Understanding the BorgWarner S300 Upgrade for Your 6.7L Cummins

The BorgWarner S300 turbocharger is a proven aftermarket upgrade for the 6.7L Cummins diesel engine. It offers a significant jump in airflow capacity compared to the stock unit, which directly translates to higher horsepower and torque. Enthusiasts commonly see gains of 100–150 rear-wheel horsepower when the S300 is paired with proper fueling modifications. This upgrade is particularly popular among owners looking for more mid-range and top-end power without sacrificing daily drivability.

The S300 series features a larger compressor wheel, a more efficient turbine housing, and improved journal bearings designed to handle higher boost pressures and exhaust gas temperatures. However, installing this turbo is not a simple plug-and-play procedure. It requires careful preparation, the right tools, and an understanding of how the new turbo interacts with your engine’s fueling, exhaust, and intake systems.

Tools, Materials, and Parts Required

Specialty Tools

  • Torque wrench (3/8" and 1/2" drive) – for manifold and turbo bolts
  • Deep socket set – 10mm to 19mm, with extensions
  • Flare nut wrenches – for oil lines (avoid rounding fittings)
  • Pick set – for removing old gasket material
  • Diesel tuning software (e.g., EFI Live, HPTuners) or handheld programmer
  • Exhaust pyrometer (EGT gauge) – essential for monitoring during test drives
  • Boost gauge – to verify target boost pressures

Installation Kit Contents

  • BorgWarner S300 turbocharger (specify frame: S366, S369, S372 depending on horsepower goals)
  • Turbo mounting bracket and hardware
  • Oil feed line kit (braided stainless steel recommended)
  • Oil drain line kit with gaskets
  • Downpipe adapter (if not using a new downpipe)
  • Gasket set (manifold to turbo, turbo to downpipe, oil drain flange)
  • V-band clamp and O-rings (for turbine outlet)
  • High-temperature silicone sealant (e.g., Permatex ultra copper)

Optional Upgrades

  • Aftermarket exhaust downpipe (3.5" or 4") to reduce backpressure
  • High-flow intake elbow and air filter
  • Upgraded intercooler boots and clamps
  • Larger injectors or CP3 fuel pump (for 150+ HP)

Preparation and Safety

Work Area and Vehicle Prep

Park the vehicle on level concrete, set the parking brake, and disconnect the negative battery cables. Allow the exhaust manifolds and turbo to cool completely—surface temperatures can exceed 400°F even an hour after shutdown. If possible, work with a clean engine bay to reduce dust and debris ingestion during the swap.

Drain the cooling system if your turbo is water-cooled (some 6.7L configurations have water lines to the center cartridge). Also, drain engine oil to avoid spills when removing the oil lines. Have a catch pan ready for residual oil in the lines.

Back-to-Stock or Baseline Tuning

Before installing the S300, ensure your truck is running a safe tune that supports higher airflow. Aggressive timing or fueling maps designed for the stock turbo may cause excessive EGTs and smoke when the new turbo spools faster. Never run high power on the stock tune with a larger turbo—at minimum, use a “valet” or “hot” tune from a reputable diesel tuner. HP Tuners and EFI Live are two popular platforms for 6.7L Cummins tuning. You will also need a custom file from a calibrator experienced with the S300.

Step 1: Removing the Stock Turbocharger

Disconnect Intake and Exhaust

  1. Remove the intake tube from the air filter housing to the turbo inlet.
  2. Unclamp the charge air cooler (CAC) pipe from the compressor outlet on the turbo.
  3. Disconnect the exhaust downpipe from the turbine outlet. If the downpipe bolts are corroded, use penetrating oil and a breaker bar. It is often easier to unbolt the downpipe from the exhaust manifold bracket as well.
  4. Unplug the wastegate actuator electrical connector (if equipped) and note its routing.

Oil Lines and Coolant Hoses

Using flare nut wrenches, disconnect the oil feed line (usually a 1/8" NPT fitting) from the turbo. The oil drain line is typically a 3/4" or 1" hose clamped to the bottom of the turbo cartridge. Loosen the clamps and slide the hose off. If your truck has water lines, clamp them off to prevent coolant loss, then remove them. Cap all open lines to keep debris out.

Remove Exhaust Manifold (If Necessary)

On some 6.7L applications, the stock turbo sits directly on the exhaust manifold. The S300 kit may require the manifold to be removed to replace it with a compatible aftermarket manifold (e.g., Fleece, BD Diesel). Check your kit’s instructions. If removal is needed, unbolt the manifold from the cylinder head (16 bolts or nuts, torque sequence is critical—refer to the shop manual). This is a good time to inspect for cracks and to clean the mounting surface.

Step 2: Preparing the BorgWarner S300 for Installation

Prepping the Oil System

Prime the new turbo bearing cartridge by pouring clean engine oil into the oil feed port while spinning the compressor wheel by hand. This prevents dry startup wear. Apply a thin layer of silicone sealant to the oil drain flange gasket. The drain line must have a slight downward slope to gravity-feed oil back to the pan; avoid any loops or kinks.

