These springs were purposely designed for those requiring a reliable spring for endurance racing applications, such as circle track or road racing. But they are also great for short track or drag race applications for racers wishing a longer lasting more reliable spring. Manufactured from race proven high endurance Alpha 1 material. All are cycle-tested at maximum valve lift to insure peak performance. Part number S608 and S623 also features an electro-polished outer spring for enhanced fatigue resistance.