VTEC, My friend told me what it does but...

[JDMFantasy2k]

vtec stands for - Variable valve Timing and Electronic lift Control, Basically, on the camshaft (or shafts in dohc vtec) there is an extra cam lobe. On low rpms the the lobe is disengaged, however when the engine reaches a certain rpm, the extra lobe is engaged and changes the timing of the valves to produce power more efficiently at high rpm's. There's also different types of vtec ( sohc vtec, dohc vtec, i-vtec, e-vtec and i think there's others) it's all basically the same idea but for different purposes (dohc vtec=high performance, e-vtec=engine economy etc) i think that's basically it.