Technical information

All spring specs are measured with a retainer installed and measured on a flat spring base for both inner and outer (no raised or lowered inner spring step) Check with us first if you intend using a dual spring with a raised inner step. 

The specifications given are mean values, so one can reasonably expect to find springs on either side of any given specification. Spring pressures are within tolerance if they are within plus or minus 8% of the given mean value. Solid heights are normally plus or minus .030. Diameters are normally plus or minus .010. 

There are essentially two techniques and criteria that come into play. The first relates to either FLAT TAPPET or HYDRAULIC lifter cams, The second is the ROLLER lifter cam.

In flat tappet applications, seat pressure is a major consideration. Seat pressure is the valve spring pressure placed on the valve in the closed position. A lack of seat tension allows the valve to bounce off the seat on closing impact. 

For engines that will routinely need to RPM around 7000-7500 it is generally an accepted rule to keep this pressure to around 140lbs, assuming the camshaft and related components of the engine are designed for such RPM.

The second is obviously the ROLLER lifter cam. With hydraulics lifters, this pressure is better left to about 120lbs on the seat, with again making a similar assumption on the related components.

Maximum open pressure for most (BUT NOT EVERY) flat tappet application is around 360lbs open. Hydraulic lifter applications have a maximum open pressure of around 320lbs.

Valve float can be caused by over-revving of the engine or by inadequate open spring pressure, resulting in a lag in valve gear components where they fail to follow the cam profile.

In either of these camshaft set ups proper break-in is necessary, and typically about 10lbs of pressure could be lost from the initial assembly specifications due to settling of the components.

Loads beyond 160lbs of seat pressure or 390lbs open pressure will exceed the safe margin of wear between the heat- treated lifter face and the camshaft.

Open pressure above 330lbs requires light spring break-in.

We recommend .060 thou is the absolute minimum clearance between total valve lift and coil bind.