valve spring pressure at lifter/lobe interface

[hotrodford]

My question: how much spring pressure at the lifter/lobe interface is too much.

Same project as a previous question I asked (351 C valve size) about my Boss 302 vintage road race car. I have a solid flat tappet cam (it is an older Crane OTS 351W cam) with 5 years of racing (shift at 6000-6500 when running easy and 7500 when pushing it).  Recently checked lifter faces and all look as good as new.  In reading one of the FE threads, concerning roller lifters, the importance of proper valve spring pressures was referenced.  I got to thinking about the relationship of rocker arm ratio and the effective spring pressure at the lifter/lobe interface.  In my own case knowing the spring pressure at max valve lift multiplied by the rocker arm ratio and I get a number well in excess of 600 lbs (640 to more accurate).  Never really thought about that before and that number stunned me just a bit.

The heads I am taking off the motor have a 1.9 installed spring height.  The heads I am switching to the springs would have a 1.8 installed height if I didn't do anything change that.  That .100 inch change in spring height would change the pressure at the lifter about 60 lbs. 

My curiosity has me asking the question of "how much spring pressure at the lobe/lifter interface (considering the cam I am using) can a flat tappet cam operate at?

Thanks,
Dennis




 

[blykins]

Lot of variables there:  if the cam is nitrided, what the lifters are made of, if they oil out the botto, etc. 

[hotrodford]

No special features for the cam or lifters (no nitriding and no oil holes).  What I refer to as an off the shelf "standard enchilada"!!  It is Crane part number 440981, grind number F-252/3574-2S-6.  I used "break in oil with a set of Ford (used) springs (single) off of 351 C heads.  Have used VR1 10w30 ever since. First used the "conventional" then went to the synthetic. 

[blykins]

I really don't run plain-Jane stuff over 340-350 lbs over the nose.   I've ran nitrided cams and EDM lifters at ~425.   

[My427stang]

If you are asking about using your springs with the new installed height, depending on the valve diameter and lock style, you can buy some of that back with a +.050 lock.  Potentially combined with a change in shims (if you have some in there), you may be able to get close.  I have seen even taller locks, but I wouldn't call them performance pieces, and very limited options. 

Regardless, I'd measure every spring and valve for instaled height and pressures because you are also taking away coil bind clearance