There comes a point as rpm, valve lift, spring pressures and valve size increase, that a single spring is no longer up to the task of controlling the valves. This is when it is time to use a dual spring. Our springs are made in the USA. They come with Retainers and 10 degree locks. Good up to .700″ lift ( it is up to your machine shop to set installed height correctly)
You will either need to run without stem seals or buy comp cam 519-16 and howards cams cutter 92035 and 5/16″ arbor 92085. It takes about five minutes to modify the head to handle the smaller seals and can be done easily with a cordless drill.