Gaskets and Sealants

Install the manifold-to-turbo gasket dry (unless otherwise specified). Many S300 kits use a simple metal gasket with raised beads. Use a high-temp anti-seize compound on the turbo mounting studs and nuts. On the turbine outlet, apply a small amount of copper silicone to both sides of the V-band coupling gasket to prevent exhaust leaks.

Step 3: Installing the New Turbocharger

Mounting the Turbo

  1. If using an aftermarket exhaust manifold, torque it to spec first (typically 32–38 lb-ft on the 6.7L).
  2. Position the S300 so the compressor cover is oriented toward the air intake (usually forward-facing on Dodge Rams).
  3. Thread the mounting studs through the manifold, then slide the turbo onto them. Hand-tighten the nuts, then torque in a cross pattern to 35-40 lb-ft.
  4. Attach the oil drain line using new gaskets. Torque the drain flange bolts to 12-15 lb-ft.

Reconnecting Oil Feed and Coolant

Connect the braided oil feed line to the turbo. The fitting should be snug but not overtightened (use Teflon tape on pipe threads). Rearm coolant lines if applicable, ensuring no leaks. For water-cooled turbos, bleeding air from the circuit is important—leave one clamp loose, start the engine briefly to purge air, then tighten.

Installing the Downpipe

Many S300 upgrades require a new downpipe because the turbine outlet flange size differs from stock. Use the V-band clamp supplied with the kit. Slide the downpipe gasket onto the turbo outlet, align the downpipe, and tighten the V-band to the manufacturer’s torque spec (often 10-12 Nm). If reusing the stock downpipe, you’ll need a reducer adapter.

Intake and Intercooler Hoses

Connect the compressor outlet to the intercooler pipe using a silicone coupler and T-bolt clamps. The S300 uses a 4" compressor inlet, so the intake tube may need a reducer to fit the OEM air box. Alternatively, install a cold-air intake with an open-element filter for better flow. Re-check all connections for tightness.

Step 4: Wastegate and Boost Control

The BorgWarner S300 often has an internal wastegate, but some kits require an external gate (e.g., Tial MVR). If your setup uses an external gate, weld a bung to the exhaust manifold. Connect the wastegate actuator reference line to a boost source—typically a 1/8" NPT tap off the compressor housing or the intake manifold. A boost controller (manual or electronic) is recommended to fine-tune boost levels and prevent overboost. Start with 30–35 psi and adjust after logging EGTs and exhaust backpressure.

Step 5: Tuning and Calibration

Software Loading

Do not attempt to drive the truck without a tune specific to the S300. The larger turbo shifts the air density curve, and the stock ECU will inject fuel at the wrong timing. Flash a custom tune using a dedicated tuner device. Many tuners offer “hot street” calibrations that target 40–45 psi of boost and 2–3 ms injection duration at full load. Have your tuner adjust smoke limits, rail pressure, and injection angle to match the new compressor efficiency.

Monitoring Parameters

Install an EGT probe in the exhaust manifold (pre-turbo) and a boost gauge. During the first test drive, keep EGTs below 1250°F sustained (peaks to 1350°F are acceptable for short bursts). If EGTs rise too quickly, reduce fueling through the tuner or add water/methanol injection. Advanced tuning software like EFI Live allows real-time data logging of boost, MAF, fuel rail pressure, and throttle position. Use this data to dial in your tune safely.

Step 6: Final Checks and Test Drive

Pre-Test Inspection

  • Reconnect battery cables and prime the fuel system (cycle the key three times without starting).
  • Crank the engine until the oil pressure light goes out (disable the fuel pump by pulling the fuse for 15 seconds to dry-fire). This pre-lubes the turbo bearings.
  • Reinstall the fuel pump fuse, start the engine, and let it idle for 2 minutes. Listen for unusual noises like metallic rubbing or a high-pitched whine from the turbo bearing.
  • Check for oil leaks at the feed line, drain, and around the V-band. Also inspect for coolant leaks.

Road Test

Drive gently for 10 minutes with light throttle to let the turbo housing reach normal operating temperature. Then perform a series of gradual accelerations from 30 to 60 mph at 50% throttle while observing boost and EGT. If boost exceeds the wastegate spring pressure (typically 25-30 psi for internal gates), reduce boost controller duty or adjust the reference line. After the test drive, park and inspect for leaks again. Recheck turbo bolts after the first heat cycle—they often loosen slightly.

Conclusion

Installing a BorgWarner S300 turbocharger on your 6.7L Cummins is one of the most effective bolt-on upgrades for serious horsepower gains. With careful installation, proper tuning, and attention to fuel and exhaust modifications, you can realize the full 150+ horse power increase safely. Remember to invest in a quality EGT gauge and spend time dialing in the tune to match the S300’s airflow characteristics. BorgWarner’s official site provides detailed specs for each S300 frame, and forums like Cummins Forum have dedicated build threads where owners share real-world results and troubleshooting tips. With the right preparation, your 6.7L will transform into a high-horsepower workhorse that still tows daily.