BBK Aluminum Under drive Pulley Kit for Ford Mustang GT/Cobra 4.6L - 3 Piece is made from aircraft quality aluminum alloy. These BBK under drive front accessory pulley kits are one of the easiest ways to free up an average of 8-15 horsepower in under 30 minutes. These BBK pulley kits are designed as direct bolt on replacements for the current factory pulleys and retain full cooling and charging characteristics.