Kansas, would you say... - Saab Sonett Bulletin Board - Saabnet.com
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Kansas, would you say...
Posted by spiv (more from spiv) on Tue, 25 Sep 2007 19:58:39
In Reply to: Re: Oil Pump Choice, kansas, Tue, 25 Sep 2007 17:52:21
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...that if you increase the total surface area of the oil system, a higher-volume pump would be useful to maintain the same pressure?
The specific example of which I'm thinking is adding an oil cooler. This is a very common mod on high-performance engines, and I suspect this may be why race engines typically use higher-volume pumps.
My thinking is that if the total surface area of all the little oil passages inside the engine is X square inches, and the pump moves enough volume to pressurize the system to Y pounds, then the average pressure within the system is going to be Y/X pounds per square inch. (European readers feel free to substitute metric measurements.)
So, if you were to add more oil plumbing that would increase the total surface area to 2X square inches, with the same pump, then your average pressure would be Y/2X, or half what it was originally. To get back to the original pressure, you'd need to move twice the volume, correct?
The shop manual says the oil pump's relief valve opens at 47 - 55 psi, so that sets an upper limit on the system pressure (unless you tinker with the relief valve.) My older, high-mileage V4 generally shows about 40 psi at highway speeds when fully warmed up, but I've seen it get up near 50 when the car is first started on cold days. This suggests to me that the stock pump has enough capacity to fully pressurize a stock engine, but maybe an oil system enlarged with a cooloer or other add-ons would need more volume to keep pressure in the desirable range...?
posted by 72.213.24...
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