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," Billy says. "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."
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."
Valve EventsOf the different valve events-intake valve opening, intake valve closing, exhaust valve opening, and exhaust valve closing-intake valve closing is the most important in terms of the rpm at which the engine will make peak power. "When you close the intake valve, air stops entering the cylinder," says Billy. "If you close the intake valve early, you will make more low-speed torque because less air escapes back into the manifold at low rpm, since the air has a slower intake-charge velocity and more time per degree of engine rotation to fill the cylinders. At high rpm, you need more time to fill the cylinder, so a later intake valve closing helps tune the engine more at high rpm, where peak power is made. The cam phasers found on L92 GM applications are great because they let you move the cam around to better tune at each rpm range."
Lobe Separation Angle
One of the most misunderstood aspects of camshafts is how LSA affects the power curve. Typically, wider-LSA cams have a wider powerband, reduced maximum cylinder pressure, decreased dynamic compression, and better idle quality and vacuum. On the other hand, tighter-LSA cams have a narrower powerband, increased cylinder pressure and dynamic compression, and reduced idle quality and vacuum. However, there are some exceptions to the rule. "As we found when testing our Thumpr cams, we can widen the power curve on a tight-LSA cam by increasing the exhaust duration," explains Billy. "The downside is that it will greatly decrease vacuum and is not a good path for EFI applications. Taking all these factors into account, it's not surprising that some cams in production motors today are on 120-degree-or-wider LSA."
Beehive Springs
Simple tweaks to a venerable design can yield big dividends in performance, and beehive springs are a perfect example. Elementary physics is why they work so well. "The difference in the active mass of a beehive spring compared to that of a conventional dual spring for the same application is more than the difference between a steel and a titanium valve in the same application," explains Billy. "Beehive springs take more mass off the top of the spring, which is the area that moves the fastest and the longest distance. Beehives are also naturally progressive in rate, therefore each coil vibrates at a slightly different frequency. This keeps the spring from going into resonance like a conventional spring and results in more of a self-damping effect."