Made specifically for racing applications, these pulleys are designed as a system, working together with current power steering pump pulley to provide the CORRECT ratio. This pulley ratio ensures that the power steering pump and the water pump operate within the optimum RPM range as specified by General Motors. Currently available pulley ratios do not provide the correct ratio for use in racing where the engine RPM differs greatly from street applications. In order to provide the correct ratios the crankshaft and water pump pulleys are smaller in diameter than the pulleys they replace. As a result, the weight and inertia of these pulleys are reduced, increasing the acceleration capabilities of the engine. (Note: Allstar #ALL86120 (sold separately) belt required for crank to water pump. Allstar #ALL86122 (sold separately) belt required for crank, water pump and power steering. Lower pulley will work with either water pump pulley #ALL31040 or #ALL31050 (sold separately) without the need of any spacers. NOTE: Both Water Pump and Crankshaft Pulleys are shown, but are sold separately.Pit Stop USA offers Allstar Performance Aluminum 2 Groove Chevy Crankshaft Pulley - 4-3/4" Diameter ALL31030 at low everyday prices. Be sure to check out all of our products from Allstar Performance including Allstar Performance V-Belt Crankshaft Pulleys.