Quote:
Originally Posted by Frank Lee
one with 5% valvetrain losses, one with 19%. What's the diff?
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Frank ,
Apart from the obvious RPM differences for the two engines mentioned (1300 for the Perkins and 2500 for the Mercedes) I a guessing the detail design differences (finger roller valve operation versus bucket tappet operation etc) may account for the rest.
The comments about the actual values of the valve springs themselves being basically a zero sum item is essentially correct as Metro MPG stated above.
The force needed to compress the valve spring is returned as the compressed spring releases the energy stored in it.
There is a small amount of internal friction within the steel and this is released as heat.
The differences in spring pressure add to the friction component of the engine by the added pressures they apply to the items they contact like camshaft bearings , rocker bearings and pushrod contact points.
Cheers , Pete.