mode (overboost)	ECM sees boost above limit	Update tune with proper boost limit; check wastegate function

If the engine idles rough after startup, bleed air from the fuel system (crank engine with pedal to floor for 10 seconds). Also verify that the oil pressure reaches the turbo within 3 seconds – pre‑oil the turbo by disconnecting the fuel pump relay and cranking the engine for 10‑15 seconds before first start.

Maintenance and Longevity Tips

To maximize the HX40’s service life:

Change engine oil every 5,000 miles or sooner if you tow heavily. Diesel soot breaks down the oil’s additive package, leading to turbo coking.
Use a high‑quality full synthetic oil rated for diesel (CJ‑4 or CK‑4).
Allow the turbo to cool at idle for 30‑60 seconds after a hard run before shutting down. This prevents oil coking inside the center housing.
Inspect boost tubes and couplers annually for cracks or leaks.
Monitor exhaust gas temperature (EGT) with a pyrometer. Keep sustained EGTs below 1400°F. Install a high‑temp exhaust wrap on the manifold to reduce under‑hood heat.

For additional reliability tips, see Garrett Turbo Tech (though not Holset, the principles of oil flow and cooling apply).

Performance Gains and Driving Impressions

After a proper installation and tune, you can expect a noticeable increase in mid‑ to high‑RPM power. The HX40 shines above 2,500 RPM, delivering a strong pulling surge that the stock VGT cannot match. Many owners report a 50‑80 horsepower gain on a mild tune, with EGTs staying manageable. The turbo whistle is also more pronounced – a pleasant side effect for enthusiasts.

Downsides: slower low‑RPM response compared to the stock VGT’s variable geometry. However, a properly selected turbine housing (0.70 A/R for fast spool, 0.80 for top‑end) can improve drivability. Pair with a quality 4‑inch exhaust and cold air intake to maximize gains. For towing, the HX40 works well with a 35‑45 psi spring and a conservative tune, giving strong power without excessive heat.

Conclusion

Installing a Holset HX40 turbocharger in your 6.7L Cummins is a rewarding upgrade that transforms the engine’s power delivery. The key to success lies in thorough preparation, careful installation of oil and exhaust connections, and professional tuning. With the right parts and attention to detail, your Cummins will run stronger, pull harder, and sound better – all while retaining the legendary durability that makes the 6.7L a favorite. Always consult your vehicle’s service manual and a qualified diesel technician if you are uncertain about any step. For further reading, check out Diesel Power Products’ turbo installation guides and the Holset aftermarket support page.