Impreza WRX F4-2.0L DOHC Turbo (2004)
Variable Induction Control Valve: Description and Operation
TUMBLE GENERATOR VALVE
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A tumble generator valve is provided on each engine bank, between the intake manifold and intake air ports. The right bank tumble generator
valve has butterfly valves for the #1 and #3 cylinders and the left bank tumble generator valve has those for the #2 and #4 cylinders. The two
butterfly valves in each tumble generator valve are fitted on a single shaft that is driven by an actuator.
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The tumble generator valves are controlled by the ECM according to the coolant temperature and the time elapsed after start of the engine. When
the engine is started, the butterfly valves are moved to the closing ends. In this state, the intake air flows at very high speeds passing through
narrowed passages in the directions determined by the individual intake air ports in the cylinder head. This creates tumbling air motions in the
cylinders, which enables lean mixtures to be ignited and thus harmful exhaust emissions to be reduced during engine start. The tumble generator
valves are fully open when the engine is operating at an ordinary driving speed, allowing intake air to flow without being changed in direction and
velocity.
