This 1993-1997 GM LT1 BBK Performance Under-drive Crank Pulley is designed as a piggy back for the OE factory harmonic dampener. It is a direct bolt on pulley and will retain full cooling and charging characteristics. This BBK under drive crank pulley kit is an easy way to free up an average 8-12 horsepower in under 30 minutes. Each kit comes with complete installation instructions and hardware.