Abstract: An internal combustion engine having one or more compounded pairs of undulating volumes, such as produced by a piston reciprocating within a cylinder or tri-shaped rotor orbiting within an epitrochordial shaped chamber, hereinafter referred to for convenience as cylinders. A total of eight cycles or "events" occur withiin paired cylinders which are located side-by-side in as close proximity as possible so as to share periodically common combustion and provided with combustible fuel mixtures prepared externally of the combustion chamber through conventional means, such as carburetion or jet systems.