The Prince G-series engine was the company's only straight-four and straight-six engines which began production in 1955. A number of variations were made, with both OHV and OHC heads. A diesel four-cylinder with 1862 cc was also built, called the D-6. The G series was used in the Skyline, the Laurel, and the Gloria from the 1950s to the early 1970s.Note that, prior to its merger with Prince, Nissan also made a G series of engines.