Very doubtful the studs being 5/16” is the issue. Stud quality (or lack of) more believable. But cant rule it out i guess but the spring pressure you have is not up there. Something else in the valvetrain and the geometry likely. Im running Hughes #1110 single springs (120# seat, 320#@ .550”) with Comp Cams 5/16” studs among other Comp valvetrain components on my EQ heads (1.6 rr and .517” lift) pushed slightly over 6000rpm often, many 1/8 and 1/4 mile runs and no issues. Id be looking at geometry, clearances etc
