i-vtec aka intelligent vtec relies on a computer to decide when to engage vtec, while the regular vtec has a preset rpm engagement point. Also its believed that i-vtec provides better fuel economy and low end power.it continuously varies the cam angle(to maximize overlap as much as 50° out from the crank timing) as well as second rocker engagement to suit the needs of it's current situation. Also i-vtec doesn't just rely on oil pressure to open an actuator.
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