Edelbrock head valve spring assembly

Well, since these are under the springs, they effect installed spring height because they set the bottom of the spring relative to the retainer. If the bottom moves up, and the top stays fixed as determined by the valve and seat and retainer and keepers, the installed spring height changes. The installed spring height is the actual length of the spring installed.

For example, if we put these .060" cups in place of an installed .040" shim, the installed spring height will shorten by the .020" difference.