Vacuum System
The vacuum system is similar to that of the N63 engine. A two-stage vacuum pump is used, the main stage of which generates the vacuum for the brake servo. The auxiliary stage generates the vacuum to activate the wastegate valves of the exhaust turbochargers and the exhaust flaps.
N74 Vacuum System
INDEX EXPLANATION REFERENCE CHART
| Index | Explanation |
|---|---|
| 1 | Vacuum pump |
| 2 | Non-return valve for auxiliary vacuum units |
| 3 | Non-return valve for brake servo |
| 4 | Non-return valve on brake servo |
| 5 | Brake servo |
| 6 | Electric changeover valve |
| 7 | Vacuum unit for exhaust flaps |
| 8 | Vacuum accumulator |
| 9 | Vacuum solenoid (EPDW) |
| 10 | Vacuum unit for wastegate valve, cylinder bank 1 |
| 11 | Vacuum accumulator |
| 12 | Vacuum solenoid (EPDW) |
| 13 | Vacuum unit for wastegate valve, cylinder bank 2 |
In contrast to the N63 engine, the N74 engine has two vacuum reservoirs for the wastegate valves. These are attached to the rear end of the intake system. Vacuum solenoids (EPDW) for the wastegate valves are mounted directly on the vacuum reservoirs (see arrows).