Rotating your engine to the compression stroke as soon as you come off the track will lengthen the life of any spring. The head temps on most engines reach 400, 425 to 450 degrees. Your springs are around the same temp. The engine could stop with one of the valves open which has the spring compressed and as it cools could loose tension, especially the Exhaust spring because it gets hotter than the Intake. This way both springs cool down in a more relaxed position and should remain the same tension for longer... I have a more in depth write up about springs on our Facebook page.