Engine System Overview

The following provides an overview of the features of the N55 engine:

Crankcase: 

• Large longitudinal ventilation holes inter-connect the crankcase lower chambers and relieve unwanted crankcase pressure between cylinders.
• Modified oil galleries enhance the supply of oil to vacuum pump.

Crankshaft:  Is light weight design and has an asymmetric counterweight arrangement.

Pistons and connecting rods: 

• A specially formed bushing/bore in small end of the connecting rods evenly distributes the force of the pistons on the power stroke.
• Lead-free bearing shells are installed on the big-end of the connecting rods.

Cylinder head: 

• Specially designed water passages intergraded into the cylinder head enhance injector cooling.
• The combustion chambers are machined to work in conjunction with the Valvetronic III system with regard to promoting air turbulence and mixture formation.

Crankcase ventilation: 

• In contrast to the N54, the N55 crankcase ventilation does not use cyclone separators.
• The cylinder and head cover have integrated blow-by passages that connect the crankcase ventilation directly to the intake ports.

VANOS: 

• The N55 VANOS oil passages are simplified compared to the N54 engine.
• The solenoid valves have integrated non-return valve and 3 screen filters.
• The VANOS units are of a lightweight design for increased adjustment speed and have a reduced susceptibility to soiling.

Valvetrain: 

• The N55 is the first BMW turbo engine to incorporate Valvetronic.
• The valvetrain is a new designed that combines Valvetronic III with Double VANOS.
• With Valvetronic III the 3rd generation brushless servomotor is introduced.
• The position detection sensor of eccentric shaft is now integrated in the servomotor.

Oil supply: 

• An enhanced and simplified oil circuit design is used.
• The inlet pipe, oil deflector, and oil collector are combined in one component.
• Oil pump uses a Duroplast slide valve and it is electronically controlled based on a characteristic map within the engine management.

Forced induction: 

• The N55 uses a single twin scroll turbocharger with vacuum operated, electronically controlled wastegate valve.
• The electric diverter valve is intergraded into the turbocharger compressor housing.

Air intake and exhaust system: 

• Air intake system is similar in configuration as the N54 with the exception of the intake manifold and the use of a single turbo.
• The intercooler is an air to air type mounted in the lower area of the front bumper cover.
• The exhaust system uses no underbody catalytic converter.

Vacuum system: 

• The N55 engine has a two-stage vacuum pump as on the N54.
• The vacuum system has the vacuum reservoir built into the cylinder head cover.

Fuel injection: 

• HDE (high pressure fuel injection) system is installed on the N55.
• The HDE system uses solenoid valve fuel injectors instead of the piezoelectric type used on HPI.
• The high pressure pump and pressure sensors are similar in design and function in both the HDE and HPI systems.

Digital Motor Electronics (DME): 

• The DME is mounted on the intake manifold and cooled by intake air.
• The location of the DME facilitates the installation of the N55 engine in several current BMW platforms/models.