Vtec is honda's patented system for variable Cam Profiles. It effectively gives an engine two independent cam profiles. The idea is that the Low Cam has conditions optimal for low RPMs and the High Cam has conditions optimal for higher RPMs. Vtec motors generally have a broader powerband characterized by two "humps" as opposed to one hump with non-vtec motors. The ideal Vtec Crossover Point can be found by superimposing a dyno graph of the Low Cam and High Cam and seeing where they cross.