i was talking to a freind of mine who races rail cars, and he mentioned about shimming the valve springs to the proper seat pressure..

is this necessary? i have no idea what it should be. i noticed they do sell the gauges for it though.

i have a XE 224/236 cam with the matching springs sold by combination motorsports, the ones that require no machining to the head. i plan on revving the motor pretty high and may put a hydra rev kit in.

so what's the scoop on seat pressure?

 

You should have gotten the specs with you springs. They will tell you the installed height and coil bind I think. One will be an inches measurement and one will be a lbs. measurement. If you didnt get it with your springs then call Combo with the part# of your springs and they will give you all the info. But yes its very important to install the springs properly. Otherwise you may get valve float or premature coil bind

 

Shimming is usally necessary to set up heads properly. You want to use shims to get installed height that provides the desired seat pressure. Obviously, there needs to be enough height left in the springs to avoid coil bind. The specs will list xlbs @ y" installed height. But you can install them either taller or shorter depending on the needs of your combo.

The best way to do this is with the use of a spring tester, but if you don't have one you can just use the manfacurers specs to determine the installed height you want. To do this you need the spring rate (also found in the specs). Example: your springs have a rate of 300lb/in and are listed as 150lbs seat pressure at 1.800" installed height. If you want 165lbs of seat pressure, you must install them at 1.750". The additional 0.050" of compression will give you 15lbs more seat pressure because (300lb/in)/0.050" = 15lbs.

Rich Krause