An Elevated Expansion-Ratio Internal Combustion Engine has a substantially standard repeating four-stroke sequence for each cylinder, and the Engine includes for each cylinder: an intake valve, a combustion-gas exhaust valve, and a vapor return valve. A return manifold for vapor connects from the return valves of respective ones of the cylinders back into a passage ahead of a beginning portion of an intake manifold. Substantially during a predetermined part of each compression stroke in the sequence of strokes, the return valve opens after a closing of the intake valve, and thereafter closes at a time within the compression stroke corresponding to a predetermined position of the piston in the cylinder.