Variable Timing and Lift Electronic Control, commonly called VTEC, was invented by Honda’s engineer Ikuo Kajitani and was the first system of its kind; it is noticeably different from a standard VVT (Variable Valve Timing by Toyota) which press on the valve timing only and does not alter the camshaft profile or valve lift by any means.
It has two different cam lobes (which are Oval Shaped lobes that are mounted on a Cam Shaft) that open the ingestion Valves (Valves that lets Air & Fuel Mixture flow inside the Cylinder); these lobes are one for each Low and High RPM. Changing through cams is controlled by an ECU and is depends upon: throttle position, engine speed, vehicle speed, engine temperature and engine oil pressure. The timing and duration of opening also differs on the center of Engine’s RPM. Vtec was brought in 1989 as a DOHC (Double Over Head Camshafts) system and in time Honda also developed the I - Vtec and I – Vtec Hybrid versions of the same. With growing reputation and marketing value of the VTEC, Honda has introduced it to SOHC (Single Over Head Camshafts) engines that shares a common camshaft equally for intake and exhaust valves, such an bargain offered the profit of VTEC mechanism to ingestion valves only, merely because VTEC needs an additional 3rd Centre Rocker Arm and cam lobe (one each for ingestion and exhaust side), also the sparks located between two exhaust rocker arms, leaves no room for a VTEC rocker arm. Further, camshaft’s centre lobe can either be used by intake or exhaust, thereby, limiting the benefit trait to one side. Though, Honda is currently using SOHC VTEC Mechanism on both the Intake and the Exhaust valves.