Cant tell you the difference but its for different CPL numbers (the number used to determine the hard parts such as injectors, cam, pistons, and fuel pump/fuel pump calibration). different CPL's are used to also differ the same engine (6bt's, ISB's, ISC, ISX, etc) with different HP and TQ levels for the application they are designed for. If youre still interested I could look up the different CPL's that these cams fit. if you have the ESN (engine serial number) with each cam, I can tell you exactly what hp and CPL they are rated for