Introduction: Unlocking the Full Potential of Your BMW M4

The BMW M4, equipped with the legendary S55 inline-six engine, is a formidable machine straight from the factory. However, for enthusiasts seeking serious power gains, the stock turbochargers quickly become a bottleneck. The Pure Turbos Stage 2 Turbo upgrade is one of the most popular and proven modifications to transform your M4 into a genuine high-horsepower performer. This comprehensive guide details the installation process, critical preparation steps, tuning requirements, and what you can expect in terms of boost and power gains. Whether you are a seasoned DIY mechanic or a shop technician, following this guide will help ensure a successful installation and long-term reliability.

What You Need Before You Start

Proper preparation prevents poor performance. Before you begin, gather all components, tools, and consumables. Having everything on hand will save hours of frustration.

Essential Components and Parts

  • Pure Turbos Stage 2 Turbo Kit – Ensure you have the correct kit for your M4 (model year 2014–2020). The kit typically includes upgraded compressor wheels, billet turbo housings, and wastegate actuators.
  • New OEM Gasket and Seal Kit – Intake manifold gaskets, exhaust manifold gaskets, turbo-to-downpipe gaskets, and valve cover gaskets. Do not reuse old gaskets; leaks after installation are a common issue.
  • High-Quality Coolant and Engine Oil – Use BMW-approved coolant (e.g., BMW Coolant Antifreeze) and SAE 5W-30 or 0W-40 full synthetic oil.
  • Turbo Oil Feed and Return Lines – While the stock lines often can be reused, high-mileage cars may benefit from replacement. Some Stage 2 kits include braided stainless lines.
  • Boost Gauge and OBD Monitor – Highly recommended for monitoring boost pressure and IATs during initial testing.

Tools and Shop Equipment

  • Metric socket set (8mm to 19mm) with extensions
  • Torx and E-Torx sockets (E10, E12, E14)
  • Torque wrench with ranges from 10 Nm to 120 Nm
  • Jack and safety jack stands (minimum 3‑ton capacity)
  • Radiator and intercooler fluid catch pans
  • Pick tool set for O‑ring removal
  • Drift punch and mallet (for stubborn turbo alignment)
  • Brake cleaner and shop towels
  • Video recording device or labelled zip ties for hose routing reference

Preparing Your M4 for Installation

Thorough preparation is the foundation of a smooth turbo swap. Follow these steps in order to access the stock turbos safely.

Step 1: Park and Disconnect the Battery

Park the car on a level surface and allow the engine to cool completely. Disconnect the negative battery terminal in the trunk to prevent any accidental electrical shorts or airbag deployment.

Step 2: Drain Coolant and Remove the Front Bumper

The S55 engine uses a complex cooling circuit. Drain the coolant from the radiator petcock and remove the lower air duct. Remove the front bumper by releasing the clips on the upper panel, the wheel well liner screws, and the lower splash shield. Set the bumper aside with care to avoid scratching the paint.

Step 3: Remove the Charge Pipes and Intercooler

Disconnect the charge pipes from the intercooler and throttle body. Remove the intercooler itself—this provides more room to work from below and also allows you to inspect the condition of the intercooler core. Consider upgrading to a larger aftermarket intercooler if you plan to push higher boost.

Removing the Stock Turbochargers

The S55 features twin turbos, but the process for the driver and passenger side is similar. Plan to replace both turbo units simultaneously, even if only one is damaged, as the labor cost is the same.

Step 1: Disconnect Intake and Exhaust Plumbing

Unbolt the intake air boxes, air filters, and intake ducts. Loosen the V‑band clamps connecting the turbo outlets to the downpipes. Remove the downpipes—this may require soaking the fasteners with penetrating oil if they are corroded. Next, unbolt the exhaust manifold heat shields and then the manifold itself from the head.

Step 2: Unplug Sensors and Electrical Connectors

Carefully disconnect the turbo wastegate actuators, diverter valve connectors, and oxygen sensors. Use a flathead screwdriver to release the clip on each connector.

Step 3: Remove the Oil and Coolant Lines

Place a drain pan under the turbo area. Unbolt the oil feed line from the turbo and the oil return line from the oil pan (you may need to access from below). The coolant lines are clamped with spring clamps; release these and drain any residual fluid.

Step 4: Unbolt the Turbo from the Manifold and Engine

Using an E14 Torx socket, remove the three nuts securing each turbo to the exhaust manifold. Gently rock the turbo back and forth to break any carbon seals. Lift the turbo out of the engine bay. Repeat for the opposite side.

Installing the Pure Turbos Stage 2 Turbochargers

Installation is the reverse of removal, but with critical attention to alignment, torque, and cleanliness. Contaminants inside the turbo will lead to premature failure.

