How exact do your calculations need to be?
Answer will vary between simulation and real world testing.
A new engine will have higher bearing friction due to high spots present on bearing surfaces leading to surface contact and therefore boundary/mixed lubrication. For the first while, figures will drop, and then level off once everything is run in.
This is also the case for any follower mechanism.
Keep in mind that the opposite is true with reference to piston rings, and bore sealing. This will have a direct effect on cylinder pressures.
Depending on what you want to test, and how accurate you want to be, you could do a bench test. Rotate cam and measure load.
End result will depend on how much stuff you add to the test rig, what temperature its at, what the oil temperature is, if you have springs fitted, etc. These will have to be taken into account, as will cam to follower friction loads.
Then you have cylinder pressure, and the force it exerts on the exhaust valve at the point where the valve cracks it open.
Timing belt load is not to be ignored either, journals nearest the timing belt pulley will show increased loads. Same is true if its a twin cam, and one cam drives the other.
Dont forget any sundry devices also driven off the cam via lobes, or gears.
There is software out there for calculating theoretical values, I have no doubt that it is expensive, and totally useless if you dont know what Inputs to clock in.
I know Ricardo Uk did or still does case studies on all the above. Im not sure if they do software packages also, but I remember reading studies years on on engine friction that they had carried out, so perhaps dig through their archives. I do remember they always carried out actual bench tests to verify the calculations.
As mentioned by Dicer, lot of variables...and not a ten minute calculation.
Brian,
