A cam profile is the specific geometric shape of a camshaft lobe. This shape dictates the timing and physical movement of the valvetrain. The performance characteristics of an engine are primarily defined by three key measurements: cam lift, duration, and overlap.

Key Measurements#

Cam Lift#

Cam lift is the maximum distance the valve is pushed open from its seated position. This is determined by the difference between the base circle of the camshaft and the peak of the lobe. Increased lift allows for a greater volume of air and fuel to enter the combustion chamber, provided the cylinder head flow capacity supports the increase.

Cam Duration#

Duration refers to the number of degrees of crankshaft rotation during which the valve remains open. It is typically measured at a specific lift point (e.g., 0.050" lift) to provide a standardized comparison between different camshaft profiles. Longer duration keeps the valves open for a larger portion of the engine cycle, which is generally beneficial for high-RPM power production.

Cam Overlap#

Overlap is the period during which both the intake and exhaust valves are open simultaneously. This occurs at the end of the exhaust stroke and the beginning of the intake stroke.

Note

Proper overlap tuning is critical for scavenging, where the exiting exhaust gases help pull the fresh intake charge into the cylinder. Excessive overlap can lead to poor idle quality and reduced low-end torque.

Summary of Effects#