System Description: VTEC/VTC: Notes

The i-VTEC has a variable valve timing control (VTC) mechanism on the intake camshaft in addition to the usual VTEC. This mechanism improves fuel efficiency and reduces exhaust emissions at all levels of engine speed, vehicle speed, and engine load.
The VTEC mechanism changes the valve lift and timing by using more than one cam profile.
The VTC changes the phase of the intake camshaft via oil pressure. It changes the intake valve timing continuously.

Fig 1: Graph For VTEC/VTC With Different Driving Conditions
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Driving Condition	VTC Control	Description
(1) Light-load	Base Position	For stable combustion, the cam angle is retarded and reduces the entry of exhaust gas into the cylinder.
(2) Medium/high-load	Advance Control	Cam phase angle is controlled to optimize valve timing, improving fuel efficiency and reducing emissions.
(3) High speed	Advance-Base Position	To reduce the pumping loss, the intake valve is closed quickly. This helps the entry of fuel air mixture by the charging effect, and maximizes engine power.