Comment by LeonM

Swedish hypercar builder Koenigsegg has made a system like this, they call it FreeValve.

Their upcoming car called the Gemera will feature FreeValve, its 2.0L 4-cylinder is said to generate over 600HP. Though it must be said that this is a 1.5 million dollar car, so don't expect this kind of performance per displacement from other brands.

A guy on Youtube made his own version of freevalve, and got it to work on a Mazda Miata: https://www.youtube.com/watch?v=E9KJ_f7REGw