Air Intake and Exhaust System: Turbocharger: Notes

The N55 is equipped with a single twin scroll turbocharger instead of two separate small turbochargers as on the N54 engine. The following graphics shows the operating principle of the twin scroll turbocharger.

Fig 1: Identifying Twin Scroll Turbocharger Components Rear View

Courtesy of BMW OF NORTH AMERICA, INC.

INDEX EXPLANATION CHART

Index	Explanation
A	Exhaust duct 1 (cylinders 1 - 3)
B	Exhaust duct 2 (cylinders 4 - 6)
C	Connection to catalytic converter
D	Inlet from intake silencer
E	Ring channel
F	Outlet to intercooler
1	Wastegate valve
2	Lever arm, wastegate valve
3	Vacuum unit for wastegate valve
4	Diverter valve
6	Turbine wheel
8	Cooling duct
10	Oil return
11	Coolant return

Fig 2: Identifying Twin Scroll Turbocharger Components Front View

Courtesy of BMW OF NORTH AMERICA, INC.

INDEX EXPLANATION CHART

Index	Explanation
A	Exhaust duct 1 (cylinders 1 - 3)
B	Exhaust duct 2 (cylinders 4 - 6)
C	Connection to catalytic converter
D	Inlet from intake silencer
E	Ring channel
F	Outlet to intercooler
1	Wastegate valve
2	Lever arm, wastegate valve
3	Vacuum unit for wastegate valve
4	Diverter valve
10	Oil return
11	Coolant return

Fig 3: Identifying Twin Scroll Turbocharger Components

Courtesy of BMW OF NORTH AMERICA, INC.

INDEX EXPLANATION CHART

Index	Explanation
A	Exhaust duct 1 (cylinders 1 - 3)
B	Exhaust duct 2 (cylinders 4 - 6)
C	Connection to catalytic converter
D	Inlet from intake silencer
E	Ring channel
F	Outlet to intercooler
1	Wastegate valve
2	Lever arm, wastegate valve
3	Vacuum unit for wastegate valve
4	Diverter valve
5	By-pass
6	Turbine wheel
7	Compressor wheel
8	Cooling duct
9	Turbine shaft