The camshaft is a very complex part of the engine and, as we have already discussed, is critical to getting the characteristics of the unit to suit the desired application.

Here we will simply look at the various items of terminology used to describe a camshafts profile.




The above diagram shows 2 important measures of a camshaft, these being the duration and valve overlap. The valve ramp is also included in this pic

Duration

The duration describes the period which the valve is open for from the moment it lifts off its seat until its sealed against its seat again. This is usualy quoted in CRANK shaft degrees (important to note this as its rarely quoted in camshaft degrees)

Ramp

This is the point where we start to accelerate a valve (open it)

Valve Overlap

Covered in Part 3, this is the point where both valves are open at the same time



Valve Lift

The theory behind this was covered in Part 2 and is described as the difference between the nose (peek lobe height) and base circle of the cam.

Seperation

This is the angle between the nose (peek lobe height) of the inlet and exhaust cam

Other parts of the cam

pm sent mark 

Thanks or another great article Mark. I have a question or two..

I haven't quite got my head around the profile of the cam lobe yet. But I presume in general terms that the ramp, flank and nose put together impose a half sine wave on the base circle?

The full sine wave would have a frequency of 'duration' x 2 and the amplitude would be 'lift' x 2?

If it isn't a half sine wave then Mr Fourier would say that the higher harmonics would tend to create valve bounce. Or have I lost the plot?

Thanks,
Jim