Join Date: Apr 2002
Location: Minneapolis, MN
Valve springs are an often overlooked part of the total valvetrain combination. They shouldn't be, as they are as important as any component in the valvetrain, or for that matter, the whole engine.
Generally speaking, there are really not good and bad valve springs, any more than there are good or bad cams. There are only parts that do or do not match the rest of an engine combination, and therefore work well together or not. Certainly there are higher overall quality/durability springs versus economy pieces, but the there is more to it than just getting a "good brand."
Valve springs for flat tappet and roller cams for the same general engine application and rpm will be substantially different. Roller cam springs will generally have both higher seat pressures and higher open pressures; often they further have the ability to handle more lift. This is because the roller on the lifter interfaces with the cam in a geometry that allows both higher ramp acceleration velocity, and reduced lifter/cam friction. The more severe acceleration ramps enabled by roller lifters mean the valve is lifted further for a given duration than with a flat tappet. Higher velocities and greater total valve train range of movement means greater spring pressure is required to prevent valve train separation and valve bounce off the seat.
Roller lifter springs for a hot street, open track, or street/strip motor might have ~140 lb. on the seat and ~340 lb. open. These pressures are well-endured by the roller lifter, but would cause rapid wear on a flat tappet cam designed for the same engine application. Fortunately, the flat tappet lifter is lighter than the roller lifter and can be effectively controlled at somewhat lower pressures.
Both roller and flat tappet hydraulic lifters can suffer partial collapse of the lifter at high rpms with the attendant high spring pressures, especially those of a roller setup. As inertial forces become greater and greater with increasing rpm, at some point the internal plunger of the hydraulic lifter body will begin to collapse down into the body of the lifter as the oil cushion is forced out by the great pressures. High rpm photography/measurements have shown that hydraulic roller setups can lose as much at .050" lift when pushing the rpm envelope. This actually changes the effective duration of the cam (the .050" specs) and helps to explain the performance difference typically found between otherwise valve-motion-equivalent solid and hydraulic tappet cams. This phenomenon rapidly increases in severity as the spring pressures required to control the valve train reach and exceed 350 lb. open pressure. You don't need this kind of pressures for these applications with a flat tappet cam, and you should avoid any spring pressures higher than necessary. This is one of those places where more isn't better.
Best plan is not to guess at valve spring requirements. Only the cam grinder can specify the ideal springs for a particular grind. More than just pressure specs, the springs must effectively control the particular range of harmonics generated by the unique lobes of any given grind. Only the cam grinder will have data/tests to accurately match up a given grind with suitable springs/dampers. You may get lucky taking an educated guess based on lifter type, cam lift/duration, and rpm range intended...but why set yourself up for potential failure when the advice for the right specs is free from your cam supplier?
Last edited by amossm; 10-31-2002 at 10:37 PM.