I am trying to understand how effectively reducing the compression ratio of the combustion chamber, you are "increasing efficiency?"
In a conventional engine design, increasing static compression ratio will increase the energy gained...up to the maximum point the fuel you are using will handle..
Perhaps just do what all modern car manufacturers try to achieve..control the flamefront / swirl through the engine with head / piston design, and try to reduce the ignition / expansion of gasses event to be as close to TDC as possible (To prevent the expansion of gasses pushing the piston backwards on its upstroke).
- Improve head desgin to promote better combustion
- Improve piston design to promote better combustion
- Reduce time before TDC
- reduce friction in the combustion chamber (Short skirts, lighter weight)
- Use higher quality materials that do not transfer heat (Ceramics etc)
- use higher quality fuel that allows quicker, more controlled flamefronts
Of course, a standard internal combustion engine (4 stroke especially) is pretty poorly designed interms of efficiency..
Maybe look at the Miller Cycle / Wankel / etc engine designs..many are much more efficient than a typical 4 stroke..of course they have a few other faults that need to be taken into account..(Reliability / emissions / size / weight / serviceability etc)