High-Lift Lobes
A growing trend is packing a whole lot of lift into relatively short-duration camshafts. This has led some enthusiasts to postulate that lift takes precedence over duration when spec'ing out a cam, but that isn't necessarily the case. "Now that improvements in valvetrain technology allow increasing lift with short-duration cams through steeper lobes, we tend to do that more often," says Billy. Modern cylinder heads flow very well in the 0.500- to 0.650-inch range, but that wasn't always true a few years ago. "It used to be the case that we needed large-duration cams to get into that lift range. Now we can run shorter-duration cams and still lift the valve into the range where the heads flow best. This gives both the drivability missing in large cams and the power we could not previously achieve with short-lift cams."
Installed Height
"Many years ago, springs were not designed around the solid stress state, when the coils are pressed together. That has since changed, and the damping effect of springs is used to reduce any surge waves resulting from a rapid valve opening as the spring approaches a solid state. If you do not check the solid height of the spring and the installed height, then you can't control how close you get to a solid state. Likewise, if you don't check installed height, you can only guess how much load you have on the seat or anywhere else to control the valve. Obviously, if you try to lift the valve past solid height, then something has to fail. However, now we know that if you are too far away from solid, you will not be able to use the coil interaction over the nose to reduce surge. Depending on the application, it's ideal to have the spring come to within 0.060-0.120 inch of solid over the nose."
Lofting
Some industry insiders tout lofting as a hot new fad in engine building, but not everyone is convinced. Lofting is a method of increasing lift where the lifter momentarily loses some contact with the nose of the cam lobe. "We have yet to find an application in which you wouldn't be better off with the increased lift designed right into the cam or rocker arm instead to allow controlled valvetrain operation," Billy opines. "Lofting does not increase duration, and in fact, the increased loading associated with it often decreases duration at high speed. Hence, it is not a poor man's variable valve timing system as thought some 10 years ago in NASCAR."