Urban Legends oil pumps.

[OnThe7ThDayFord]

I get irate when people talk about HV oil pumps being bad because there is too much flow and it will pump too much oil to the top end starving the sump.

Pressure and engine clearances determine the flow. So for a brand new engine with both oil pumps putting out 80psi the flow is exaclty the same.

In an engine with worn bearings or higher clearances the standard pump will not be able to maintain 80psi because it doesn’t have the size to flow more at that pressure. The HV can keep up and will maintain the 80psi even though more oil is escaping past the bearings ie higher flow.

A high volume pump will be able to maintain more pressure on a higher mileage or higher clearance engine than a standard pump. That’s a good thing.

Eveyone of my truck with high millage has always gotin a new high end oil pump. I do not go by the stock gauges I run after markts (Wife hate it) 9 out of 10 time there is 10 to 15 psi difference between the two and you can argue with what the gauges say.

now think it thru,
(1)pressure is the resistance to oil flow
(2) the high voluum pump can push about 25% more oil
(3) the oil pump bye-pass circuit limits the max pressure in either size pump to about 65lbs-75 lbs MAXIMUM before it BYE-PASSES all additional oil voluum
(4) the engine can accept and use only the max flow voluum that the engine passages can flow at the max pressure the pump provides , at any point less than max pressure the passages can flow only what the pressure and voluum provided by the pump supplies
(5)if the bearing clearances can flow more than the pump provides in voluum and pressure at any rpm level the film of cooling oil that provides a cushion between the bearing surfaces are at risk of not being supported and seperated by that cushion of oil
(6) now since the sweep voluum is greater with the high voluum pump it will reach that bye-pass circuits max pressure at about 25% lower rpms and supply a POTENTIALLY higher voluum of oil to the supply passages/bearings
(7)SO… all a high voluum pump does is provide the maximum oil flow the engine can use up to the max pressure allowed by the bye-pass circuit at a 25% lower rpm level if the system can reach max pressure, but it also supplies 25% more oil at every rpm level below that point to provide additional cooling and protection for the engine. and if the engine can flow more than the stock pump can provide the high voluum pump helps fill the need faster
(8)oil flow through the bearing clearances INCREASES at a faster rate as the rpms increase
(9) in most engines the oil flow can be provided by the stock pump IF the clearances are close to stock AND THE RPM LEVELS ARE KEPT IN ABOUT THE idle-6000rpm range but if rpm levels exceed ABOUT 6000rpm,or if bearing loads greatly exceed the stock hp levels, or the clearances are greater than stock, the high volume pump is a good idea , simply because it potentially provides that extra volume of oil.

any less than about a 1/4″ tends to restrict oil flow into the pick-up on many oil pump pick-up pan combo designs and more than about 3/8″ to about 1/2 MAX tends to allow air to be sucked under some hard brakeing or accelleration with some pan and pick up designs so a 3/8″-1/2″ pick-up to pan floor clearance is what I tend to try for, Ive seen numerious cases where a high voluum pump was installed without checking the clearances (and of course the pick-up moved closer to the oil pan floor simply because the oil pump itself is longer and the pick ups deeper in the pan if its reused from the old pump)and the engine SEEMED to run out of oil pressure almost instantly on accelleration, (im sure this is what leads to the myth of pumping the pan dry, but simply swapping pick-ups and verifying the pan floor to pick-up clearances cured the lack of oil flow into the pump and restriction that was the true cause of the low oil pressure condition.

remember the high voluum pumps have a deeper body to fit the longer impeller gears. this places the oil pump pickup closer to the oil pan floor if no other changes are made when swapping to a high voluum pump from the standard pump and can restrict oil flow into the pump

if you choose to install a high volume oil pump you should SERIOUSLY consider the fact that the pump is only a small part of the whole oil system,(which includes a high volume BAFFLED oil pan (7qts or more is ideal) and a windage screen, which is necessary to quickly return that extra oil to the sump, and doing the distributor mod is a big help, as it prevents any potential for cam/gear wear (something already almost non-existent with synthetic oil and the proper distributor gear material.)

the bye-pass spring only limits the pressure at which the bye-pass OPENS thus it only effects the upper pressure limit and has NOTHING to do with oil pressures or flow BELOW that level

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[spelunkerd]

That’s a thoughtful essay with a good review of the theory. Great read.

[Author]

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