Tools and Materials Needed

Before beginning this installation, assemble the following tools and materials. Having everything on hand before you start will prevent unnecessary delays and ensure a smooth workflow.

  • Complete socket set (metric and SAE, 3/8-inch and 1/2-inch drive)
  • Combination wrenches (metric and SAE, 10mm through 22mm)
  • Screwdrivers (flathead and Phillips, multiple sizes)
  • Torque wrench (capable of reading in ft-lb and in-lb)
  • Boost gauge and vacuum line kit
  • Intercooler piping kit (2.5-inch or 3-inch, depending on setup)
  • Silicone couplers and T-bolt clamps (various sizes to match piping)
  • Exhaust gaskets (turbo-to-manifold, downpipe-to-turbo, and v-band gaskets if applicable)
  • Oil feed line (braided stainless steel recommended) and fittings
  • Oil drain line and gasket or o-ring
  • Turbocharger mounting hardware (studs, nuts, lock washers)
  • Wastegate actuator and linkage (if separate from turbo)
  • Boost controller (manual or electronic)
  • RTV silicone gasket maker (high-temp, oil-resistant)
  • Thread locker (medium-strength, blue)
  • Shop towels and brake cleaner
  • Safety glasses and mechanic gloves

Preparation and Safety

Proper preparation is critical to a successful turbo installation. Park the vehicle on a level, solid surface and allow the engine to cool completely. Disconnect the negative battery terminal and secure it away from the post. Drain the engine oil and replace the oil filter if the oil change interval is near. Clean the engine bay around the turbo area with degreaser to prevent debris from entering open ports during the swap. Gather all tools and lay out the new turbo and components for visual inspection.

Work in a well-ventilated area and keep a fire extinguisher rated for Class B and C fires nearby. Allow adequate lighting to clearly see all fasteners and connections. If possible, use a lift or sturdy ramps to access the underside of the vehicle without compromising stability.

Understanding Compound Turbo Systems

A compound turbo system uses two turbochargers in series to achieve higher boost pressure and a wider power band than a single turbo can provide. The smaller high-pressure turbocharger feeds compressed air into the larger low-pressure turbocharger, which then compresses it further before it enters the engine. The BorgWarner S300SX3 is typically used as the high-pressure unit in a compound setup on diesel engines, though it can serve as the low-pressure unit depending on the specific build. The S300SX3 features a 63mm compressor wheel and a 68mm turbine wheel with a divided inlet housing, providing excellent flow capacity and quick spool characteristics.

When installing the S300SX3 as part of a compound system, you must consider the piping between the two turbos, the wastegate configuration for the high-pressure unit, and the overall air routing. The high-pressure turbo (S300SX3) draws air from the low-pressure turbo’s compressor outlet, compresses it further, and sends it through the intercooler to the engine. The wastegate on the high-pressure turbo controls boost pressure by diverting exhaust flow away from its turbine wheel when the target boost is reached.

Step 1: Remove the Existing Turbocharger System

If your vehicle already has a turbo system installed, begin by removing it completely. Start by disconnecting the intake tube from the air filter housing to the turbo inlet. Remove the intercooler piping, noting the routing and orientation of each section for reinstallation reference. Label each pipe and coupler with masking tape to avoid confusion later.

Remove the exhaust downpipe from the turbo outlet, supporting it as you loosen the bolts. Disconnect the oil feed line at the top of the turbocharger and the oil drain line at the bottom. Have a drain pan ready to catch residual oil. Carefully unbolt the turbocharger from the exhaust manifold. Use a penetrating oil on rusted or stubborn fasteners and allow it to soak for several minutes before attempting removal. Inspect the manifold mounting surface for flatness and clean off any old gasket material with a razor blade and brake cleaner. Remove all old gaskets and verify that no debris falls into the exhaust ports.

Step 2: Install the BorgWarner S300SX3 Turbo

Position the S300SX3 turbo onto the exhaust manifold studs or bolts. Ensure the oil drain flange faces downward at an angle that allows gravity-assisted oil return to the engine block. Install the new gasket between the turbo and manifold. Torque the mounting nuts or bolts to the manufacturer’s specification, typically in the range of 35-45 ft-lb for M10 studs. Use thread locker on the fasteners to prevent loosening from vibration.

If your compound setup uses a divided inlet turbine housing, ensure the wastegate porting is correctly aligned. Install the wastegate actuator and connect the linkage arm to the wastegate valve. Adjust the actuator rod length so that there is no preload on the wastegate valve when closed, but the rod fits snugly onto the arm. Secure the actuator bracket to the compressor housing or a nearby rigid mounting point.

