BMW S55 Engine — The M3/M4 Powerplant Explained

Overview

The S55 is BMW M's 3.0-liter twin-turbocharged inline-six, powering the F80 M3 and F82/F83 M4 from 2014 to 2018. It's based on the N55 architecture but extensively reworked by BMW M with twin turbos, forged internals, and a higher-revving design.

Key Specifications:

• Displacement: 2,979 cc
• Bore x Stroke: 84.0 mm × 89.6 mm
• Compression Ratio: 10.2:1
• Max Power: 431 hp (317 kW) @ 5,500-7,300 rpm (standard), 450 hp (Competition)
• Max Torque: 550 Nm (406 lb-ft) @ 1,850-5,500 rpm
• Turbochargers: Twin Mitsubishi TD04-19T
• Engine Management: Bosch MEVD17.2.9

M Division Upgrades over N55

• Forged crankshaft (N55 uses cast)
• Forged connecting rods
• Reinforced pistons with oil squirters
• Twin turbochargers instead of single twin-scroll
• Oil-to-water intercooler (air-to-liquid)
• Dedicated oil cooler with thermostat
• Higher flow exhaust manifold

Known Issues

1. Crank Hub Failure

• The most critical S55 issue. The crank hub (front pulley) can spin on the crankshaft nose, destroying timing and potentially the engine.
• Cause: Insufficient press-fit from factory. Aggressive driving and high torque loads worsen it.
• Solution: Preventive crank hub fix — pinning or keying the crank hub. This is considered MANDATORY for any tuned S55.

2. Charge Pipe / Boost Pipe Failure

• Frequency: Very common, especially on tuned cars
• Solution: Aftermarket aluminum charge pipes

3. Oil Consumption

• Frequency: Moderate — some S55s consume 1L per 3,000-5,000 km
• Cause: Piston ring design, high-RPM operation
• Solution: Monitor oil level. Some owners switch to thicker oil (0W-40).

Tuning

Stage	Power	Torque	Notes
Stock	431/450 hp	550 Nm	Standard/Competition
Stage 1	520-550 hp	680-720 Nm	ECU tune, crank hub fix mandatory
Stage 2	580-620 hp	750-800 Nm	Downpipes + tune
Stage 2+	650-700 hp	850+ Nm	Full bolt-ons + E85

Critical: Always do the crank hub fix before any tuning. This is non-negotiable.

The S55 is a phenomenal engine that combines M car character with modern turbo performance — just respect the crank hub.