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.

The source of the listed information is the corresponding article at Japanese Wikipedia.

In 1956, Prince developed a flat-2 engine, the FG2D, for their DPSK (later CPSK) concept car. It displaced 601 cc and produced 24 hp (24 PS). The engine suffered excessive vibration and noise issues and was replaced with the FG4C engine.

Prince developed the FG4C, a flat-four displacing 599 cc and producing 38 hp (39 PS), as a replacement for the FG2D. The FG4C was used in the 1957 CPSK concept.

1.5 L (1,484 cc) diameter X stroke: 75 mm × 84 mm (2.95 in × 3.31 in), OHV

1.5 L (1,484 cc) diameter X stroke: 75 mm × 84 mm (2.95 in × 3.31 in), OHV

1.5 L (1,484 cc) diameter X stroke: 75 mm × 84 mm (2.95 in × 3.31 in), OHV