Introduction: Why Upgrade to a 64mm Twin Turbo?

Swapping a single Holset HX35 turbocharger for a 64mm twin turbo setup in your Ford Powerstroke is one of the most effective ways to unlock serious horsepower and torque gains. The HX35 is a reliable workhorse for stock and mildly modified engines, but its airflow capacity tops out around 400–450 wheel horsepower. A properly sized 64mm twin configuration can support well over 600–700 wheel horsepower while maintaining excellent spool characteristics and lower exhaust gas temperatures (EGTs). Twin turbos also reduce backpressure, improve cylinder scavenging, and make the engine far more responsive both on-road and under heavy load. This guide will walk you through every stage of the installation, from removing the old single turbo to tuning and testing the new twin setup.

Understanding the Upgrade

Holset HX35 vs. 64mm Twins

The Holset HX35 is a single, relatively small turbo used on many 7.3L and early 6.0L Powerstroke engines. While it spools quickly and is very durable, it becomes a restriction when you increase fuel delivery or boost. Twin 64mm turbos, by contrast, provide far more total flow area and higher peak airflow. They allow the engine to breathe freely at high RPM while still delivering strong low-end response because the smaller (or equal-sized) twins can be matched to the engine displacement more efficiently. Many aftermarket kits use a compound or parallel twin configuration; for this guide we assume a parallel sequential setup that replaces the single unit with two equal-size 64mm chargers.

Expected Performance Gains

  • Peak horsepower increase of 50–100% over factory HX35 levels
  • Quicker spool than a comparable single large turbo
  • Lower EGTs under sustained load
  • More usable power across the entire rev range

Pre-Installation Planning

Tools and Materials Needed

Having everything on hand before you start is critical. The original list is a good starting point, but you will also need additional items for a twin conversion.

  • 64mm Twin Turbo Kit (includes turbos, mounting brackets, gaskets, hardware)
  • Oil feed and drain lines (often included with kit, but verify length and fittings)
  • Intercooler piping (Y-pipe, charge pipes, boots, clamps)
  • Silicone couplers and T-bolt clamps
  • Upgraded exhaust manifolds (if not included, you may need adapters or pedestals)
  • Wastegate and boost controller (manual or electronic)
  • Blow-off valve or bypass valve
  • Exhaust gas temperature (EGT) and boost gauge (strongly recommended)
  • Fuel system upgrades (larger injectors, high-pressure oil pump, tuner)
  • Basic hand tools: socket set, wrenches, Allen keys, pry bar
  • Torque wrench with ft-lb and in-lb scales
  • Vehicle lift or heavy-duty jack stands (rated for truck weight)
  • Creeper, penetrating oil, wire brushes, shop rags
  • Safety glasses, gloves, and fire extinguisher

Workspace and Safety

Work in a well-ventilated area with concrete flooring. Disconnect the battery negative terminal at the start. Have a coolant catch pan if your truck uses coolant‑cooled turbos. Allow the engine to cool completely before touching any exhaust components.

Step 1: Preparation

Disconnect Battery and Remove Engine Cover

Unhook both battery terminals to eliminate any risk of shorts. Remove the engine cover (if equipped) and any insulation. On many Powerstroke models, you will also need to detach the air intake duct, the fan shroud, and the upper radiator hose bracket to access the turbo area.

Drain Coolant and Oil (If Required)

If your new turbos use a different cooling circuit than the HX35, you may need to drain the coolant. It’s safer to drain it to avoid messy spills when disconnecting lines. Similarly, if you are replacing oil lines, consider an oil change now so fresh oil flows through the new turbos immediately.

Step 2: Removing the Holset HX35 Single Turbo

Removing the HX35 is straightforward but requires patience with bolts that have been exposed to high heat. Apply penetrating oil to the exhaust manifold nuts and oil line fittings an hour before you begin.

  1. Disconnect all intake piping: Remove the air filter hose, the charge air tube from the intercooler, and any blow-by or CCV tubes attached to the turbo inlet.
  2. Disconnect oil feed line: The oil supply comes from a port on the engine block or a dedicated line. Carefully undo the fitting using a flare wrench if possible.
  3. Disconnect oil drain line: The drain line runs from the bottom of the turbo cartridge into the oil pan. Loosen the drain flange bolts and have a catch pan ready.
  4. Unbolt the turbo from the exhaust manifold: The HX35 is typically mounted on a pedestal. Remove the four or six bolts securing the turbo housing to the manifold. You may need to wiggle the turbo free.
  5. Remove the exhaust manifold (if necessary): Some twin kits require a different manifold or a Y‑pipe that replaces the single outlet. If so, unbolt the manifold from the cylinder head. Note the bolt pattern and use new gaskets.
  6. Inspect and clean: Once the old turbo and manifold are off, clean the mounting surfaces thoroughly. Check for cracks or warping. This is also a good time to replace any deteriorated hoses or wiring in the area.

