Valve spring rate

[fredo11]

I would like to know what the application for using spring rate in lbs./inch. would be used for. How are you able to compare valve springs and know that the proper spring has been chosen. Tech guys seem to vary on what they would use from day to day. But I would still like to know the " how's and why's " of spring rate as related to valve springs.
Thanks in advance.

[OldSStroker]

I would like to know what the application for using spring rate in lbs./inch. would be used for. How are you able to compare valve springs and know that the proper spring has been chosen. Tech guys seem to vary on what they would use from day to day. But I would still like to know the " how's and why's " of spring rate as related to valve springs.
Thanks in advance.

If you know how much load it takes to control the valvetrain "over the nose" at the max rpm you are running, and how much load it takes on the seat to control the valve bounce at closing to an acceptable level, you have two loads and a distance (valve lift). From this you calculate a spring rate. Example: 400 lbs. over the nose, 150 lbs on the seat and .600 lift. (400lb-150lb)/.600 in. = 417 lb/inch. If your system needed 600 lbs over the nose but still 150 lbs on the seat the rate needed would be 750 lb/in, about 80% stiffer than the first spring.

The catch is, as you said, knowing what is needed to control the valvetrain. Some simulators can give you a basic idea if you input the correct weights and stiffnesses. Testing the valvetrain on a Spintron will tell you whether you have enough spring, as well as all the resonant points, etc. I suppose some folks with lots of Spintron time find a valvespring that works, then try "softer" or lower rate springs to find th minimum acceptable. Most folks err on the "too much" side which is a safer way to prevent contact of valves and pistons or excessive bouncing on the seat, but it's harder on the valvetrain.