A rotary engine includes a casing having a first circular boring and a second circular boring smaller than the first circular boring. The first circular boring interconnects with the second circular boring. A piston rotor can move in a rotating manner within the first circular boring in the casing. A power head, ported to pass exhaust gases through a hollow center shaft, can move in a rotating manner within the second circular boring in the casing. The piston rotor and the power head can be coupled via a gear system to properly rotate during operation, with the piston rotor rotating counterclockwise and the power head rotating clockwise, or vice versa.