How are the valves opening and closing time controlled? Chevy Silverado 1500, 2010, 5.3L v8

 

https://en.wikipedia.org/wiki/Variab...kground_theory

The dirt-bike power valve, were just coming out on the bikes, just before I quit racing. They made a big differance in HP, particularly on the 250 cc. They only operated on the .exhaust system, right before the exhuast pipe.attached to the enginre..