Civicvtec.org

What is VTEC?

VTEC is really quite simple. At each cylinder, Honda equips both camshafts with three cam lobes and three rocker arms instead of the conventional two. During low to mid rpm, the two outer cam lobes - which are calibrated for short duration and low lift* - drive the valves via the two outer rocker arms. This setting assures ideal intake and exhaust efficiency at low to mid rpm, resulting in smooth idling, maximum torque and strong horsepower.
When the engine reaches high rpm, built-in hydraulic pins lock the three rocker arms together. And the center cam lobe - which is calibrated for long duration and high lift - drives the valves via the three combined rocker arms. This increases intake and exhaust efficiency at high rpm, resulting in maximum output.
When engine speed is reduced, the hydraulic pins unlock the rocker arms and the two outer cam lobes resume the job of operating the valves.

Switching between the two settings is controlled by a 16-bit Electronic Control Unit, which selects the optimum moment by constantly monitoring engine revolutions, water temperature, load and vehicle speed. Thanks to this simple, thoroughly reliable, award-winning design, the high-rpm output of exotic sports cars and the low to mid range performance of passenger cars can finally be combined in one engine for exciting performance at all rpm.
The pinacle of VTEC implementation is the DOHC VTEC engine. The first engine to benefit from VTEC is the legendary B16A, a 1595cc inline-4 16Valve DOHC engine with VTEC
producing 160ps and first appearing in 1989 in the JDM Honda Integra XSi and RSi.