the guy was setting them up for a solid roller cam. since my engine is basically going to be a street engine those springs would be a little big. I suspect that to get my 15" of vac i will have to go conservative on my cam choice. I was tossing around the idea of hydraulic roller with rhoads lifters to get back some of my vac at idle. My tech inspectors barely understand what vacuum is let alone how to manipulate it.