That's a good question. I don't know it the limitation is in the hydraulic parts or in the roller itself.
I have heard somewhere that hydraulic roller camshafts have other style ramps, demanding very small lash settings if used with solid lifters.
I was just on the phone with a tech guy at Hughes, doing the best I could with my limited English lingual skills.
They said 138/369 lbs is fine for their cams. They would recommend a spring with 145/358 lbs if the springs in the head weren't already there. The choice between their lifters 5006, 5006S or 5007 are more about getting it quieter or getting "variable duration". All of them should cope with the pressures.
From this point of view I have to judge if my cam and lifters are as good as Hughes... I do believe they are cast core cams as well
