An internal combustion engine, having a cylinder with a translating piston therein, employs a holding tank connecting, via a valve, to the combustion chamber of the cylinder for receipt of a portion of the engine gasses expelled during a compression stroke for providing that the expansion ratio of an expansion stroke is greater than the compression ratio of the compression stroke. The holding tank is located within a head of the cylinder, and has a single port serving for both ingress and egress of gasses to the combustion chamber. The holding tank is provided with one or more additional passages for connection to one or more additional cylinders in the event that the holding tank is shared among two or more cylinders.