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What is a camshaft, exactly? Well, according to the dictionary, it is just a shaft that holds cams. So then, what is a cam? Let's again look at the dictionary for the exact description...
Cam : An eccentric or multiply curved wheel mounted on a rotating shaft, used to produce variable or reciprocating motion in another engaged or contacted part.
Ok, now that everyone knows what a cam is, let's define some of the typical terms associated with a cam.
- Lift is the amount that the valve gets opened. The lift at the valve is determined by the rocker arm, as it multiplies the lift of the cam lobe. For example, if a cam has a lift of 0.302", and your engine has 1.6 ratio rockers, the lift at the valve would be 0.302" x 1.6 = 0.483"
- Duration is the amount (in degrees) that the valve is above .050" of lift. Another form of this is Advertised Duration, which can vary depending on how the manufacturer decided to calculate it. Therefore, it is not recommended to use the Advertised Duration when comparing different camshafts.
- ICL is the intake centerline of the cam. This is the point where the intake valve reaches its maximum lift after top dead center.
- LSA is the lobe seperation angle, which is the amount of degrees between the peak of the intake lobe and the peak of the exhaust lobe. This helps determine the amount of overlap between the intake and exhaust.
Finally, a quick discussion on the lifters. There are 4 different types: hydraulic flat tappet, solid flat tappet, hydraulic roller, and solid roller. Since this article is for the Gen 3 camshaft, a hydraulic roller camshaft, it uses hydraulic roller lifters as the interface between the cam lobe and the pushrod. A hydraulic roller lifter is filled with oil so that it can expand and contract slightly to account for temperature changes inside the engine, and it utilizes a roller follower that rides along the cam lobe to reduce friction.
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