It's appropriate, we think, that a camshaft has lobes, since this relatively simple device is so often called the brains of an engine. And indeed, a camshaft does direct several engine functions in a brain like manner, controlling when an engine's valves open, how long they stay open, and when they shut-thus determining how much power that engine makes. On the other hand, the arrangement of the cam's lobes gives an engine its personality, influencing what type of power it will make and where it will come on in the rpm range. The camshaft may be the brain of an internal combustion powerplant, but for performance enthusiasts, it's also the heart and soul, giving our engines their very character. When properly matched to the other components to meet a specific goal, a camshaft can create an engine that's a dream to live with. A poorly chosen cam, on the other hand, can create an ill-tempered, underperforming beast.
Notice that when we talk about the right cam, we're talking about the right cam for your combination. A multitude of variables must be taken into account when selecting a camshaft. Engine displacement is a biggie, so to speak, but so is engine compression. "You have to have a suitable compression ratio for what you're doing," says Crane Cams' Chase Knight. Too little compression ratio-or too much duration-can lead to a drop in cylinder pressure and a corresponding drop in power. Too much compression- or too little duration-can create too much cylinder pressure, leading to detonation. Both are bad, and good reasons to follow the cam maker's compression ratio guidelines. Other factors to account for include the type of cylinder heads, the intake manifold design, and the carb size. Then again, you can't drive an engine by itself, which brings in a whole new group of variables: car weight, transmission type, torque converter stall speed if running an automatic, and rearend ratio. It's a lot to consider.
But the biggest considerations are honesty about your purposes and the setting of realistic goals. "When it comes to what camshaft you need, you have to ask, 'What are you trying to make?'" opines Comp's Billy Godbold. "With really excellent cars, I guarantee you, there was a plan that was followed." So what's your plan, and is it reasonable? Lots of high-rpm horsepower sounds good, but how often will you actually rev the engine to 7,000 rpm to get that power? Are you planning to go racing on a regular basis, or do you actually fall more on the street side of the street/strip equation? Possibly you want a ride that can handle the Hot Rod Power Tour...or do you really just need a little extra something in a daily driver?
Whatever your goals are, be honest with yourself-if you're not, chances are you're not gonna be pleased once that new 'stick is in place. "Guys pick a cam, we advise against it, they end up calling back," says Knight, the implication being that the customers aren't happy when they make that second phone call. In the end, it's all about creating a power curve you can use, with power happening where you actually drive the car. "To me, torque is what makes everything fun, especially when you can smoke the tires at 3,000 rpm," says Knight. It's a good point, and harder to do if your peak torque happens at 5,000 rpm. On the other hand, if you are going racing, and can actually use high-rpm power, cam accordingly. "Buy a cam for the car you have, and not for the car you want," says Godbold, a piece of wisdom echoed by all our experts.
Lobe Separation Angle Effects...
Lobe Separation Angle Effects
Increased low-rpm torque
Reduced idle quality
Increased cranking compression
Decreased piston-to-valve clearance
Wide LSA Reduced overlap Improved...
Improved top-end power
Improved idle quality
Reduced cranking compression
Increased piston-to-valve clearance