Valvesprings are also a critical...
Valvesprings are also a critical component that should not be overlooked when building a performance engine...
Single- and Dual-Pattern Cams
As we learn more about camshafts, you find that the early cams tended to be relatively simple devices that have become increasingly complex, yet far better in terms of increasing engine performance. In the early days, intake and exhaust lobes were almost always the same. These were called single-pattern cams. But it didn't take the race-engine builders long to realize that often the engine's exhaust port was not as efficient as the intake and needed more duration to help scavenge all the exhaust gas out of the cylinder, especially at higher engine speeds. This demanded a longer-duration lobe on the exhaust side of the camshaft. These cams became known as dual-pattern cams.
Dual-pattern cams are now commonplace in even mild street engine camshafts. Ironically, as performance cylinder heads continue to improve, their exhaust ports are also achieving parity with the intake side of the heads, so the single pattern cam is again becoming popular, especially when combined with the better aftermarket small- and big-block cylinder heads.
...Weak valvesprings can allow...
...Weak valvesprings can allow the valves to bounce off their seats, robbing power with virtually no warning.
Cam Selection
Now that you have a general understanding of these concepts, you can employ them to help you in selecting your next camshaft. Of course, there are libraries full of additional material when it comes to camshafts, and we haven't even touched ideas such as adding higher-ratio rocker arms and how important valvesprings are to making power. Perhaps the most important point to make when getting into the cam selection process is that you need to focus on how the engine will be used. Camshafts have a major impact on where the torque curve begins and ends, and it seems like everyone always wants to use the biggest cam they can physically squeeze into the engine. This "bigger hammer" approach rarely is successful and usually results in a sluggish engine that doesn't make power anywhere. Taking a conservative approach to cam selection may not always make the most power, but it will offer an engine that can make respectable power over a broader rpm band, which is always useful for street engines expected to run well between idle and 6,500 rpm or more. In other words, that killer lumpy cam may sound nasty, but it rarely works well in a daily driven street machine.
This illustration reveals...
This illustration reveals how an eccentric is added to a simple circle to create a cam lobe. Note how the height of the lobe above the circumference of the circle represents total lift.
Conclusion
Armed with these basics of camshaft operation, you should be able to see why selecting a camshaft is not as easy as you might have thought, and that this simple-appearing device is actually incredibly complex set of mathematical models that have a headlock hold on the engine's power curve. The good news is that most street performance camshafts are relatively affordable and easy to exchange in the engine. So if you make a mistake, it is easy to rectify. But regardless of whether you're a racer or cruiser, a hard-core engine master or a first-time car crafter, there's a ton of information to learn so that you can be the cam guru on your block that everyone turns to for the correct information.