Specifically for short or Corvette water pumps, pulleys work with power steering pump and pulley to provide a ratio within the GM specified RPM range. Race engine RPM differs greatly from street engines. For 30% less water pump speed and reduced weight and inertia, the crankshaft and water pump pulleys are smaller in diameter than standard reduction pulleys. Acceleration capabilities are greatly enhanced. Water Pump Pulley, Corvette Pump With 3/4″ Pilot hole 6-5/8″ diameter, Crankshaft Pulley (4-3/4″ Diameter. Items included, upper and lower pulleys, spacer kits, vee belts. Please e-mail with questions.