An Elevated Expansion-Ratio Internal Combustion Engine has a substantially standard repeating four-stroke sequence for each of a plurality of cylinders. The head of each cylinder has an intake valve, a combustion-gas exhaust valve, and a vapor return valve. A return manifold for vapor connects from respective ones of the cylinders via a plurality of valve assemblies, each of which includes the return valve, into a passage ahead of a beginning portion of an intake manifold. Each valve assembly also has a discharge valve coupled to the return valve via a holding tank for cylinder vapor or gas. Valve stems of the discharge and return valves are coaxial in a single section valve housing or spaced-apart in a two-section valve housing. A quantity of the vapor is received into the holding tank during the compression stroke, and subsequently transferred via the discharge valve to the return manifold.