valve spring height question

CPMotorworks said

So your whole premise is based on who to blame when it fails.
Ever wonder why the same 911 spring is used on cams from .420" lift to .525" lift?
At the same 130 seat pressure?
Because we've all seen the failed cams with the flat base circle.....
So lets compare open pressures.
130lbs @ 1.900 IH -.400" lift=272 lbs open with Comps smallest cam
-.500" lift= 309 lbs open with Comps largest cam.
38 lbs of open pressure over the nose of the lobe difference from smallest to biggest.
Seems like a lot more important than 25 lbs on the base circle when the valve is closed...
But the OP will do what he feels most comfortable with, and that's ok.

Click to expand...

No, not my whole premise, just the one that can hurt the most, and one people don't think about when they cut corners or ignore recommended settings..
Your comparison of the open pressures is pointless and not what the issue is here. And your comment about the "flat base circle" shows you don't understand the real issues.
First having too much seat pressure can prevent the follower from rotating during brake in. That's how your extra 25 lbs/in ( 147 lbs/in total) can wipe the lobe , and that's why cam manufactures don't like high seat pressures during run in.
Second ,the highest acceleration rate of the valvetrain occurs right off the seat. So when you add more than needed seat pressure you also add to the deflection of the pushrods and the rocker ( especially in a stock valve gear). Not to mention added heat generated and wear.
One other problem with not using correct ( lower) installed heights is that you may be preventing going to a higher lift cam at a later date because you would run into coil bind. Then you have to do the whole valve height set up again , and no one likes to do the same job twice.