You can maybe try
www.howstuffworks.com . Sometimes they have stuff like this.
I know that some of the diesel manufacturers are experimenting with hydraulically operated valves and one of their objectives is multi-displacement and variable dynamic compression. The "cam" is very much like the fuel pump in a diesel; computer controlled high pressure, but it presses oil into a lifter cavity. The computer controls how and when it sends oil to the lifters thereby creating nearly infinitely adjustable valve lift and timing.
That's the only system I know of right now. I'm sure I read about another one somewhere but its escaping me now.