I was thinking about the valving system in a regular IC engine. The valves have huge springs on them and require a lot of force to open. The camshaft/lifter system makes for a lot of drag and lost horsepower. Instead of making the valves move up and down, why not make them spin? Imagine a a salt shaker with a turning lid. The lid turned to one side exposes holes for the salt to fall through, and turned to the other side closes the holes. I guess it's the same idea as a rotary valve. Why can't valves be shaped like half circles and have them spin open at the right time. It seems more efficient, but I can't really see any of the problems that would occur. Any thoughts?