An internal combustion engine with a plurality of cylinders operating in a four-stroke mode, with pistons moving with reciprocating motion, employs at least one holding tank that is formed within a branch of an intake manifold. The holding tank may be shared among a plurality of cylinders. The holding tank, in response to an opening and a closure of a holding valve within the manifold, serves alternately as a conduit and a tank to convey a pre-combustion gas (fuel-air mix in gasoline engines) to and from the cylinders. Intake valves are held open beyond termination of induction strokes for entry and extraction a quantity of pre-combustion gas from a cylinder to reduce the compression ratio to a value less than the expansion ratio.