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A quick copy / past from another board discussing the same topic:
"Work is defined as Force * Distance. Say we have a valve spring with a seat pressure of 245 lbs. and installed height of 2". We also have a valve opening of 0.700 which gives an open spring pressure of 600 lbs. The work done is the area under the spring curve between the 2.000" installed height and the 1.300" open height. In this case about 296 in-lbs or about 25 ft-lbs.
Power is defined as the time rate of doing work, or Work/Time. At 7200 RPM the cam is spinning 3600 RPM, or 60 RPS, or 21600 cam degrees per second. For our cam, 264 @ 0.050, there are 66 cam degrees from 0.050 to max lift. Let's add another 24 degrees to from the base circle to max lift and call it 90 degrees.
This means it takes about 0.004 seconds to go from the lift ramp to max lift. So if we take our 25FtLb/.004sec = 6250 FtLb/Sec, and with 1 Hp=550 FtLb/sec, it takes 11.36Hp to open the valve at 7200 RPM. We can see that if the engine were only running at 3600 RPM, it would take twice as long to open the valve, so it would only take half the horsepower to open the valve.
Now that's just the power required to open the valve. It really doesn't answer the question about power consumed. That same energy stored in the spring at max lift has to go somewhere, so it delivers it to the cam on the back side. Theoretically, the net power should = zero in my mind. But there will be some loss by heat generated by the spring. Also, at higher RPM, as the cam tosses the lifter for a fraction of a second after max lift, the energy released by the spring doesn't return that power to the cam since the lifter isn't touching the lobe.
So I can see how there are some losses, but I just wonder how the claims of 20-30% came about. When you hear that stuff from several respected builders over the years, you just kinda take it at face value and don't question it."
Cheers , Pete.
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