In this List of Perkins engines, family type refers to the two letter designation Perkins gives each engine. This nomenclature was introduced in 1978 under Perkins' new engine numbering scheme, where the family type is encoded in each unique serial number. Engines that went out of production prior to 1978 may have been retroactively assigned a family type to expedite parts support (this is the case with the Perkins 4.107). Some engines never entered production, such as the Perkins 4.224, but were assigned a family type.