Hello Scotty, I've enjoyed your shows and experience for years.  There is an engine we're working on that's a different twist on efficiency.  It involves delaying closing the intake valve during compression to actually push air back out.  We're designing an engine that will achieve a pressure no greater than 11 bar at TDC yet it will expand 30 times during the power stroke from its original volume.  Fuel will be introduced  through direct injection.  You can quickly observe this eliminates NOX, knock, detonation, and rough idle.  We're striving for a specific fuel consumption of .25 ibs of gasoline per horsepower per hour.(American measurements) for the folks interested.  There are also some other interesting thermal efficiency increases available through using an almost diamond hard cylinder liner that also is a very poor conductor of heat.  The piston crown is to be insulated with a ceramic along with the head and valves.  The bore and stroke on the experimental engine will be 3.8"×3.8" because as you know, the physically larger a cylinder is, the more thermally efficient it becomes due to reduced squelch verses the displacement.  We should be able to meet the efficiency of a ship diesel made by Wartsila Sulzer in an engine a tiny fraction the size with very little mechanical complication other than the intake valve delaying cam lobes.  Drop me a line for more information and no, I'm not selling a darn thing, just letting you know a different possibility on the "variable compression" twist without the complexity of the Nissan design.