Introduction: The N55 and the BMS Stage 2 Turbo Upgrade

The BMW N55 engine, introduced in 2010, quickly became a favorite among enthusiasts for its blend of smooth power delivery and single-turbo simplicity. While the stock turbocharger offers respectable performance, many owners eventually seek more without sacrificing daily drivability or long-term reliability. Enter the BMS Stage 2 Turbo from Burger Motorsports—a cost-effective, drop-in upgrade designed to push the N55 well past its factory output limits.

This upgrade isn't just about peak numbers. It's engineered to improve spool characteristics, sustain higher boost levels safely, and maintain the plug-and-play nature that BMS is known for. Whether you're tracking your car, hitting straights, or simply want a more exhilarating daily commute, the Stage 2 turbo is a proven path to serious power. However, success depends on understanding the supporting ecosystem—from proper installation to fuel choice and tuning. This guide covers everything you need to know to make your BMS Stage 2 turbo upgrade a reliable, high-performance success.

Key Benefits of the BMS Stage 2 Turbo

Before diving into installation specifics, it's worth examining exactly what this upgrade brings to the table compared to a stock N55 turbo or even a Stage 1 hybrid.

Significant Power Gains with Strong Mid-Range

The BMS Stage 2 turbo features a larger compressor wheel and revised turbine housing compared to the stock unit. On a properly tuned N55, this translates to peak gains of 80–100 whp and 70–90 wtq over a stock turbo with similar supporting mods. More importantly, the boost threshold is only slightly raised—full spool arrives around 3200–3500 rpm instead of the stock 2800–3000 rpm—but the mid-range torque curve is dramatically fatter, pulling hard well past 6500 rpm.

Improved Throttle Response and Spool Characteristics

Despite a larger compressor, BMS uses a billet wheel with advanced aerodynamics to reduce lag. The result is sharper tip-in response and a more linear delivery of power. This makes the car easier to modulate in corners and during daily merges, unlike larger frame turbos that can feel sluggish before hitting boost.

Reliable Performance with Conservative Boost Levels

Burger Motorsports designed the Stage 2 turbo to run reliably at 18–22 psi on pump gas and up to 24–26 psi with ethanol blends. The upgraded thrust bearing and improved oiling system resist failure common to high-mileage stock turbos. When paired with a proper tune, this turbo often outlasts cheaper alternatives while delivering consistent track-day performance.

Cost-Effective Upgrade Path

At roughly half the price of full-frame turbo kits (like Pure Stage 2 or Vargas), the BMS Stage 2 offers outstanding value. It requires minimal modification to existing piping and fits all N55 models (E90, F30, F22, F87 M2, etc.) without requiring a new manifold or downpipe relocation. This makes it an ideal entry point for enthusiasts stepping up from Stage 1 tunes.

Installation Process: Step-by-Step Guide

Installing the BMS Stage 2 turbo is a medium-difficulty job best tackled over a weekend. Budget for 8–12 hours if you're experienced with N55 work, or 14–18 hours if you're learning. Below is a detailed breakdown.

Required Tools and Parts

  • Socket set (10mm, 13mm, 15mm, E-torx sockets)
  • Torque wrench (in-lb and ft-lb range)
  • Pry bar, pick set, and flathead screwdriver
  • Engine coolant (if removing the coolant pipe), new oil and filter
  • New gaskets: turbo inlet, exhaust manifold, downpipe, O-rings for oil/coolant lines
  • Turbo stud kit (if reusing old ones)
  • Jack stands or lift

Preparation and Removal

  1. Disconnect the battery and let the engine cool completely. Remove the engine cover, intake duct, and air filter box.
  2. Drain engine oil and coolant (if removing the coolant feed line). BMS recommends replacing all fluids during the swap.
  3. Remove the downpipe and oxygen sensors. Unclip the wastegate vacuum line and boost sensor harness.
  4. Unbolt the exhaust manifold from the cylinder head (13mm nuts). Carefully separate the manifold from turbo studs.
  5. Disconnect oil and coolant lines from the turbo. Use a catch pan for residual fluids.
  6. Lift the turbo out of the engine bay from above. On xDrive models, you may need to drop the subframe slightly.

Installing the BMS Stage 2 Turbo

  1. Transfer all reusable brackets and the wastegate actuator from the old turbo. Apply anti-seize to studs.
  2. Install new gaskets on the manifold and turbo oil/coolant ports. BMS supplies updated hardware.
  3. Position the new turbo into the exhaust manifold from above. Align the studs and hand-tighten the manifold nuts.
  4. Reconnect oil and coolant lines. Torque bolts to manufacturer spec (typically 18–22 ft-lb for banjo bolts).
  5. Reinstall the downpipe with a new gasket. Tighten studs evenly.
  6. Bleed the cooling system using BMW's no-spill coolant funnel method.

Post-Installation Checks

Refill oil (use a high-quality 5W-30 or 0W-40), start the engine, and check for leaks. Let it idle for 5 minutes, then perform a short test drive without heavy boost. Log boost pressure and fuel trims to confirm proper operation before any hard pulls.

Reliability Considerations

A BMS Stage 2 turbo, when installed correctly and supported by proper maintenance, is a reliable piece of hardware. But pushing the N55 beyond factory limits introduces new failure points—here’s what to watch.

Oil Supply and Drainage

The N55’s turbocharger relies on consistent oil flow for cooling and lubrication. With the Stage 2 turbo generating more heat, use only OEM or equivalent oil filters and change oil every 3,000–4,000 miles if running high boost or ethanol. Consider an aftermarket oil cooler if tracking the car repeatedly.

