Is this the measurement of the valve itself or the overall height including shims and spring cups if used? I am having a hard time picturing how to arrive at 1.800. I have to assume that the spring itself, setting on a table, is longer than the required 1.800 right? So, if I need 1.800 installed height, and I install the spring with the spring cup and retainer and locks, it should collapse to the height of whatever the measurement from the pocket of the head to whatever the retainer allows it to collapse?

 

That's one way of puting it.

Installed height = height of the installed spring.

Spring mics give the height a number.

Dean

 

An uninstalled spring has no tension. When installed to a specific height, it creates pressure to hold the valve closed. This is seat pressure. Installed height can be changed with shims, retainers or locks all designed to change the install height and spring pressure.

The install height is the distance between the head surface/shims/etc and the underside of the retainer.

You can increase the seat pressure by decreasing the install height with shims however you also decrease the maximum lift of the spring. If the spring is installed too tight, coil bind can occur at max valve lift.

Spring specs will give a seat pressure at a specific install height. They normally also give an open load pressure and height. Lets say your springs have an installed height of 1.800 and an open load at 1.300 and coil bind is at 1.140. The difference between open and closed is only .500" but that's not the restriction to valve lift. With coil bind, there's an additional .160" between open and coil bind however you can't go that far. Distance between open and coil bind needs to be a minumim of .060". That means there's an additional .100" of lift that the springs can take. Putting a .600" lift cam with these springs would be cutting it a little close of tolerances.

There are other factors that limit the maximum lift. The underside of the retainer may hit the top of the valve stem if the lift is too much. Installing longer valves and pushrods to install a higher installed height valve spring or to just shim the springs away from the valve guide is a way of correcting clearance problems.

 

So, to answer my question, If I take one of those spring mics and measure from the seat on the head to the bottom of the retainer, and find that the measurement is 1.850. If my spring card states that the spring needs to be set at 1.800, then I need to use .050 shim. Would that be correct.?

 

Yes. Just make sure the spring mic contacts the retainer in the same area as the valvespring.

 

OK, thanks guys!!!

 

not meaning to hijack this thread but ...
I've got a set of LT4 factory springs, retainers and keepers I'm planning to install but don't know what the install height should be. I've come across a number of 1.78" ... can anyone confirm this dimension or state the correct value?
Thanks