Kit is intended for OEM shim in retainer setup. 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. Type BC1950 Dual Free Length 1.572" Outer/1.339" Inner Seat 1.265" @ 76 lbs Open 0.850" @ 192 lbs Coil Bind...