Manufacturers like to use a lot of acronyms on their cars. Variable valve lift (VVL) and variable valve timing (VVT) are two of the most popular ones. These systems sound pretty similar, but what do they actually do? Luckily, there's a real engineer here to explain it to us.
Variable valve lift is mainly used to enhance performance. Instead of having one cam profile for the entire rev range, a VVL engine has two: low-lift and high-lift. Under regular conditions, the engine will use the low-lift cam to operate the valves, but under higher load, a solenoid switches the engine over to the to the high-lift cam (or cams), increasing valve travel and therefore, performance.
Variable valve timing, on the other hand, is used mainly for emissions control. Essentially, it allows the engine to advance or retard the valve timing using oil pressure. This allows for more control over how much air-fuel mixture is in the cylinder (less under light-load driving, more when power is needed), controlling temperature and emissions.
But that's only a very basic explanation. Watch as Jason Fenske of walks us through VVL and VVT in much more interesting detail.