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 1.9 L (1,862 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. These are unrelated engines and are documented at the Nissan G engine page.