For compound systems where the S300SX3 is the high-pressure unit, mount the secondary (low-pressure) turbocharger in its designated location, typically in the exhaust stream downstream of the high-pressure turbo. Connect the exhaust piping between the two turbos using heavy-duty v-band clamps or bolted flanges. The high-pressure turbo’s turbine outlet feeds into the low-pressure turbo’s turbine inlet. Use high-temperature exhaust gaskets at all flanged connections.

Step 3: Oil Feed and Drain Connections

The oil feed line delivers pressurized oil from the engine block to the turbocharger center housing. Use a braided stainless steel line with the correct fittings for both the block and the turbo. The feed line typically uses a -4 AN or -6 AN fitting. Connect the feed line to the top port on the turbo center housing, using a crush washer or copper washer for a leak-proof seal. Torque the feed line fitting to 15-20 ft-lb.

The oil drain line must be routed downward at a continuous slope with no dips or kinks that would allow oil to pool. Use a -10 AN or -12 AN line for the drain. Connect the drain flange to the bottom of the turbo center housing, using a new gasket or o-ring. Route the drain line to the oil pan or timing cover drain port. Ensure the drain line does not contact any hot surfaces or moving parts. Secure the line with clamps or zip ties as needed. After connecting all oil lines, rotate the turbo compressor wheel by hand to verify smooth rotation and that no binding or interference is present.

Step 4: Install the Intercooler and Piping

For a compound turbo system, the intercooler is typically located after the low-pressure turbo’s compressor outlet. However, in some configurations, an intercooler may be placed between the high-pressure and low-pressure turbochargers (interstage cooling). Verify your system design before routing piping.

Install the intercooler core in a location with good airflow, such as in front of the radiator or in the lower bumper area. Use silicone couplers and T-bolt clamps to connect the compressor outlet of the low-pressure turbo to the intercooler inlet. Connect the intercooler outlet to the high-pressure turbo’s compressor inlet. From the high-pressure turbo’s compressor outlet, route piping to the engine intake manifold. Use smooth, mandrel-bent piping to minimize flow restriction.

Cut the silicone couplers to length as needed, ensuring they overlap the pipe ends by at least 1.5 inches. Tighten the T-bolt clamps evenly to 8-10 ft-lb, or according to the clamp manufacturer’s recommendation. Check all connections for security by pulling on each pipe section. Avoid sharp bends near the turbo outlets to prevent flow separation and pressure loss.

Step 5: Exhaust System Configuration

The exhaust system must accommodate the compound turbo arrangement. The high-pressure turbo (S300SX3) exhaust outlet connects to the low-pressure turbo inlet via a crossover pipe. Use a flexible exhaust section or bellows to absorb thermal expansion and vibration. Install the downpipe from the low-pressure turbo outlet to the vehicle’s existing exhaust system. Use a v-band clamp or flanged connection with a high-temperature gasket.

Ensure the wastegate dump tube from the high-pressure turbo is routed back into the exhaust downstream of the low-pressure turbo. This prevents unmetered exhaust from causing boost control issues. Weld a bung into the downpipe for a wideband oxygen sensor if you plan to tune the fuel mixture. Check all exhaust connections for leaks by running the engine and listening for ticking or whistling sounds after installation. Tighten any loose clamps or bolts.

Boost Control and Wastegate Setup

Proper boost control is essential for a compound turbo system. The wastegate on the high-pressure turbo regulates boost pressure by controlling the amount of exhaust gas flowing through its turbine wheel. Install a boost controller in the pressure signal line between the compressor outlet and the wastegate actuator. A manual boost controller allows adjustment of boost pressure by bleeding a small amount of pressure from the signal line, while an electronic boost controller offers more precise control and can be adjusted from the driver’s seat.

For a compound system, set the high-pressure turbo’s wastegate spring pressure to achieve the desired total boost. For example, if the total desired boost is 60 psi and the low-pressure turbo contributes 30 psi, set the high-pressure wastegate to regulate at approximately 30 psi (relative to the low-pressure turbo’s output). Verify this calculation matches your specific system design. Adjust the boost controller only after the engine is fully warmed up and all systems are verified leak-free.

Step 6: Reconnect Intake and Exhaust Systems

Reconnect the intake air ducting from the air filter to the low-pressure turbo compressor inlet. Use a dry-type high-flow air filter to minimize restriction. Install the intake air temperature sensor if equipped. Reconnect the exhaust system from the low-pressure turbo outlet to the vehicle’s exhaust pipe, using new gaskets at all connections. Tighten all clamps and bolts to specification. Double-check that no clearance issues exist between the piping and other engine components, especially the fan, belts, and steering shaft.

