Cam lifter questions

[Bad70sbchevy]

I'm doing an engineering design project for school on designing a high rpm hydraulic roller lifter for a small block chevy. I was wondering what a lifter's seat height refers too? Is that the distance from the tip of the lifter where it contacts the cam to where the pushrod contact the top of it, or is it the overall lifter height? Also I was wondering what causes hydraulic lifters to lose power at high rpm. I always thought that it was because the lifter assembly collapses at high rpms, but I see that sometimes they will pump up at higher rpms. Is the later from not running high enough valve spring pressures? Just curious and thanks in advance.

[Rannos]

As I have always heard it hydraulic lifters tend to pump up at higher rpm's and cause valve float. As I understand it's more from a build up off oil pressure in the lifters then weak springs. Plus a Hydraulic roller lifter is just plain heavier then a solid roller in most cases. Saying that I have seen some LS motors spin 7,500 with hydraulic roller set ups. Not sure what all has been done but it's impressive. I think Super73 said he shifts his LS some where close to 7,000 with hydraulic roller set up maybe he will chime in and tell ya whats needed to spin'em that high.

Jay

[Blue Rat]

To much valve spring pressure would collapse a hydraulic lifter. Hyd camshafts have less radical lobe ramps. You need increased valve spring pressure to get up in the higher rpms to keep the valves seated for a solid roller lifter.