BMW 135i/235i/335i N55 Engine
R85,000.00
The BMW N55 is a 3.0-litre, turbocharged, inline 6-cylinder petrol engine produced between 2009 and 2017. It was introduced to replace the highly tunable but maintenance-heavy twin-turbo N54 engine.
As the powertrain for performance-focused models like the BMW 135i (E82/F20), M235i (F22), and 335i (E90/F30), the N55 is celebrated as one of BMW’s most refined straight-sixes. It successfully balanced the brand’s signature linear power delivery with massive mid-range torque, a throatier exhaust note, and significantly improved factory reliability over its predecessor.
Core Engineering Design
The N55 shifted away from the true twin-turbo configuration of the N47/N54 eras, embracing single-turbo efficiency and highly advanced valvetrain control.
- TwinPower Turbo (Single Twin-Scroll): The defining feature of the N55 is its single BorgWarner twin-scroll turbocharger. Instead of using two separate turbos, it features a single turbo housing with two separate exhaust gas inlets. This layout pairs cylinders 1–3 and 4–6 into separate exhaust paths, utilizing pulsing exhaust streams to spool the turbo near-instantly and effectively eliminating turbo lag.
- Valvetronic III integration: Unlike the N54, the N55 incorporates BMW’s Valvetronic variable valve lift system directly alongside Dual VANOS variable valve timing. By using an electric motor to continuously adjust how far the intake valves open, the engine completely bypasses the throttle body during standard driving, sharpening throttle response and dropping fuel consumption.
- All-Aluminium Block with Cast-Iron Sleeves: The open-deck engine block is cast from lightweight aluminium to optimize front-to-rear chassis weight distribution. The cylinder bores are lined with high-strength cast-iron sleeves to handle increased boost pressures.
- Pneumatic vs. Electronic Wastegate (PWG vs. EWG): This is a critical distinction for enthusiasts. Early N55 units (2009 to mid-2013) utilized a vacuum-actuated Pneumatic Wastegate (PWG). From late 2013 onwards, BMW upgraded the engine to an Electronic Wastegate (EWG), which features a larger turbo exhaust outlet and precise electric boost control. This update yields significantly higher tuning potential and stable boost targets.
Technical Profiles
| Specification | Metric Value | Imperial / Standard Value |
|---|---|---|
| Engine Code | N55B30M0 / N55B30O0 | N55B30M0 / N55B30O0 |
| Displacement | 2,979 cc | 3.0 Litres |
| Bore x Stroke | 84.0 mm x 89.6 mm | 3.31 in x 3.53 in |
| Compression Ratio | 10.2:1 | 10.2:1 |
| Valvetrain | DOHC, 24 Valves, Valvetronic III, Dual VANOS | DOHC, 24 Valves, Valvetronic, Dual VANOS |
| Fuel System | High-Pressure Bosch Direct Injection | High-Pressure Bosch Direct Injection |
| Aspiration | Single Twin-Scroll Turbocharger & Intercooled | Single Twin-Scroll Turbocharger & Intercooled |
Performance Output & Applications
The N55 engine was scaled across different models using unique factory software and hardware adjustments (such as high-flow fuel pumps and structural oil pans):
- Standard Output Variant (e.g., E90/F30 335i, E82 135i):
- Power: 225 kW (302 hp / 306 PS) at 5,800 RPM.
- Torque: 400 Nm available exceptionally low down from 1,200 to 5,000 RPM.
- M-Performance Variant (e.g., F20 M135i, F22 M235i):
- Power: Upgraded to 235 kW to 240 kW (315 hp to 322 hp) through optimized scaling, factory overboost maps, and EWG integration.
- Torque: Bumps up to 450 Nm for an aggressive, wider power band.
- (Note: A highly modified version of this architecture with a forged crankshaft was also used to power the early F87 M2, pushing 272 kW / 365 hp).
Critical Maintenance & Failure Points
While the N55 corrected the high-pressure fuel pump (HPFP) and fuel injector failures that plagued the older N54, it introduces its own set of critical maintenance liabilities as it ages:
- Valvetronic Motor and Eccentric Shaft Wear: The electric Valvetronic actuator motor is mounted centrally inside the valve cover and is exposed to high oil temperatures. If oil changes are skipped, the motor gears can wear down or short out. This wear can score the teeth of the expensive internal eccentric shaft, resulting in a sudden engine limp mode and distinct clicking noises when unlocking the car.
- Rod Bearing Failure (Oil Starvation): The N55 bottom end is highly sensitive to oil pressure drops. When performing oil filter housing gasket repairs, any debris or air pockets left in the oil passage can cause localized oil starvation. Under heavy cornering or track use, standard oil pans can allow oil to slosh away from the pickup tube, leading to spun rod bearings and catastrophic internal knock.
- The “Oil Leak Trifecta”: Like most straight-six BMW engines, the N55 suffers from inevitable leaks in three main areas:
- Oil Filter Housing Gasket (OFHG): Leaks oil down the front of the block onto the serpentine belt. If the belt slips off, it can wrap around the crank pulley and be sucked through the front main seal directly into the engine, destroying it.
- Plastic Valve Cover & Gasket: The plastic cover warps and hairline cracks over time, seeping oil onto the hot exhaust shields and filling the cabin with a burning oil odor.
- Oil Pan Gasket: A labor-intensive repair requiring the front subframe to be dropped as the rubber seal degrades.
- Brittle Plastic Chargepipe: The factory intake pipe leading from the intercooler to the throttle body is made of thin, brittle plastic. Even at stock boost levels, the pipe is prone to splitting or blowing completely apart under acceleration, causing an immediate boost leak and drivetrain malfunction error. Upgrading to an aluminium aftermarket chargepipe is considered a mandatory preventative fix.