Proflow Alternator Pulley, V-Belt, 80mm OD x 17mm ID, Billet Aluminium, Black Anodised, Suit High RPM Engines - PFEP8869Part Number: PFEP8869 Proflow 80mm billet aluminium alternator pulley is a good mid range diameter pulley for a street driven high rpm engine. This still considered larger for high RPM engines. (most std pullys are around 50mm). If you want to further protect you alternator from overrun , you may consider using our PFEP8868 which is bigger again. Example: if you are turning 7000rpm and have a 6 inch crank pulley with a 2 inch alternator pulley, your