[Henry Schmidt]

Spring height specs are based on cam profile not engine size.

A good rule of thumb is .070" from coil bind at full lift.

Take valve lift and add .070" and that will be the installed height. It will also give you max spring pressure for the given spring.

If you take this calculated spring height and check the pressure at the height you will have installed pressure.
Something between 60 and 90 lb will be normal.

If you add calculated height and valve lift spec that will give you pressure over the cam. I like to see somewhere between 230 and 260 lb.

Some of the new valve springs offered on the market today give you an over the top pressure of more than 300 lb. My feeling is 300 lb is way too much (high pressure generates friction= heat which adds to parasitic loss and excess wear). That is why we came up with a valve spring formula that gives us 80-90 lb of seat pressure and only 240-260 lb over the top even with high lift cams.

It has been my experience that if you use this method and the seat pressure is over 60 lb there is no need for special valve spring unless an RPM in excess of 7500 is projected.