COMP Cams 1411-8 Magnum Roller Rocker Arm with 1.72 Ratio and 7/16" Stud Diameter for Chevy Big Block Engine, (Set of 8) For big block chevy applications, 7/16 inch stud, 1.7 ratio Roller tip reduces friction while stiff design and superior ratio accuracy yields more effective valve lift 15 to 30 horsepower increase over stock rocker arms Use in any applications with less than 350 lbs. open spring pressure Made from 8620 chromemoly steel that will not flex