Establishing multiple points of a cam's lift over duration on a graph like this shows us another important consideration to mind when evaluating a cam's characteristic-ramp speed. Ramp speed determines how fast a valve is opened or closed and plays a crucial role in maximizing efficiency-and isn't something reflected in lift/duration ratings. Going back to our graph, we see that CAM A boasts the longest duration, but has slower ramp speeds than CAM B. The secret to efficient cams is in how fast they can open and close a valve, pulling and trapping air in the cylinders. Think of holding a bag away from your face and trying to blow air into it. If you blow softly you may fill the bag, but slowly. And if you don't immediately close the bag when it fills, the air will revert back into the atmosphere. But if you blow quickly and close the bag as soon as it's inflated, you'll trap air inside more efficiently. A well-engineered cam causes a valve to lift off its seat quickly, maintain a lofty lift and return quickly, all without slamming back into its seat on the way down or necessitating the need for overly stiff valve springs to prevent float.
Lobe And Seperation
A look at our second graph will help us understand another important term defining cam characteristics-lobe separation. Lobe separation angle (LSA) is a measure of the distance between the peak intake and peak exhaust lifts, in degrees of rotation. In SOHC applications, the LSA is fixed; overlap is ground into the cam, and intake and exhaust cam timing cannot be adjusted independent of each other. In DOHC applications, intake and exhaust overlap can be made variable through adjustments in cam timing via adjustable gears or variable valve timing (VVT). Just as a cam with more aggressive lift and duration numbers can flow less than one rated more conservatively, so can two cams with the same lift and duration have very different overlap properties, even when paired with the same exhaust cam and timed the same. The equation just got more complicated.
A camshaft is a very simple component-a shank of steel with no moving parts. Needless to say, it's easy for any manufacturing company to reverse engineer and mass-produce a successful design. "But try going to those guys for advice with a build, or to get help tuning one of their products," suggests Dave, jokingly, "And good luck getting them to stand by their product when it fails." Not only to be read as one man's incentive to buy his product over another's, Dave's words underscore the intrinsic goals of advancement all genuine R&D companies have for their industry. With the knock-off companies hot in chase, their successes demand they stay at the forefront of development, to constantly break new ground. These guys do more than produce products that they know work-they know why they work. And of all the reasons to support their efforts, what's most important is this security that their knowledge and experience can offer you. After all, if there's one thing tuning your import can teach you, its that knowing how something works is more valuable than simply knowing that it does, and infinitely more so than worrying that it won't.