The valve springs on a modified engine are subjected to extreme stress from high RPM operation, high lift valves and excessive heat. springs for this type application must be manufactured from special alloy wires such as chrome vanadium, chrome silicon and in extreme applications, Vasco jet 1000 or titanium. In addition, racing valve springs must receive special treatments to prolong life, prevent breakage and loss of tension due to set. These special treatments include heat setting, shot peening, deburring and coating.Springs for racing applications must be carefully designed to ensure that the maximum stress limits of the wire is not exceeded during operation. Springs must be designed with the highest possible natural harmonic frequency consistent with the stress limits of the wire and the dimensional limits imposed by particular application. Since it is seldom possible to raise the natural harmonic frequency of the spring high enough to eliminate harmonics during operation without over stressing the wire, flat counterwound dampers or inner and outer springs with an interference fit are used to reduce the amplitude and duration of spring harmonics that may occur. There are two basic types of valve springs and common use for racing applications; the constant rate spring, which has symmetrical coil spacing and will increase in pressure at a given rate through its entire travel; and the variable rate spring that has progressively closed space coils at one end and will increase in pressure progressively. Both designs are sound and can be adapted to most applications.