VTEC is a timing system designed by Honda Motor Corporation, which is used on a variety of Honda and Acura models in every major automotive market. VTEC stands for Variable Valve Timing and Lift Electronic Control. The system was upgraded to i-VTEC in the early 2000s, which added intake camshaft timing adjustment. VTEC implementation differs in different engine families across the Honda and Acura range, thus the i-VTEC implemented in the current R-series Honda engines, for instance, is different than the i-VTEC system equipped on K series engines.
The hallmark of the Honda VTEC system is the ability to vary valve timing, which is when the exhaust valves close and open within the engine head. By altering the lift and duration of valve operation, the engine can optimize both low- and high-end operation. Prior to VTEC engine designers had to pick where in the revolution range the engine would be optimized for performance.
VTEC engines posses a threshold (typically 4500 rpm) above which the VTEC system engages a third rocker arm, which hold valves open for longer periods, improving high end power. The system was implemented in single- and dual-overhead engines.
i-VTEC (intelligent Variable Valve Timing and Lift Electronic Control) was introduced in 2002 to the North American market. The i-VTEC system added additional control for intake valves at low and medium throttle levels, thus improving low-end and partial throttle response from the engine. Thus, the i-VTEC system provides all the benefits of the traditional VTEC design's high-end open throttle power, while providing better engine operation at low and partial throttle.
The i-VTEC system was implemented into more modern K series engine, as opposed to the VTEC system of the older B series engines. There is a performance i-VTEC system, and an economy i-VTEC system. The performance variant allowed three cam lobes per cylinder for both intake and exhaust, whereas the economy i-VTEC system only possesses two lobes on the intake cam, and no VTEC control on the exhaust cam. The performance version resulted in an additional 40 horsepower in the K series engines.
Honda's continual effort to improve the basic VTEC formula continues with the AVTEC (Advanced Variable Valve Timing and Life Electronic Control) system first announced in 2006. While Honda has not met the initial goal of release of AVTEC by 2009, the system continues under development. AVTEC combines continuously variable phase control with the i-VTEC system. Honda estimates the system will result in a 13 percent increase in fuel efficiency.
