Features a retainer design with no shim capture for use with stock Polaris cam buckets and a recommended setup if banging on the anti-lag. BC valve springs by PAC Racing are wound from only the highest grade, super clean, chrome silicone alloy and feature proprietary processing procedures for consistent pressures. BC retainers are machined from premium 4140 chromoly steel for "set it and forget it" wear characteristics. Beehive spring keeps retainer lightweight. Also requires BC3991 valve stem seals.