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Varying valve timing yields improvements in emissions, increases fuel economy and gains in power.
Here you can see the valve train - with the VVT actuator being the larger gear connected to the intake camshaft:
Here's a look underneath the engine head at the valves:
The VVT actuator is the heart of the system, using oil pressure built up inside chambers to rotate the output shaft relative to the input shaft, changing the phase angle:
See the small holes where oil travels into the chambers:
This is the solenoid the controls oil flow through the camshaft to actuate the timing gear in advance or retard: