Introduction to Duramax Turbo Upgrades

The Duramax diesel engine has earned its reputation as one of the most capable and durable powerplants in the heavy-duty pickup market. Whether you drive an LB7, LLY, LBZ, LMM, or L5P, the turbocharger plays a central role in how the engine breathes, spools, and delivers power. Upgrading your turbocharger—whether it’s a drop-in stock replacement or a larger ATS 66mm unit—can transform throttle response, towing capability, and overall horsepower.

This guide provides a complete, shop-tested walkthrough for removing the factory turbo and installing either a stock-replacement or an ATS 66mm turbocharger on a Duramax. You’ll find specific torque values, common pitfalls, and pro tips that go far beyond the basic steps. By the end, you’ll have the confidence to tackle this job in your own garage or shop.

For background on why Duramax owners choose aftermarket turbos, check out Diesel Power Products. For torque specifications always refer to your vehicle’s service manual.

Choosing the Right Turbocharger: ATS 66mm vs. Stock Upgrade

Before we dive into the wrenching, it’s critical to select the right turbo for your goals and budget.

Stock Replacement Turbo

If your factory turbo has failed (worn bearings, stuck vanes, oil leaks) and you want to restore original performance, a stock replacement is the simplest route. It bolts directly in, requires no tuning changes, and maintains factory spool characteristics. However, it offers no power increase beyond what the truck left the assembly line with.

ATS 66mm Turbo Upgrade

The ATS 66mm is a popular aftermarket upgrade designed for a noticeable boost in airflow and horsepower without sacrificing drivability. It features a larger compressor wheel, a ported housing, and often a redesigned wastegate. Key benefits:

  • ~20–40% more airflow over stock
  • Improved towing and passing power
  • Works with minor tuning adjustments
  • Direct fit for most LB7–LMM engines (requires some adapter parts for L5P)

Keep in mind that the ATS 66mm may require a custom tune to fully realize its potential and to avoid overboost or smoke. Consult a reputable tuner like Duramax Tuner for calibration advice.

Tools and Materials You’ll Need

A complete list is essential because once you start the job, running to the parts store will waste hours. Beyond the basics listed in the original guide, here is an expanded inventory:

Hand Tools:

  • 3/8″ and 1/2″ drive socket sets (metric, deep and shallow)
  • Combination wrench set – 8mm to 19mm
  • Torque wrench – 0–250 ft-lb range
  • Flathead and Phillips screwdrivers (medium and large)
  • Pry bar (small, for aligning mounts)
  • Pick set (for removing O-rings)
  • Brake cleaner or degreaser

Specialty Items:

  • Turbo pedestal gasket kit (includes oil feed and drain gaskets)
  • New intake and exhaust gaskets
  • Anti-seize compound (for exhaust bolts)
  • Threadlocker (medium strength)
  • New V-band clamp (if old one is corroded)
  • Catch pan or drain pan
  • Shop towels or rags

Liquids:

  • Fresh engine oil (meeting Duramax spec, e.g., CJ-4 or CK-4)
  • New oil filter
  • Coolant (DEX-COOL or equivalent, according to your model year)

Preparation Steps – Safety First

Preparation is where most successful installations are won or lost. Follow these expanded steps to set yourself up for a smooth install:

  1. Disconnect the negative battery terminal – This prevents accidental starter engagement and protects the ECU.
  2. Drain the engine oil and coolant – Remove the oil drain plug and open the radiator petcock. Drain at least 50% of the coolant so you don’t get a bath when disconnecting hoses.
  3. Remove the engine cover – On LMM and newer trucks, the cover may hide access to top-side bolts. Set it aside.
  4. Take reference photos – Snap clear images of the turbo inlet, outlet, wastegate linkage, oil feed line, and coolant lines. This is your blueprint for reassembly.
  5. Clean the work area – Blow or wipe away dirt and debris from around the turbo area to prevent contamination during removal.
  6. Support the vehicle – Use jack stands if you need to access underside bolts; never rely on a jack alone.

Removing the Old Turbocharger

This part of the job requires patience. Exhaust bolts on older Duramax engines are notorious for seizing. Soak them with penetrating oil the night before if possible.

Step 1: Disconnect Intake and Exhaust Pipes

Loosen the clamps on the intake tube (from the air filter housing) and the intercooler pipe. Remove the entire intake hose assembly. For the exhaust side, unbolt the exhaust downpipe from the turbo outlet and the exhaust manifold. On some models, you may need to unbolt the up-pipe from the manifold as well.

Step 2: Disconnect the Wastegate Actuator

The wastegate actuator rod is connected to the turbo housing. Use a small screwdriver or a pick to remove the cotter pin or clip. Carefully pull the rod free. Mark the orientation so you can reinstall it in the same position.

Step 3: Unbolt the Turbo from the Manifold

Remove the bolts that secure the turbo to the exhaust manifold. These are usually 13mm or 15mm. You may also need to unbolt the turbo pedestal from the block (three bolts on most Duramax engines). Keep track of any washers or spacers.

Step 4: Disconnect Oil and Coolant Lines

The oil feed line is a small metal tube that connects to the top of the turbo. The drain line is a larger diameter hose (or metal pipe) that returns oil to the pan. Place a catch pan underneath to collect residual oil. Also, disconnect the two coolant lines (supply and return) – these often have 10mm banjo bolts. Plug the lines with shop rags to keep dirt out.

Step 5: Remove the Turbo

With all connections freed, carefully lift the turbo out of the engine bay. It is heavy (approximately 20–30 lbs), so use both hands. Rotate it as needed to clear the firewall. Set it on a clean workbench.

Installing the New Turbocharger

Now the real work begins. Clean all mating surfaces thoroughly before installing the new unit.

