Chevy trucks polished aluminum billet 6 groove serpentine crank and Alternator pulleys set. These are for the Chevy 1988-1993 trucks 454 7.4L engine. The pulleys are CNC-machined from the lightest, most durable materials possible; 6061-T6 aluminum billet. The pulley are 25 percent underdrive. The crank pulley are in 5 7/8" diameter. The Alternator pulley are in 3" diameter.