Step 1: Prepare the Mounting Surfaces

Clean the exhaust manifold mating surfaces with a wire brush and make sure they are flat. Install new gaskets. Lightly lubricate the turbo oil feed threads with antiseize compound.

Step 2: Position and Secure the Turbos

Place the Pure Turbos Stage 2 unit into position, ensuring the oil drain port points downward. Hand-start the bolts and then torque the manifold nuts to 35 Nm (26 ft‑lb). Tighten the oil feed line to 25 Nm and the coolant banjo bolts to 20 Nm.

Step 3: Reconnect Wastegate Actuators and Sensors

The upgraded wastegate actuators on the Stage 2 turbos may have longer rods. Adjust the rod length so that the wastegate flap is fully closed at rest but can be opened with minimal preload. Use a duty‑cycle test in your tuning software later to verify proper operation. Reattach all electrical connectors and secure them with zip ties away from heat sources.

Step 4: Reassemble Exhaust and Intake Circuitry

Install the downpipes with new gaskets and tighten the V‑band clamps to the specified torque. Reattach the heat shields, charge pipes, and intercooler. Torque all clamps evenly to avoid boost leaks. For the intake side, reinstall the air boxes and intakes.

Finalizing the Installation

After the turbos are physically in place, complete the reassembly of the front of the car.

Step 1: Refill Coolant and Oil

Refill the engine cooling system with the proper coolant mixture. Use an appropriate vacuum fill tool if available to reduce air pockets. Refill the engine oil with 6.5 liters (for the S55) of a high‑quality full synthetic oil. Do not use additives.

Step 2: Reinstall Front Bumper and Splash Shields

Align the bumper carefully, pressing it into the side brackets, and secure all screws and clips. Reattach the wheel well liners and lower splash shield.

Step 3: Connect Battery and Perform a Boost Leak Test

Reconnect the battery. Before starting the engine, perform a boost leak check by pressurizing the intake system to 15 psi. Use soapy water to identify any leaks at joints. This step is often overlooked but is essential for consistent boost and preventing lean mixtures.

Tuning and Calibration: The Crucial Last Step

Installing the Pure Turbos Stage 2 hardware without a proper tune is not only ineffective but dangerous. The larger turbos flow significantly more air, exceeding the ability of the stock MAF and fuel system. You must pair the installation with a custom tune from a reputable platform.

Flash Tuning Options

Two popular tuning solutions for the S55 are Bootmod3 and MHD. Both offer off‑the‑shelf Stage 2 maps that are calibrated for the Pure Turbos, but a dyno tune by a professional will maximize power and safety. Expect your tuner to adjust fuel tables, boost target, VANOS timing, and cold‑start sequences.

Fuel Requirements

To safely run the additional boost, use 93 octane (RON 98) or higher. If you plan to push beyond 550 whp, consider ethanol blends (E30–E50) with upgraded HPFP or auxiliary port injection.

Testing and Break-In

Resist the temptation to immediately floor the throttle. A gradual break‑in process ensures the turbo bearings and seals seat correctly.

  • Initial Startup: Start the engine and let it idle for 3–5 minutes. Check for oil leaks, coolant leaks, and unusual noises. Monitor the coolant temperature gauge.
  • First Drive: Take a short 10‑minute drive keeping boost below 8 psi. Vary the RPMs but avoid sustained high loads.
  • Boosting Up: After 50 miles, gradually increase boost to full target using your tuning interface. Log data for any knock or excessive IATs.
  • Full Shakedown: Once the engine has accumulated 200 miles, perform a few wide‑open throttle pulls from third gear. Verify that boost hits the target level (typically 20–24 psi on Stage 2) and that fuel trims are within 5% of zero.

Performance Gains and Long‑Term Maintenance

With a proper Stage 2 Pure Turbo setup and custom tune, a bone‑stock S55 engine can produce 550–600 whp (crank 650–700 hp). This is a substantial gain over the factory 425 hp. Torque figures also jump to 550–600 lb‑ft. The upgraded billet wheels provide better spool characteristics and sustain power to the redline.

Maintenance intervals for oil changes should be reduced to 5,000 miles using a high‑quality synthetic. Always allow the turbos to cool down by idling for 30–60 seconds after hard driving. Inspect the intake and charge pipes annually for cracks or oil seepage. Consider a turbo maintenance guide from Pure Turbos for further details.

Conclusion

The Pure Turbos Stage 2 turbo upgrade is a proven path to serious horsepower for your BMW M4. By following this detailed installation guide, preparing adequately, and investing in a professional custom tune, you can enjoy reliable and exhilarating performance. The process requires mechanical skill and patience, but the reward is a car that delivers stunning acceleration and response. If you plan this upgrade, ensure your supporting modifications—exhaust, intercooler, and fuel system—are up to the task. With the right approach, the Stage 2 turbos will transform your M4 into a track‑ready powerhouse.