Engine Identification B3.9, B4.5, B5.9 Industrial Page E-2 Section E - Engine and System Identification NOTE: If the engine dataplate (1) is not readable, the engine serial number (2) can be identified on the engine block above the oil cooler. Cummins® Engine Nomenclature B5.9 The model name provides the following engine data: B = Engine series 5.9 = Displacement in liters. B3.9 The model name provides the following engine data: B = Engine series 3.9 = Displacement in liters. The Cummins engine nomenclature provides the data as illustrated in the graphic.