An opposed piston engine includes a cylinder having a cylinder wall, and a pair of opposed pistons, Each face of each piston of the pair of opposed pistons has a top plane and a recess formed therein, each recess comprising a first surface defining part of a cone, the cone defined by the first surface of at least one of the recesses having a longitudinal axis that defines an angle equal to at least one half of a cone angle of the cone with the top plane.