Abstract: A four-stroke internal combustion engine for the otto and diesel cycle, characterized by incorporating a valve distribution for engines that use one or more ports near Bottom Dead Center. The four-stroke internal combustion engine comprises one or more cylinders each with a piston movable therein to define a combustion chamber and a port provided in a wall of each cylinder. The port is openable independently of an inlet valve and an exhaust valve to provide an additional route for the discharge of air or fuel/air mixture.