Upgrading Your N55: Installing an HPA 58mm Turbocharger

The BMW N55 engine is a capable powerplant, but for enthusiasts seeking more than the stock output, a turbocharger upgrade is a proven path. The HPA 58mm turbo kit offers a significant jump in airflow and spool characteristics, allowing for 450-550 wheel horsepower when paired with proper supporting mods and tuning. This guide provides a detailed walkthrough of the installation process, covering tool selection, removal of the factory unit, fitting the HPA 58mm turbo, and critical final steps. Whether you’re an experienced DIYer or a shop technician, these steps and tips will help ensure a reliable, high-performance result.

Tools, Materials, and Workspace Preparation

Before lifting the hood, gather everything needed. The HPA 58mm turbo kit includes the turbocharger itself, gaskets, and sometimes upgraded oil and coolant lines. You’ll also need the following items:

Required Tools

  • Socket set with metric sizes (8mm, 10mm, 13mm, 15mm, 18mm are common)
  • Torque wrench (capable of 8-80 Nm / 6-60 lb-ft)
  • Combination wrenches: 10mm, 13mm, 17mm
  • Flathead and Phillips screwdrivers
  • Pry bar or long flathead for separating flanges
  • E-Torx sockets (E10, E12, E14) for BMW-specific bolts
  • Jack and jack stands or lift
  • Oil catch can (recommended to catch residual oil during removal)
  • Coolant drain pan and oil drain pan
  • Line wrench (flare nut) for turbo oil feed line
  • Mirror and flexible inspection camera (helpful for checking rear clearance)

Supplies and Consumables

  • New BMW exhaust manifold gasket
  • New turbocharger inlet and outlet gaskets (often included with HPA kit)
  • New oil return line gasket or O-ring
  • New coolant line O-rings
  • High-temperature anti-seize compound for bolts
  • Thread locker (Loctite 243 medium strength) for critical fasteners
  • 5W-40 or 0W-40 synthetic engine oil (depending on climate and build)
  • BMW-approved coolant mixed 50/50 with distilled water
  • Safety glasses and mechanic’s gloves

Workspace and Safety

Park the vehicle on a level surface, disconnect the battery negative terminal, and allow the engine to cool completely. Hot coolant and oil can cause severe burns. Drain the engine oil and coolant before proceeding. Use a lift or jack stands rated for the vehicle’s weight—never work under a car supported only by a jack.

Step 1: Removing the Factory Turbocharger

Access to the N55 turbo is tight, especially on the rear of the engine. Remove the following components to create working space: engine cover, air intake duct, charge pipe, and the intake manifold (optional but recommended for easier access to the turbo outlet and wastegate). On some N55 applications, removing the upstream catalytic converter or downpipe is also necessary.

Disconnect Intake and Exhaust Systems

  • Loosen the hose clamp on the turbo inlet and remove the intake pipe from the turbo.
  • Disconnect the charge pipe from the turbo outlet (compressor side). Use a pry bar gently if the O-ring is stuck.
  • Unbolt the downpipe from the turbo exhaust outlet (turbine side). This usually requires removing two or three nuts from the downpipe flange and the V-band clamp.
  • If your vehicle has a secondary air injection system, disconnect the pipe attached to the turbo.

Remove Oil and Coolant Lines

  • Locate the oil feed line from the engine block to the top of the turbo. Use a line wrench to loosen it—hardened heat cycles can make it brittle. Have a catch pan ready.
  • Disconnect the oil return line (drain) at the bottom of the turbo. It connects to the oil pan via a flex hose. Remove the retaining clip or bolt and slide the hose off the turbo fitting.
  • Note the routing of the coolant feed and return lines. These are typically banjo fittings. Remove the bolts and set aside the crush washers—they must be replaced on reassembly.

Unbolt the Turbo from the Exhaust Manifold

  • Support the turbo with a jack or a helper.
  • Remove the nuts securing the turbo to the exhaust manifold (usually four M8 or M10 nuts). Access can be tight; use a swivel socket.
  • Carefully lift the turbo out of the engine bay. Watch for the heat shield, which may need to be removed separately. Inspect the manifold sealing surface; clean off any gasket residue.

Step 2: Preparing the HPA 58mm Turbo for Installation

Before bolting in the new turbo, perform the following pre-installation steps:

  • Prime the oil feed hole: Pour a small amount of clean engine oil into the oil feed port on the turbo cartridge and rotate the turbine wheel by hand. This ensures immediate lubrication on first startup.
  • Check actuator preload: The HPA 58mm turbo may come with an adjustable wastegate actuator. Verify the rod length is set according to HPA’s instructions (typically measured from the actuator arm to the clevis pin). An incorrect preload can cause boost control issues.
  • Install new gaskets: Place the new manifold gasket onto the exhaust manifold studs. Use a thin film of anti-seize on the stud threads.
  • Attach oil and coolant lines to the turbo: Some prefer to loosely connect the oil feed and return lines before mounting, others after. Either way, ensure the O-rings and crush washers are new.