Step 1: Prepare the New Turbo

Inspect the ATS 66mm or stock replacement turbo for any shipping damage. Rotate the compressor wheel by hand – it should spin freely with minimal resistance. Apply a small amount of anti-seize to the exhaust side mounting bolts.

Step 2: Install New Gaskets and Seals

Place a new gasket on the exhaust manifold flange. Also replace the O-ring or gasket on the turbo pedestal (oil drain area). Never reuse old gaskets – they will leak.

Step 3: Position and Bolt the Turbo in Place

Lower the new turbo onto the manifold studs or bolts. Install the mounting bolts and torque them to the specification in your service manual (typically 35–45 ft-lb for manifold bolts and 18–22 ft-lb for pedestal bolts). Use a torque wrench.

Step 4: Reconnect Oil and Coolant Lines

Reattach the oil feed line using a new crush washer if applicable. Torque to 15–20 ft-lb. Connect the oil drain line and tighten the clamp. For the coolant lines, install new washers on banjo bolts and torque to 12–15 ft-lb. Check for interference with other components.

Step 5: Reattach the Wastegate Actuator

Connect the wastegate rod to the actuating arm and secure it with a new cotter pin. Ensure the rod is in the same orientation as the original – many aftermarket turbos have an adjustable rod that must be set to proper preload. Refer to the ATS instructions if you have an adjustable actuator.

Step 6: Torque All Fasteners

Double-check every bolt: turbo-to-manifold, pedestal, oil drain, coolant banjos, and wastegate bracket. Loose bolts will cause exhaust leaks, oil leaks, and poor boost response.

Connecting the Intercooler and Exhaust

With the turbo securely mounted, it’s time to complete the airflow paths.

Upstream: Intake and Compressor Inlet

Attach the intake tube from the air filter box to the turbo compressor inlet. Use a new silicone coupler if your old one is cracked or oil-soaked. Tighten the worm gear clamp securely without overdoing it (hand-tight plus a quarter turn).

Downstream: Intercooler Piping

Connect the intercooler (charge air cooler) pipe from the turbo compressor outlet to the intercooler. Install all clamps and ensure the pipe seats fully inside the coupler. A boost leak here will cost power and fuel economy. Use a boost leak tester later to verify.

Exhaust Connection

Reattach the exhaust downpipe to the turbo outlet. Use a new gasket and apply anti-seize to the studs. Torque the nuts to 30–35 ft-lb. Check that the pipe isn’t stressed or touching the firewall or frame.

Final Steps and Post-Installation Checks

Refill Fluids

Pour fresh engine oil into the crankcase (use the correct weight and quantity). Refill coolant to the proper level, following your Duramax model’s procedure – some require a vacuum fill tool to avoid air pockets.

Reconnect Battery and Prime Oil System

Reconnect the negative battery terminal. Before starting, you can prime the oil system by cranking the engine with the injector harness disconnected (or the fuel relay out) for 10–15 seconds. This forces oil into the turbo bearings before it sees exhaust pressure. Consult your service manual for the specific priming method.

Start and Inspect

Start the engine. It may run rough for a few seconds as the system bleeds air. Let it idle for 5–10 minutes. While idling, inspect around the turbo for any signs of oil, coolant, or exhaust leaks. Listen for unusual noises (whistling beyond normal turbo sound, rattles, or knocking).

Test Drive and Monitor

Take the vehicle for a gentle test drive. Keep boost low (under 20 psi) for the first 50 miles to allow the turbo bearings to break in. After that, perform a few moderate to full-throttle pulls and watch gauges for boost pressure, exhaust gas temperature (EGT), and fuel rail pressure. If you have an aftermarket tune, verify that boost targets are met without excessive smoke.

Break-In Considerations

An ATS 66mm turbo benefits from a break-in period. Avoid sustained high loads for the first 100 miles. Change the engine oil and filter after the first 500 miles to remove any wear particles from the initial seating of bearings and seals.

Tuning Adjustments for the ATS 66mm

While a stock replacement turbo runs fine on factory programming, the ATS 66mm should be paired with a dedicated tune. Without tuning, the engine may overboost (turbo surge), run lean, or produce excessive black smoke. A good tune will adjust fueling and turbo vane position (on VGT models) to match the increased airflow. If you are running a custom ECM tune, work with a tuner who has experience with ATS products. Popular options include ATS Diesel Performance themselves or reputable third-party tuners.

Common Mistakes and How to Avoid Them

  1. Reusing old gaskets or seals – Always replace them. A £10 gasket can save you a weekend of rework.
  2. Overtightening exhaust bolts – Torque specs exist for a reason. Breaking a manifold stud means extraction time.
  3. Forgetting to prime the oil system – Dry starts can destroy a new turbo in seconds.
  4. Ignoring boost leaks – A small leak after the turbo will rob power and increase EGTs.
  5. Not updating the tune – Running a larger turbo on stock programming is like putting a bigger carburetor on a lawnmower engine – it won’t work right.
  6. Skipping the test drive inspection – Driving away without checking for leaks or noises can lead to major damage.

Conclusion

Upgrading your Duramax turbocharger—whether to a fresh stock unit or a performance-oriented ATS 66mm—is one of the most rewarding modifications for power and drivability. The installation process is detailed but straightforward for the home mechanic who has the right tools and a methodical approach. By following the expanded steps in this guide, you can avoid common pitfalls and end up with a boost system that works reliably for years.

Remember to take your time, torque everything properly, and never skip the post-install checks. If you get stuck, online forums like DuramaxForum have a wealth of real-world advice. With your new turbo installed and tuned, your Duramax will be ready to tow, haul, and accelerate with renewed confidence.