Original: The hyper engine was a 1930s study project of the United States Army Air Corps, an effort to develop an aircraft engine capable of delivering 1 horsepower per cubic inch (46 kW/L) of engine displacement.
Simplified: The hyper engine was a possible aircraft engine model that could produce 1 horsepower per cubic inch of engine displacement. The term hyper engine was used only in the United States, where the Army Air Corps gave people money to make a hyper engine that had an area of 1,300 cubic inches.