These Powermaster Powergens allow you to keep the authentic looks of a generator with the efficiency of an alternator. They put out 90 amps maximum with 65 amps at idle and 75 amps at cruise and are a simple one wire design. Powergen Cutaway View (Link) 65 amp idle, 75 amp cruise, 90 amp top end Pulley works with 3/8" wide belt Inside mounting ear-to-ear is 7" Overall length is 10-5/8" O.D. of case is 5" Fits 1955-1964 GM models (except with generator mounted power steering pump).