Drop-in install, no machine work. Designed for high rpm, 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 6AL4V titanium alloy for added valve control above 10,000 rpm. 

Note: If running endurance, high mileage desert or trail riding, use BC0920S the utilizes the 4130 chromoly steel retainer.