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: Engine Load And Engine Speed Diagram

Courtesy of AMERICAN HONDA MOTOR CO., INC.