When To Go Custom
According to Billy, cam manufacturers have done most of the homework for you. He recommends off-the-shelf camshafts whenever the application has something available for it that was designed with a similar application in mind. "These cams have a great deal of testing and are going to be better all-around performers than a custom cam 99 percent of the time," he states. "If we could make a better cam for a typical 383ci small-block Chevy, a ZZ4 crate motor, a 5.7L LS1 with aftermarket heads, or even late-model dirt-track and Super Comp-style NHRA applications, you can bet we would already have that part tested, verified, and included in our next catalog. However, chances are, if you're building a turbocharged NASCAR-style SB2 Chevy for a Suburban that you want to take on a cruise or bracket race, we are going to need to grind something custom, since you're doing something very unique. Likewise, we do custom grinds on many land speed and 24-hour endurance racing camshafts." Talking to someone at a cam company you trust is the best way to figure out whether or not you need a custom cam.
Solid-Roller Reliability
"Originally, solid roller lifters were designed for high-rpm race use," Billy says. "The only source for oiling the needle bearings was from oil thrown up by the crank. That works great at speed, but not so well near idle. The same lifters that lasted for several seasons in bracket and circle-track race cars were failing more quickly just going to the local cruise night and back. The other factor was spring load. Most of the older roller cams were designed for use with high spring loads. This helps keep everything under control at high speed with an aggressive cam, but greatly increases the load at low speed. The solution was twofold. First, we totally redesigned all of our roller lifters, both street and race, so that any lifter we sell with an oil band has a small hole feeding oil down to the needles. At the same time, we greatly improved the steel used for the axle while providing stricter control of the needle sizes to better distribute the load. The second part of the solution was to develop new profiles and springs for street roller use. These new profiles work great in the 2,000-7,000 rpm band while requiring far less spring pressure than the older race profiles. Together, these changes make it so the only maintenance consideration in buying a street roller from Comp Cams is whether or not you want to have to set and check lash. I recommend going through and checking the valves along with your oil changes. If you run Poly-Locks, this is probably overkill. Once you know what the engine sounds like, you will most likely be able to distinguish the tick of loose lash."
Measuring Duration
Cam manufacturers publish both advertised duration and duration at 0.050 inch of lift, which can be a bit confusing, but the difference between the two figures is simple. Advertised duration can be given at any lift point. Cam companies pick different points at which to measure, making advertised duration figures relatively useless. "A simple measurement was needed to keep everybody honest about how big their cams really were, and that's how duration at 0.050 came about," explains Billy. "Low-lift numbers between 0.001 and 0.020 inch tell an engine builder a great deal about vacuum and responsiveness, while high-lift numbers greater than 0.200 inch tell an engine builder more about power potential. The 0.050-inch number is relatively easy to measure with a dial indicator and a degree wheel. It does the best job of predicting the operating range of a given lobe in a specified application." Note that this is tappet lift and not valve lift, so those numbers can tell a very different story, depending on rocker-arm ratio.
Spring Pressure
Like choosing a camshaft, going with valvesprings that have produced good results in applications similar to yours will often suffice. On the other hand, if your combo isn't exactly mainstream, it's not a bad idea to seek expert advice to avert potentially catastrophic engine failure. "I know people want some sort of rule of thumb when selecting a set of springs, but unfortunately, it's not nearly that simple," says Billy. Load is just one of the factors that need to be considered when selecting valvesprings. "A lighter [mass] spring with less load is often far better than a fat spring with more load," Billy says. "There is also a tremendous consequence of the spring's natural frequency, the speed it vibrates at when struck by an outside force. This is another place where you should really trust the cam company to tell you what spring a certain lobe profile likes."