Like its larger brother, the Wasp Junior was an air-cooled, nine-cylinder radial, with its power boosted by a gear-driven single-speed centrifugal type supercharger. Its cylinders were smaller, however, with a bore and stroke of 5 3⁄16 in (132 mm), giving a 27% lesser total displacement. The Wasp Junior used many parts from the Wasp and even had the same mounting dimensions, allowing an aircraft to easily use either the smaller or the larger engine.[2] The first run of the Wasp Junior was in 1929,[3] and sales began in 1930.