Variable Valve Timing
Benefits: Fuel economy, more flexible power delivery
Drawbacks: Greater cost to produce
If you're at all familiar with Honda engines, you've almost certainly heard the term VTEC. People who tune their Hondas for performance often speak of "VTEC kicking in." But what exactly does that mean?
VTEC refers to variable valve timing and lift electronic control, a form of variable valve timing. There are times when an engine requires more air flow, like during hard acceleration, but a traditional engine often does not allow enough air to flow, resulting in lower performance. Variable valve timing means the flow of air in and out of the valves is slowed down or sped up as needed [source: Autropolis].
Honda is hardly the only car company to offer such a system. Toyota has one they call VVT-i, for variable valve timing with intelligence, and BMW has a system called Valvetronic or VANOS, which stands for variable Nockenwellensteuerung, meaning variable camshaft control. While they all work a little differently, they all accomplish the same task -- allowing more air and fuel into the valves at different speeds. This makes an engine more flexible and allows it to deliver peak performance in a variety of conditions. It also increases fuel economy.
Many engines now incorporate some form of variable valve timing, often controlled by the engine's on-board computer. We'll talk about how engine computers have revolutionized design in this next section.