Step 3: Installing the HPA 58mm Turbo

With the new turbo prepped, it’s time to install it.

Mount the Turbo

  • Lift the HPA 58mm turbo into position, aligning the inlet flange with the exhaust manifold studs.
  • Thread the nuts onto the studs by hand. Tighten in a crisscross pattern to the manufacturer’s torque specification (typically 20-24 Nm / 15-18 lb-ft for M8 studs). Use a drop of thread locker on each nut.
  • Reconnect the coolant lines. Tighten banjo bolts to 14-16 Nm (10-12 lb-ft). Replace crush washers each time.
  • Connect the oil supply line. Use a line wrench to tighten to 20 Nm (15 lb-ft). Do not overtighten—damage to the copper or steel line can cause leaks.
  • Slide the oil return hose onto the turbo drain fitting and secure with the clamp.

Reattach Intake, Exhaust, and Charge Pipes

  • Install the discharge pipe from the turbo to the intercooler (charge pipe). Use a new O-ring if necessary. Tighten the clamp to 4 Nm (35 in-lb) approximately.
  • Attach the downpipe to the turbine outlet. Use new flange gaskets and apply anti-seize to the studs. Torque to 25 Nm (18 lb-ft).
  • Reconnect the intake duct to the turbo inlet. Ensure the accordion tube is not kinked.
  • If removed, reinstall the intake manifold with a new gasket. Torque to 10 Nm (7 lb-ft). Do not over-tighten plastic manifolds.

Step 4: Finalizing the Installation – Fluids, Bleeding, and Checks

Refill Oil and Coolant

  • Fill the engine with the specified amount of fresh synthetic oil. Do not overfill; check the dipstick after the first startup.
  • Fill the cooling system with the correct coolant mixture. Use a vacuum filler tool if available to minimize air pockets.
  • Bleed the cooling system per BMW procedure: run the engine with the heater on high, open the bleed screw, and add coolant until no bubbles appear.

System Check and First Start

  • Reconnect the battery. Check all wiring, hoses, and clamps for security.
  • Disable the ignition system temporarily (pull fuel pump fuse or injector connectors) and crank the engine for 10-15 seconds to build oil pressure before first start. This primes the turbo bearing.
  • Re-enable the ignition and start the engine. Let it idle and check for oil and coolant leaks. Listen for any unusual noises from the turbo.
  • Allow the engine to reach operating temperature. Perform a boost leak test (pressurize the intake system to 20psi) to ensure all connections are sealed.

Step 5: Tuning and Proper ECU Calibration

A custom tune is mandatory when upgrading to an HPA 58mm turbo. The stock DME cannot compensate for the increased airflow. Use a flash tuning tool like MHD Flasher, Bootmod3, or a bench flash from a reputable tuner. The tuner will adjust boost targets, fuel timing, ignition timing, and torque limits. Without proper calibration, you risk detonation, overheating, or damage to the engine. Expect to upgrade the fuel system (high-pressure fuel pump, injectors) if aiming for over 500 wheel horsepower.

Essential Tips for a Successful Installation

  • Clean all sealing surfaces thoroughly. Use a plastic scraper to avoid gouging aluminum.
  • Replace the turbo oil return line. The stock line can become brittle and may crack during removal. HPA often provides an upgraded braided line.
  • Check wastegate alignment. After installation, ensure the wastegate arm swings freely and the actuator can close the gate completely. A preload of 3-5mm is typical.
  • Use new bolts for the manifold. BMW recommends single-use stretch bolts for the exhaust manifold. Even if reusing, apply thread locker and torque to spec.
  • Inspect the charge pipe. The stock plastic charge pipe may split under higher boost. Upgrade to a metal charge pipe if you haven’t already.
  • Log your first few pulls. Use a logging tool to monitor boost, lambda, ignition corrections, and intake temperatures to ensure everything is within safe limits.

Frequently Asked Concerns

Will the HPA 58mm turbo require E85 or race fuel?

It can run on 93 octane pump gas with conservative tuning, but to maximize power and safety, an ethanol blend (E30-E50) is strongly recommended. The extra knock resistance allows higher boost and advanced timing.

The HPA turbo typically replaces the stock catalyst location. Depending on your region, you may need a high-flow catalytic converter or a downpipe that moves the cat further downstream. Check local regulations before proceeding.

Conclusion

Installing an HPA 58mm turbo on your N55 is a rewarding project that dramatically transforms the driving experience. The key to success lies in careful preparation, attention to torque specs, and a quality tune. Take the time to double-check every connection and fluid level. If you encounter difficulties, forums like N54Tech offer a wealth of community knowledge, and HPA’s own support team is a valuable resource. With the right approach, you’ll be piloting a much faster, more responsive N55—reliable power that puts a wide smile on your face every time you hit the boost. For further reading, consider the official HPA Motorsport product pages and tuning guides from Bootmod3 or MHD Flasher.