The sole purpose of the valve spring is to force the valve to follow the path of motion that is dictated by the camshaft lobe. Excessively stiff springs will steal torque from the engine and increase component wear while a spring that is not stiff enough will allow the valve to “float” or loose contact with the cam lobe. Valve float will eventually lead to component failure. The spring must also have enough available compression distance to allow the full amount of valve lift that is produced by the cam. Coil Bind is the term used to describe a condition of too little compression distance where the spring “bottoms out”. Coil bind will also lead to component failure.
The reasons that a cam would require a change of valve springs are: 1. more valve lift than the OE spring can accommodate before coil bind. 2. A quicker valve opening and closing rate that requires more spring force to keep the valve from floating. Several other factors that dramatically affect valve spring choice are maximum RPM and valve weight. The force produced by the spring must control the kinetic energy of the valve. Kinetic energy is equal to mass times velocity squared. If you increase your rev limit by only 500 RPM, spring force at full lift must increase by approximately 10%. Usually the spring safety is 10% or slightly more but if you changed the cam and also increased the rev limit you may now have created a valve float problem. It is the same when you replace an OE titanium valve with a steel valve. The steel valve weighs 75% more than the titanium valve that the spring was designed for. Your spring must now be 75% stiffer or you must lower your rev limit by 15%! This is why it is very important to use the correct spring as recommended by your cam designer.
Valve Lash (clearance)
Always run the recommended valve clearance. Cams are designed with ramps that “gently” take up the clearance and then “gently” set the valve back into place on the valve seat at closing. If the clearance is larger than recommended the ramp may not be able to do its job and the valve will receive very rough treatment. This can potentially cause component failure.