Step 7: Install Boost Gauge and Monitoring Equipment

Mount a boost gauge in a location visible while driving, such as the A-pillar pod or in the dash. Connect the gauge’s vacuum/pressure line to a boost reference source on the intake manifold or the compressor outlet piping. Use a nylon or silicone line between 1/8-inch and 1/4-inch inner diameter. Route the line away from heat sources and sharp edges. If using an electronic boost gauge, connect the power wire to a switched 12V source and the ground wire to a clean chassis ground. Install a wideband air-fuel ratio gauge if tuning the fuel system to monitor air-fuel ratio under boost.

Step 8: Start the Engine and Perform Initial Checks

Before starting the engine, prime the oil system by disconnecting the spark plugs or fuel injectors and cranking the engine for 10-15 seconds. This allows oil to reach the turbo bearings without load. Reconnect the ignition or fuel system. Start the engine and let it idle. Immediately listen for unusual noises, such as grinding, whistling other than normal turbo spool, or exhaust leaks. Check the boost gauge for a reading of near zero at idle.

Inspect all oil connections for leaks while the engine runs. Look at the oil feed line, drain line, and drain flange for any signs of dripping. Inspect the coolant lines if your S300SX3 is water-cooled. Check intercooler piping connections for air leaks by listening for hissing sounds. Use a smoke machine or a soap-and-water solution to detect leaks at connections. Let the engine reach full operating temperature, then shut it off and check all fluid levels again.

Tuning Considerations

After installing the compound turbo system, the engine’s fuel delivery and timing must be adjusted to match the increased airflow. Without proper tuning, the engine can run lean, causing high exhaust gas temperatures and potential damage. Use a wideband oxygen sensor and an electronic tuning tool compatible with your engine management system. Adjust fuel tables to target an air-fuel ratio of approximately 12.0-12.5:1 under full-throttle boost for diesel engines, and 11.5-12.0:1 for gasoline engines. Adjust ignition timing to avoid detonation, especially under high boost conditions. If you are not experienced with engine tuning, hire a professional tuner to calibrate the system on a chassis dynamometer.

Common Mistakes to Avoid

Several common errors can compromise the performance and reliability of your compound turbo installation. Using undersized oil drain lines causes oil to back up in the center housing, leading to seal failure and smoke. Always use a drain line at least -10 AN with a continuous downward slope. Routing the oil feed line too close to the exhaust manifold will cook the oil and cause coking. Use heat shielding or wrap on the feed line where it passes near hot surfaces. Neglecting to properly torque the turbo fasteners can cause gasket failure and boost leaks. Always use a torque wrench and follow the manufacturer’s specifications. Overlooking wastegate preload adjustment can result in inconsistent boost control. Verify the wastegate arm has zero preload when the valve is closed.

Final Road Test and Verification

Take the vehicle on a test drive under light load first. Gradually increase throttle and monitor the boost gauge, air-fuel ratio, and exhaust gas temperature if equipped. Verify that boost pressure builds smoothly without spikes or hesitation. The boost gauge should respond to throttle input and reach the target boost level as the wastegate regulates. Listen for any unusual sounds from the turbochargers, such as rattling or scraping. Check for smoke from the exhaust at idle and under acceleration. Blue smoke indicates oil burning, which may be caused by a drain back issue or turbo seal failure. Black smoke indicates excessive fuel delivery, which should be addressed with tuning adjustments.

After the test drive, park the vehicle and let it cool. Recheck all fluid levels, especially engine oil. Inspect all connections for tightness, as heat cycling can loosen fasteners. Re-torque any connections that feel loose. Check intercooler piping clamps to ensure they have not backed off. Confirm that no fluid leaks have developed. If everything is satisfactory, the installation is complete and the engine can be operated normally, but continue monitoring the system closely for the first few hundred miles to ensure reliability.

Maintenance Tips for Long Service Life

To maximize the service life of your BorgWarner S300SX3 and the compound turbo system, follow these maintenance practices. Change the engine oil and filter every 3,000 to 5,000 miles, or more frequently under heavy use. Use a high-quality diesel or synthetic oil with the viscosity recommended by the turbo manufacturer. Allow the engine to idle for 30-60 seconds before shutdown to cool the turbo bearings and prevent oil coking. Inspect all boost pipes and couplers for cracks or signs of leakage every oil change. Check the wastegate actuator and linkage for free movement and adjust as needed. Clean the air filter regularly and replace it at the manufacturer’s recommended interval. A dirty filter restricts airflow and forces the turbo to work harder, reducing efficiency and increasing wear.

Conclusion

Installing a BorgWarner S300SX3 compound turbo system is a substantial upgrade that can dramatically improve your vehicle’s power output and drivability when executed correctly. By following the detailed steps outlined in this tutorial, you can achieve a reliable installation that delivers the performance gains you expect from a quality compound turbo setup. Take your time with each step, verify all connections and clearances, and invest in professional tuning to maximize the system’s potential. With proper installation and maintenance, the S300SX3 will provide years of consistent performance and high-boost capability.