Speedmaster Flywheel for SBF 289, 302, 351, 351C, WindsorExternal Balance 28 oz.164-Tooth These Procomp Electronics billet steel flywheels are fully CNC machined from a high tensile aircraft material billet steel. The high carbon steel material is incredibly strong and can withstand the rigors of the most extreme engines, drivers, and road conditions. Procomp Electronics 30 lb. billet steel flywheels. Most are drilled for both Borg & Beck and Long-style clutch assemblies.