An engine block is disclosed in one embodiment having a cylinder shape bore, which forms the outside wall surface of a cylindrical air chamber. Radially outwards from the cylindrical air chamber there is an annular shape combustion chamber, which has a circular inner wall surface, circular outer wall surface, closed annular shaped top surface, and an annular shaped open end opposite of the top surface. The bottom end of the circular inner wall surface of the annular shape combustion chamber and the bottom end of the outside wall surface of the cylindrical air chamber defines an annular shape surface. This surface fits inside the annular shape air chamber in the piston assembly. In one embodiment, in the lower part of the circular inner wall surface of the annular shape combustion chamber there is a circular groove for an oil scraper ring of conventional design.