Abstract: A gear set is disclosed having a guide, such as a cam, engaging the output shaft of the gear shaft and being indexed thereby. The guide drives one or more followers which in turn drive one or more interfaces of a differential gear set. The output shaft may be driven by a third interface of the differential gear set. The followers may likewise engage piston assemblies in order to control the piston assemblies during execution of a process such as a four stroke combustion process, or other process involving compression or expansion of a gas. The piston assemblies are enclosed within a housing defining an annular chamber, such as a toroid. Apertures formed in the housing allow exhaust gases to leave and air to be taken in. In one embodiment, a hyper expansion port is formed in the housing to release a portion of the air during the compression stroke in order to decrease the pressure of combustion gases.