Has anybody measured the install height for valve springs on LS3 heads? Did you find inconsistencies from one valve to the next?

I've got a brand new pair of LS3 heads, and last night I had all of my valve springs off in order to shim them .030. What I discovered was that my installed heights aren't really all that consistent. They range from a low of 1.744" to a high of 1.756", with the average right at 1.750".

I haven't measured the other head yet, but I recall that when I measured that head initially I had a similar amount of variation.

 

.010" of variation like you listed could very well be factory tolerances yes. Or consistency in your measuring tool...dirt/oil under the seats ,etc

The intake and exhaust valve heights are often different depending on which valves you have in there. I've seen this on new GM heads...sometimes have to shim the intake springs different than the exhaust, and use 8 pushrods of one length and 8 of another if you want the preload dialed in exactly.

 

This is why you dont shim blindly. You shim off of coilbind!! Specific to every single spring and valve.

 

No doubt. Fortunately, in my case, I'm not shimming to a height that's anywhere close to coil bind, so as long as I don't have any sort of "abnormal" levels of variation, I can stuff my .030 shims in and be done with it, though on my tallest one I'll probably throw a .015 shim in also.

 

Then you need more shims, different springs, or a similar cam with more lift.

 

I'm shimming based on the recommendation that Texas Speed gave me for their PRC springs.