Performance Valve Springs and Retainer KitThe XDP Performance Valve Springs and Retainer Kit XD386 are a perfect upgrade for your modified 2001 2016 GM 6. 6L Duramax. Camshaft upgrades and other modifications that increase boost require more valve control. The XDP Performance Valve Spring feature a conical design for better valve control than a standard straight spring. The conical design also allows for smaller and lighter spring retainers. Each spring undergoes a stress relief process and