V-TEC or Variable Valve Timing and Electronic Lift Control, is more than just a power producing tool.It changes the lift, and cam timing to accomodate to different driving styles.If you are just doing regular daily driving the cam timing gets retarded and the valves dont lift as high, which gives you a much high MPG rate.Once you hit the V-TEC engagement point (Around 6000RPMs depending on engine model) the ECU senses this and begins to advance the timing and lift the valves more to allow the engine to run strong but less efficiently.So, technically, V-TEC is always engaged, it is just engaged for different purposes. Allowing you to get high MPG and still be able to achieve spirited driving from time to time.