Differences Between VTEC and i-VTEC

VTEC is a timing system designed by Honda Motor Corporation, which is used on a variety of Toyota, Honda and Acura models like the Honda civic or accord, or the Acura MDX 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 internal combustion 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. Honda sometimes uses the term DOHC in its i-VTEC systems to differentiate different types as well.

How VTEC works

The hallmark of the Honda VTEC-e system is the ability to vary valve timing at both high RPM and low RPM, which is when the exhaust valves close and open within the engine head to improve fuel economy. By altering the lift and duration of valve operation, the engine can optimize both low- and high-performance operation. Prior to VTEC engine designers had to pick where in the RPMrange the engine would be optimized for emissions and performance.

VTEC engines posses a threshold (typically 4500 rpm) above which the VTEC system engages a third rocker arm, which holds the valve open for longer periods, improving high end power. The system was implemented in non-VTEC single overhead engines (SOHC). The VTC (variable timing control) is attached to the end of the camshaft and helps to control valve overlap with the valvetrain.

i-VTEC 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 oil pressure 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, increasing engine speed while providing better engine operation at low and partial throttle. This also results in better fuel economy and less fuel consumption when the car is not operating in turbo mode or at a higher RPM.

Engine Improvements and Specific i-VTEC Profiles

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.

AVTEC

Honda's continual effort to improve the basic VTEC technology continues with the AVTEC (Advanced Variable Valve Timing and Life Electronic Control) system first announced in 2006. While Honda cars have 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, lightening the engine load especially at lower RPM and low speeds.