Jump to content

Cam Relationships


Recommended Posts

Time to add something to the cam forums. Y'all have heard the terms, here's the math that defines the cam parameters. First, the definitions.


Overlap: period in crank degrees when both intake and exhaust valves are off the seat.

Duration: period in crank degrees when one valve is off the seat (seat to seat duration) or at a given lift value (0.050" typical).

LCA: lobe centerline angle or the angle in crank degrees between the peak of the intake lobe and the peak of the exhaust lobe. Note that in a single cam (overhead or in block) application the LCA is ground into the cam, in a dual overhead cam application the LCA can be altered using adjustable cam gears. Either way the math still applies.


Duration = (overlap/2 + LCA)*2

Overlap = (duration/2 - LCA)*2

LCA = (duration - overlap)/2


Point being if someone gives you two of the values you can calculate the third, they are all inter-related. Put another way you can't have big duration and overlap without having big LCA, it is forced into the design.


From the FSM, stock slipper lobe cam specs: Overlap 45 degrees, duration 264 degrees, the LCA must then be (264 - 45)/2 or 109.5 degrees.

Link to comment
Share on other sites


  • Create New...