[Diesel_Dave]

Late and/or early intake valve closure has been used before for efficiency improvement. It's typically called Miller cycling or Atkitson cycling (depending on who you ask). The Toyota Prius engine uses this. The effect is an expansion ratio which is greater than the compression ratio. What you're suggesting wouldn't change the effective compression ratio and I'm not sure as how it would reduce pumping losses. Remeber that lower cylinder pressure on the intake stroke is going to increase pumping losses.