March Performance Ford Windsor serpentine kits are made to fit perfectly and handle high torque and vibration. Matching serpentine pulleys are precision CNC-machined from 6061-T6 aluminum and have a maintenance-free, clear powdercoated finish. These high-tensile strength pulleys will not fracture like common cast pulleys, since they are made for much longer wear. The high-wear areas are hard-coated to “65” Rockwell (harder than steel)! Street rod ratio increases water flow and fan speed, which helps at critical low-speed driving.