Just quoting their numbers from the internet of course I believe it was like 145 and 360 on the spring pressure and a Max of 600 lift. I thought prh also said one or two Springs were a little weak but that of course he said was if I believe you were trying to do this Max 600 lift? I'm at about a 525 lift right now with the 1.6 to 1 rockers. Which would probably be plenty for the unported heads anyways? Also if I went to a bigger cam I don't see myself going past 575..