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Old 09-13-2008, 01:47 PM
ScoTFrenzel ScoTFrenzel is offline
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Originally Posted by curtis73
No, but since the drag on the pump is exponential, (a function of the square of the speed and the pressure based on viscosity) and the pump spins the same speed as the engine (double the cam speed), try spinning that pump to 6000 with some cold 10w40 in the case. Now you've quadrupled the pressure, which (other factors excluded) has multiplied the drag on the pump by at least a factor of 16 - and that is simply from the oil pressure. That doesn't take into consideration the exponential increases in friction on the driveshaft, the drive gear on the cam, and the gerotor friction inside the pump.

People say the same thing about alternators because they spin so freely. Put a load on them and spin them to 5000 rpms and then see how freely they spin.

Oil pumps take considerable HP to run. Otherwise, why would manufacturers use a heat-treated chrome-moly 3/8" shaft to drive it?
Just a side note.
As for people spinning 6000 rpm on cold oil..... yes I have seen a few retards in action. LOL

4000 to 6000 rpm will NOT quadruple the pressure, nor the volume.
Oil pressure is controlled by a spring loaded pop off valve, which controls not only the pressure maximum but the overall volume pumped into the galleries.
Bypassing only reroutes the output to the input side of most of the pumps.

I know that SBC are notorious for poor oil pressure, hoping for at least 10 psi per thousand rpm, but most pumps have pressure springs set around 55 psi. maximum, which "should" be reached well before 5500 rpm. I have seen many that hit 55 psi at 3000 rpm with hot oil.
(Thos of you who have a Ford, yours probably idles with 55 psi hot )

IMO most shafts fatigue and twist off do to harmonic pulsations, not "oil pressure" that somehow? spikes to a million pounds and twists it off.

Dyno tests show that 60 amps draw on an alternator pulls 1 1/2 hp beyond the mechaincal load, which, I do not know how much power it takes to turn an alternator at 5000, do you?

JMO Thanks for the reply.

Last edited by ScoTFrenzel; 09-13-2008 at 01:59 PM.
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