After facing the 16 new Federal Mogul valves and machining the valve seats, Rubin checked and set the spring height and pressure. Both were adjusted with shims installed at the spring seat. If you’re running a radical camshaft, you need stiffer springs that will handle the punishment. Likewise, if you’re running a mild camshaft, springs that are too stiff will ultimately ruin the lobes. Spring pressure and lobe profile must be a compatible marriage.