VTEC is Variable (Valve) Timing Engine Control. Honda´s VTEC is actuated by oil pressure in the head. That´s why its possible to tap oil in the block and "frankenstein" a Honda motor. <---That´s a pretty good analogy, Blade... too bad my bro´s SI will spank my car
I have to correct something here. VTEC means Variable Valve Timing and Electronic Lift Control. The acronym is way off, i know. my brother owns a Civic SI and i´ve researched his car numerous times. Blade is right about the oil pressure part, though. The pressure locks the secondary cam lobes into the secondary position, there by making them control the valves... which all it really does is open the valves for a split second more, allowing more air to flow into the combustion chamber, creating 160 horsepower, thats also why at 5500 rpm in the 2000 Civic SI, the engine starts to roar REALLY loud... It´s the only thing i like about that car.
Toyota´s VVT-i does basically the same thing, only oil pressure doesn´t change cams, really the cams don´t change over at all. The ECU basically reads the air/fuel mix and constantly retards/advances the timing for better performance/fuel economy at all times. I still want to buy the new 2003 Corolla S, it has a VVT-i engine in it.
I could care less about Chevy´s ECOTEC, because it´s in two of the ugliest cars i´ve ever seen before in my life, the new Cavaliers and the new Sunfires.
I guess, since i can´t find anything directly related to "Zetec" that Zetec is basically two processes used by Ford. 1. VCT or Variable Intake Cam Timing, which is basically the ECU advancing and retarding the time to give more power in all the rpm range. And 2. DSI, Dual-Stage Intake Manifold. This just shortens and lengthens the intake manifold depending on RPM.