by 
The Curious Bag
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The difference between VTEC engines and non-VTEC engines is that one has a VTEC system and the other does not. This cam-phasing system has become endemic to today's marketplace, but only one manufacturer can claim to have been there first.
History
Honda originally introduced this system on its flagship NSX, which proved so successful that nearly every manufacturer has since adopted some variant of the system.
Purpose
An engine's air intake (and thus power potential) is determined by the camshaft, which dictates how far the valves open and how long they remain open.
Advantages
Though big cams allow the engine to breathe better, they cause rough idling and poor fuel economy. VTEC systems allow Honda engines to phase back and forth between a big, high-rpm cam for top end power and a smaller one for better emissions, smoother idle and better fuel economy.
Function
VTEC engines use an electrically activated solenoid to engage the larger cam at high rpm, reasoning that if the driver is revving the engine past 5000 rpm, he is not interested in fuel economy.
Equivalents
Many manufacturers have adopted a system based on Honda's VTEC. Toyota calls its VVTL-i, Mitsubishi has MIVEC and GM uses a slightly less sophisticated version designated VVT.
Source:
Resource:
VTEC Animation (Video)
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