Designed specifically for professional tractor pulling competition. Superior viscous damper design controls harmful torsional vibration across the entire rpm range. Reduce wear on engine components. Reduce risk of crankshaft failure. Improve timing. Unleash lost torque and horsepower. Competition built precision CNC machined and balanced high-grade steel components. Corrosion resistant black zinc finish with laser engraved clockwise and counter-clockwise timing marks. No maintenance required. Trusted by leading performance diesel engine builders worldwide. SFI 18.1 certified. Made in USA. NOTE: Requires Bolt Hole Drilling.