Valvesprings need to be carefully matched to the specific camshaft in order to obtain maximum advantage from the cam. This is a dual spring with both an inner and outer spring plus a small, flat wire damper that is not counted as a spring.
Why You Need To Upgrade The Valvesprings
This chart is easy to understand once you know a little bit about valvesprings. Load at installed height refers to the amount of pressure in pounds created by the spring with the valve closed at a given installed height. The installed height is the distance from the bottom of the retainer to the spring seat location on the cylinder head. Load at maximum lift is the pressure created by the spring across the nose of the cam at its greatest valve opening. The spring rate is the amount of load in pounds created for every inch of travel the spring is compressed. If you know the load at both the closed and open points, you can determine the rate. Subtract the installed load from the open load and then multiply by the lift ratio (lift ratio = 1 divided by the max valve lift). Using the 939 spring as an example: 420 - 167 = 253 x 1.85 [1 1/4 0.540 lift = 1.85] = 468 pounds per inch (lb/in) spring rate. Coil-bind refers to the height of the spring when it is fully compressed. It's critical that the engine builder allow a minimum of 0.060 inch of clearance to coil-bind. We chose spring pressures higher than Comp's recommendations to ensure that the valvetrain would not go into valve float during testing.
Note the radical increase in seat pressure for the mechanical roller spring application. The hydraulic flat-tappet and roller springs both use a seat load of roughly 160 pounds. But when we get to the mechanical roller springs, the seat pressure jumps to 240 pounds at the same installed height. That's a 50 percent increase in seat pressure and a 59 percent increase in load at max lift. This is necessary in order to fully control the much higher acceleration rate and valve velocities achieved by the mechanical roller lobe working on the valves. As these opening and closing rates increase, they create much larger forces on the valve that must be controlled by the valvesprings.
| Valvespring | Load @installed ht. | Load @ max lift | Rate (lbs./in.) | Coil-bind(in.) |
| Comp PN 928, dual | 153 @ 1.900 | 330 @ 0.500 | 354 | 1.160 |
| Comp PN 939, dual | 167 @ 1.900 | 420 @ 0.540 | 468 | 1.225 |
| Comp PN 943, dual 240 @ 1.900 | 557 @ 0.575 551 | 1.150 | | |