Step 3: Installing the 64mm Twin Turbo Setup

Mounting the New Turbos

Lay out the new twin turbo kit and identify the left and right units (they are often identical but may have different inlet orientations). Install the provided mounting brackets onto the engine block or cylinder head according to the manufacturer’s instructions. Use thread lock on all bolts and torque to spec—typically 40–50 ft-lb for M10 bolts. Place each turbo onto its bracket and secure with the supplied fasteners. Ensure the turbine housings align properly with the exhaust ports.

Connecting the Exhaust System

Most 64mm twin kits use a divided exhaust manifold or a Y‑pipe that splits into two separate runners. Attach the exhaust manifolds to the cylinder heads with new gaskets and torque to 25–30 ft‑lb. Then connect the remaining exhaust piping from the turbo outlets to the rest of the exhaust system. A wastegate is often required to prevent overboost; install it in the crossover pipe or on the manifold before the turbos.

Routing Oil Feed and Drain Lines

Each turbo needs a dedicated oil feed line. Use the existing block port if it has two outlets, or install a T‑fitting. Braided stainless lines are preferred for heat resistance. Connect the feed to the top of each turbo cartridge. The drain lines should gravity feed back to the oil pan; they should be as short and straight as possible, with a gentle downward slope. Secure all line connections with proper crush washers or O‑rings. Do not reuse old line gaskets.

Intercooler and Charge Piping

With twin turbos, you will route the discharge air from each compressor outlet into a common charge pipe before the intercooler (or after, depending on the kit). Use the supplied silicone couplers and T‑bolt clamps. Verify there is adequate clearance between the pipes and the fan, radiator, and inner fenders. If the kit includes blow‑off valves, mount them on the cold side piping. Test fit everything loosely, then tighten all clamps evenly.

Boost Control and Wastegate Setup

Set the wastegate to open at your target boost level (e.g., 35–40 psi for a 7.3L Powerstroke). Connect the boost signal line from the intake manifold to the wastegate actuator. If using a manual boost controller, install it in the signal line. Electronic boost controllers offer more precise tuning and safety features.

Step 4: Fueling and Tuning Considerations

A 64mm twin turbo setup dramatically increases airflow, which means the stock fuel system will quickly run out of capacity. Before or during the turbo installation, you should upgrade:

  • Injectors: At least 80% over stock (e.g., 160cc/100% nozzles for 7.3L)
  • High-pressure oil system: Increased oil volume via a modified HPOP or dual pumps
  • Fuel pump: Higher flow electric pump for 6.0L engines
  • Chipped / programmed ECU: Custom tuning is mandatory. A generic tune will not handle the twin turbos’ airflow and can cause detonation. Work with a reputable Powerstroke tuner who can adjust fuel tables, timing, and wastegate strategy.

Install an accurate EGT probe in the exhaust manifold runner closest to the cylinder #8 on 7.3L engines. Target peak EGTs below 1250°F under heavy throttle. A boost gauge is also essential—you want to see steady pressure with no oscillation.

Step 5: Final Assembly and Testing

Reinstall Removed Components

Put back the fan shroud, radiator hose brackets, intake duct, and engine cover. Tighten all intercooler tube clamps. Reconnect the battery.

Check for Leaks

Before starting, pour a few ounces of engine oil into each turbo oil feed line to pre‑lubricate the bearings. Then start the engine and let it idle. Listen for air whistles (boost leaks) and watch for oil drips around the turbo seals and drain lines. Use a smoke machine or soapy water to check charge pipe connections.

Initial Test Drive

Once the engine reaches operating temperature, take the truck for a gentle test drive. Accelerate slowly, then gradually increase throttle. Monitor boost, EGT, and oil pressure. If the engine stumbles, runs rough, or shows excessive smoke, you need to adjust tuning or check for boost leaks. After 20 minutes of easy driving, let the engine cool, then re‑torque all the exhaust manifold bolts and turbo mounting bolts.

Final Performance Verification

On a safe stretch of road, perform a wide‑open throttle pull from 2,000 to 3,500 RPM. You should see boost climb smoothly to the wastegate setting and EGTs stay under 1300°F. If the truck feels laggy, the turbos may be mismatched or the wastegate set too high. A professional dyno tune will extract the maximum power safely.

Maintenance Tips for Your Twin Turbo Setup

Keep your investment healthy with these ongoing tasks:

  • Change engine oil every 3,000–5,000 miles using a high‑quality diesel oil (e.g., 15W‑40).
  • Inspect silicone couplers annually for cracking.
  • Listen for bearing noise from the turbos; a chirping or grinding sound indicates wear.
  • Clean or replace the air filter regularly—twin turbos draw more air.
  • Check wastegate actuator movement periodically to prevent sticking.

Conclusion

Upgrading from a Holset HX35 single turbo to a 64mm twin setup in your Ford Powerstroke is a major power adder that rewards careful planning and execution. By following this expanded guide, you’ll avoid common pitfalls such as oil starvation, boost leaks, or insufficient fuel delivery. The result is a truck that pulls harder, spools faster, and handles heavy loads with lower EGTs. For detailed turbo selection advice, visit the Powerstroke.org forums or check respected suppliers like Diesel Emission Parts for complete twin kits. Always invest in proper tuning from a professional such as those at Gearhead Fabrications to maximize reliability. Enjoy the new power—and drive safely.