CHEVROLET LS1. This kit includes PAC 1204X Dual Spring (x16), Kelford Titanium Retainer (x16), Steel Locator (x16) and Viton stem seal kit (x16). PAC-1204X RPM Series Dual Spring. Premium quality Japanese spring steel wound in USA by PAC. Made with advanced heat treatment processing and surface finishing techniques (nano peening) to extend fatigue life. High spring frequency to allow for better spring surge control at high rpm. 145lb at 1.800″ installed height. 385lb at 0.650″ valve lift. Coil bind (spring solid height) 1.000″.