LSX Endurance Solid Roller Valve Spring Kit - High RPM & High Lift1. 300 OD Circle Track Endurance High RPM Spring Kit Use this specially design small diameter valve spring for your endurance applications like, Drifting, Circle Track, Endurance Marine. Specially designed and engineered to be a light weight high rate, high natural frequency spring. Reduce the amount of spring surge by increasing your spring rate, and reducing your mass. This is your package! Kits Comes Complete & ready to rock with: 1. 300 OD Dual