Boost Control and Wastegate

The BMS Stage 2 turbo uses an upgraded actuator that holds boost more precisely. However, factory electronic wastegate controllers can struggle with higher spring pressure. Many enthusiasts report improved consistency with an MHD or JB4 custom tune that adjusts wastegate duty cycles. If you see boost oscillation or overboost, recalibrate the wastegate adaptation using a diagnostic tool.

Engine Internals Limits

Stock N55 rods and pistons can handle up to 500–520 whp on a safe tune, which the BMS Stage 2 can approach with ethanol or race gas. To stay on the safe side, limit boost to 22 psi on pump gas and 25 psi on E30. If you plan to exceed those levels, invest in forged internals and a larger fuel pump.

Heat Management

Increased boost raises exhaust gas temperatures (EGT). Install a high-capacity intercooler (like the CSF or VRSF race version) and consider a ceramic coating on the turbo heatshield to reflect radiant heat. Monitoring IATs via a Cobb or MHD logger is essential during summer driving.

Fuel System Requirements

The stock N55 high-pressure fuel pump (HPFP) can sustain up to 22 psi on pump gas, but beyond that, you may need an upgraded HPFP (Spool Street or Visconti). Ethanol mixes (E30–E40) require a fuel pump controller or secondary injection to maintain rail pressure. Always log fuel pressure when pushing past 18 psi.

Performance Tips for Maximum Output

Simply bolting on the BMS Stage 2 turbo without optimizing the rest of the system leaves power on the table. Follow these tips to extract the most from your upgrade.

ECU Tuning: The Crucial Ingredient

A quality tune is mandatory. The BMS Stage 2 turbo works best with a custom or OTS map from MHD, Bootmod3, or Kevin S. at XDI. A Stage 2+ file that targets 20–22 psi on 93 octane is a safe starting point. For ethanol blends, request a custom map with advanced timing and increased fuel scalars. Avoid generic piggyback maps that don’t account for the larger turbo’s flow characteristics.

Upgrade the Charge Pipe and Intercooler

The stock plastic charge pipe tends to crack under higher boost. Replace it with an aluminum or silicone unit (e.g., FTP or VRSF). Pair it with a stepped intercooler that maintains intake air temperatures within 10–15°F of ambient. This alone can prevent knock and allow timing advance.

High-Flow Downpipe and Exhaust

A catted or catless downpipe significantly reduces backpressure, helping the turbo spool quicker. Combine with a 3-inch or 3.5-inch midpipe and free-flowing axle-back (like an AWE or Remus) to drop exhaust temperature by 50-100°F. Just ensure emissions laws allow catless operation in your area.

Intake and Inlet Pipe

Upgrade to a high-flow intake system (e.g., BMS intake or Eventuri) and a larger turbo inlet pipe (4-inch silicone) to reduce restriction before the compressor wheel. This adds 5–8 whp at peak and improves transient response.

Boost Logging and Fine-Tuning

Use a MHD WiFi adapter or JB4 mobile app to log parameters: boost target vs actual, fuel trims, IAT, and knock correction. Adjust wastegate duty cycles or target boost in 0.5 psi increments until you see consistent spool without oscillation. Many tuners offer remote tuning sessions if you provide logs.

Maintenance and Longevity

To keep your BMS Stage 2 turbo running strong for 60,000+ miles, adopt a stricter maintenance routine:

  • Oil changes: Every 3,000 miles with a premium synthetic. Use Liqui Moly 5W-30 or Motul 8100 X-cess.
  • Spark plugs: NGK 2-step colder plugs (97506 gapped to 0.022 in). Replace every 15,000–20,000 miles.
  • Walnut blasting: Every 30,000 miles to prevent carbon buildup on intake valves, which robs flow.
  • Coolant flush: Every 2 years with BMW blue coolant.
  • Boost leak test: Annually using a smoke machine on the charge pipes and intake boots.

If you experience oil consumption above 1 quart per 1,000 miles, check the turbo oil return line and PCV system. A clogged crankcase ventilation can pressurize the turbo seals.

Cost Analysis and Alternatives

The BMS Stage 2 turbo typically retails for $1,200–$1,400 (complete unit with wastegate). Compare this to:

  • Pure Stage 2: ~$2,500 (larger compressor, requires upgraded inlet and tune)
  • Vargas GC Lite: ~$2,000 (ball bearing, faster spool but more expensive)
  • Full frame kits (Precision, Garrett): $4,000+ (require fabrication, not street-friendly)

For the price, the BMS Stage 2 offers the best balance of easy install, daily driveability, and reasonable power ceiling (450–500 whp). If you want 500+ whp reliably, the Pure Stage 2 is a better long-term investment with its dual-ball bearing cartridge.

Conclusion: Is the BMS Stage 2 Turbo Right for You?

Upgrading to the BMS Stage 2 turbo transforms the N55 from a quick daily driver into a serious street machine capable of embarrassing much more expensive cars. The installation is straightforward for a competent DIYer, and the supporting community of BMS, MHD, and Bootmod3 tuners makes dialing in the setup easier than ever.

This upgrade is ideal for the enthusiast who wants a significant power bump without the complexity or cost of a full turbo kit. It’s also a great stepping stone for those planning future engine builds. As long as you respect the need for proper cooling, fuel system upgrades at higher power levels, and diligent maintenance, the BMS Stage 2 turbo will reward you with exhilarating performance mile after mile.

For additional reading, check out the official BMS Stage 2 product page, the detailed installation guide on E90Post forums, and tuning resources from MHD Tuning and ProTuningFreaks.