Impreza WRX Wagon F4-2.0L DOHC Turbo (2002)
When the supercharging pressure reaches the predetermined level, the wastegate controller lets the supercharging pressure press the diaphragm.
This causes the wastegate valve to open through a linkage. With the wastegate valve open, part of the exhaust gas is allowed to flow into the
exhaust gas pipe that bypasses the passage to the turbine.
This decreases the exhaust gas pressure that rotates the turbine and keeps the supercharging pressure constant.
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It means P2 - P1 = constant.
P1: Atmospheric pressure
P2: Supercharging pressure
2. CONCEPT OF THE WASTEGATE VALVE CONTROL
At high altitudes, the atmospheric pressure (P1) is low, so that the supercharging pressure (P2) is also low in a conventional system. The wastegate
solenoid valve operates in such a way that a constant supercharging pressure (P2) is maintained by acting in response to change in the atmospheric
pressure.