I ran across an article that exposes the myth of high flow (pressure) pumps in most applications.
Engine builders...what's your theory?
More Flow?
More Pressure?
The Difference?
(Mods...let this thread "fly" and you will see the "high tech" nature of this topic)...

Thanks...

 

My concern is getting oil to the rod bearings, especially at high rpm.

Rod bearings are oiled from cross-drilled oil holes from the OD of the main bearing to the center of the main then diagonally out to the rod throw. Once the oil gets to the center of the main and started up to the rod, inertial force ("centrifugal force") does a good job forcing the oil to the rod bearing.

However to get oil to the center of the main, the oil pressure has to overcome the pressure (force/area) generated by that spinning column of oil from the OD of the main to the center. Here's the rub.

Because the force is proportional to the radius of the main and the square of the velocity, smaller mains make it easier to get the oil crammed down into the main at high rpm.

Trivia: When Smokey Yunick was racing Pontiacs in NASCAR he reduced the 3.25 dia mains of the 421 to 3.00 of the 389 in order to make them live at (then) high rpm of 6000+. He didn't tell many folks about this at the time. Pontiac knew they had trouble with oiling at 6000, but none of the production engines ran that high, and the overlap of the main and rod journals for strength was considered important.

Smokey's old "rule" of 10 psi per thousand rpm probably isn't all that far off. Priority Main Oiling on Bowtie and good aftermarket blocks seems to address this also: the closer to the pump the less the pressure loss.

I may be all wet (or oily) here. Comments are welcome.

My $.02

 

Best indicator of the condition of the pump and bearing clerances of the engine: idle speed oil pressure on a hot motor. If it' low here you've got problems of one sort or another. A stock volume pump should be able to maintain 20-25 PSI with 30W oil under these conditions. If you're down below about 15 PSI then the bearaings are loose or the pump is shot. A typical high volume replacement oil pump should be able to push 25-30 PSI.

Pressure when hot and revved up should be whatever the relief spring in the oil pump is set for. On a stock pump that's usually around 40 PSI. On a high pressure pump that's usually around 60 PSI or more. If it's significantly above the pump's set pressure, again, you've got problems- a restriction of some kind in the pump's relief valve, perhaps. Pressure should build quickly from idle speed (~20 PSI or whatever) to the pump's set point by the time you reach 2500 RPMs, and hold pretty much steady from that point up.

Loss of pressure at high RPMs is the result of inadequate oil control in the pan/pickup area in every case I've run into that problem.

Forget cold oil pressure- it's alway high and it's pretty much maningless. Pressures can vary wildly on a cold motor depending on the viscosity of the oil, whether it's synthetic or standard, etc.