So i just purchased some stock 243 heads. The heads have lunati double springs good for 650 lift installed. I believe they have also had a valve job done.I was looking at the springs and the springs have shims installed. The shims say "V.S.I. 203". I'm not very familiar with shims since i haven't used a cam that required them.

What size are these shims?

Do they affect how much lift the springs can can take?

What cam setups require shims?

Thanks and any help is greatly appreciated

 

Shims are used to set spring installed height. If set-up properly then the spring can handle its max rated lift. So actually the shims make it handle more lift safetly, bc its set-up properly. Shims have nothing to do with cam selection, its only about making sure the spring is installed properly on the cylinder head.

 

Shims can also increase seat and open pressures. My heads from WCCH have the intake valves shimmed more than the exhaust valves since I'm running a turbo...

 

Not sure who set them up before you bought them but if they were a reputable shop and they sorted out what shims were required you may be OK. The advertised amount of lift for a valve spring is a rather nebulous number and for LSx setups typically based on 1.800" installed height. My stockers were less then 1.800". You really need the installed height, valve lift and clearance values to the seals, etc. to ensure all is OK. Don't go by just the value 0.650. If these were my heads I would disassemble at least one cylinder and measure the installed height so that the amount of lift, seat and open values can be calculated.

 

How would i go about measuring the installed height? A Digital caliper??

 

Valve spring micrometer. Here is mine:

Install instead of valve spring with retainer and locks, then measure. The type of spring will determine how you measure, i.e., the retainer size may or may not fit on the measuring surface.

 

^ that thing is cool