A system comprising: a piston arranged to move within a cylinder of an internal combustion engine; a crankshaft connected to the piston by a connecting rod, the crankshaft arranged to rotate under influence of movement of the piston in the cylinder in accordance with an engine speed commanded by a throttle control; a junk head disposed opposite the piston proximate to a first end of the cylinder, the junk head comprising one or more compression or oil-sealing piston rings, the junk head arranged to be at least one of stationary in the cylinder and moveable between at least two positions to vary a distance between the junk head and a top dead center position of the piston at a rate governed by a control; and a first sleeve valve associated with a first port connecting to a combustion chamber defined at least in part by a head of the piston, an internal surface of the junk head, and the first sleeve valve, the first sleeve valve at least partially encircling the piston and arranged to open and close the first port by first movement between a first open position and a first closed position, the first movement comprising the first sleeve valve temporarily ceasing its motion in a direction aligned with an axis of the cylinder at the first closed position and at the first open position; characterized in that the rate at which the distance between the junk head and a top dead center position of the piston is varied is governed by the throttle control rather than by a speed at which the internal combustion engine is operating; and a first sealing edge of the first sleeve valve being urged into contact with a first valve seat at the first closed position such that the first sealing edge is closer to the first end of the cylinder at the first closed position than at the first open position. a piston arranged to move within a cylinder of an internal combustion engine; a crankshaft connected to the piston by a connecting rod, the crankshaft arranged to rotate under influence of movement of the piston in the cylinder in accordance with an engine speed commanded by a throttle control; a junk head disposed opposite the piston proximate to a first end of the cylinder, the junk head comprising one or more compression or oil-sealing piston rings, the junk head arranged to be at least one of stationary in the cylinder and moveable between at least two positions to vary a distance between the junk head and a top dead center position of the piston at a rate governed by a control; and a first sleeve valve associated with a first port connecting to a combustion chamber defined at least in part by a head of the piston, an internal surface of the junk head, and the first sleeve valve, the first sleeve valve at least partially encircling the piston and arranged to open and close the first port by first movement between a first open position and a first closed position, the first movement comprising the first sleeve valve temporarily ceasing its motion in a direction aligned with an axis of the cylinder at the first closed position and at the first open position; characterized in that the rate at which the distance between the junk head and a top dead center position of the piston is varied is governed by the throttle control rather than by a speed at which the internal combustion engine is operating; and a first sealing edge of the first sleeve valve being urged into contact with a first valve seat at the first closed position such that the first sealing edge is closer to the first end of the cylinder at the first closed position than at the first open position.