[FED 387]

Serpentine belts the groves run the length of the belt--- Cogged belts the grove run across the belt--- cogged belts use pulleys that look somewhat like gears -- you can also change the rpm of the pulley ever so slightly by altering the tooth count of the pulley- dry sump and fuel injection pumps are good examples of cogged belt uses---- while serpentine belts use pulleys that the groves look like circles on the surface of the pulley and you are restricted to only a few different diameters -most modern automotive systems use them generally in conjunction with either an idler or tensioner depending on the application