System Description: VTEC/VTC

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

Fig 1: VTEC/VTC Driving Condition Graph

Courtesy of AMERICAN HONDA MOTOR CO., INC.

DRIVING CONDITION CHART

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 pumping loss, the intake valve is closed quickly. This gives the air/fuel mixture a charging effect that helps to maximize engine power.