Let’s take a look at what makes this simple eccentric device so powerful.Lift We’ll start with the easiest concept involved with the camshaft–lift.When installing a camshaft in an engine, performance engine builders and the blueprinting process demand that you measure or “degree” the camshaft to ensure that it is installed where the engine builder desires.
For most street-type cams, this will be roughly between 0.275 and 0.450 inch. But we don’t generate this lift all at once–it’s created by gradually moving the tappet from the base circle to maximum lobe lift. Duration Ideally, you could slam a valve open, hold it open, and then slam it closed, and many drag race camshafts attempt to perform this feat, but this harsh action is incredibly abusive on valvetrain parts, especially valves and springs.
To make these parts live over hundreds of thousands of miles, the cam lobe lift curve must be gentler.
A cam lobe starts off from a simple circle, called the base circle of the cam.
From that circle, the designer creates additional lift using a ramp so that as the circle rotates, it converts rotation into a linear or vertical motion by using a follower or tappet.
Imagine looking at a lobe with a vertical line running right down the middle as viewed from the end.
This line would represent the centerline of the lobe.
Conversely, a very short duration camshaft opens the intake valve later and closes it sooner, reducing the potential for high-rpm horsepower but increasing torque at a lower engine speed.
Intake Centerline Now that you have lift and duration mastered, we can move on to more of the measurement values in camshaft design.
The easiest way to measure the amount of time the lobe is creating lift is with degrees of duration.
A long time ago, our cam-building forefathers decided to use crankshaft degrees to measure cam lobe duration.
But this created confusion because all the different cam companies measured the beginning of the lift curve at different points a few thousandths of an inch above the cam’s base circle.