I further explained my viewpoint to clarify my statements as this discussion unfolded, but seems you're not quite following or grasping the details. This whole side discussion came up when I pointed out that a few more PSI of dP across an oil filter due to fewer or smaller base plate and/or center tube holes (within reason - very closed off louvers is another side discussion) won't really matter to a PD pump. I stand by that statement. Your definition of "matter" and my definition seem to be different. Tell me when it would "matter" to you. The PD pump is still going to supply the same basic oil flow volume per RPM when the total back pressure on the pump has only increased by 1-2 PSI. Do you really think that adding 1-2 PSI of dP to the oiling system is going to make any real difference to a healthy PD pump? Is it going to suddenly starve the engine of oil flow and blow-up the engine? Do you think you could actually measure the difference in total flow to the oiling system due to adding 1-2 PSI of dP accurately with instrumentation? I say no you couldn't because it's a very small impact on oil volume from the pump due to the difference in slip caused by 1-2 more PSI of back pressure on the pump (all other factors held constant of course). That is my "the difference will be negligible" clarification, and I already tried to make that clear before this post as the discussion progressed.To be clear, I'm calling you on an upfront blanket statement that you made.
I think we've established, it does matter, even if not an order of magnitude, or twofold, etc. Why not say something like, "it will matter little" or "the difference will be negligable" rather than standing beside a blanket and misleading statement about oft misunderstood PD pumps. Centrifugal pumps and gear pumps doing work on incompressible fluids both have curves that are...curves.
Again, look at what the difference is to the overall dP of the entire oiling system and to the back pressrue on the pump when different oil filters are used. It's only a few PSI of dP difference. I ran 4 different oil filter brands on my Z06 and collected the same oil pressure vs RPM data with oil temperature at the same 200F, and there was no difference seen in the curve that I showed in post #17. I'm sure there must have been at least 1-2 PSI of dP difference across the filter between them, but I saw zero impact on the oil pump's performance. If any of those oil filters effected the pump's performance in anymore than just a "miniscule" or "negligible" manner, I would have seen it with the tests. That engine RPM vs oil pressure curve would have changed, but it didn't.We have established that pump slip is a function of backpressure, which is additive for all components in the system, including the filter. The pump curve graph I shared shows this. Backpressure and viscosity determine slip. So yes, your curve shows slip increasing as pressure increases, but your data log graph is not one of pump flow vs engine rpm. It is pressure vs rpm, which is a related but different. To call the two the same would be making a big assumption about the fluid dynamic behavior of every oiling passage/component in the engine at various flow/pressure states. I don't remember many linear relationships in fluid dynamics.
Please show me with any oil pump performance curve for a typical automotive oil pump, what the output volume flow difference would be with only 1-2 PSI more or less of back pressure on the pump output.
I said pump slip increases as the back pressure on the outlet of the pump increases, and also as the oil viscosity decreases. Yes, pump slip is present at all RPM, but the total volume that "slips past the pump" is less at lower RPM than at higher RPM because the back pressure on the pump increases with RPM. I've said nothing contrary to that. If you want to make the statement that "the % of slip volume relative to the total pump output volume is smaller at higher PRM", then knock yourself out. But the fact remains that there is more oil volume slipping past the pump as the RPM increases and the oil back pressure on the pump outlet increases. I'm just looking at the volume slipping by, and not comparing that volume "relative" to the overall output volume of the pump. That's the difference going on here.You recognized it. Then you tried to further proove your point and got it backwards. Pump slip is present at all RPM. It increases with pressure but becomes smaller relative the pump output at higher flow (RPM.) PD pumps are used across the world at constant RPM but variable output flow and/or pressure.
See my response above. Sure, but again as the RPM increases so does the back pressure, which means slip does increase with RPM indirectly - so it certainly is a function of RPM. My statement is still true that the pump slip increases with RPM, regardless of what the root cause is.Again, pump slip is not a function of RPM. It is a function of backpressure.
Yeah, slip increases with higher RPM, which causes higher oil pressure in an engine oiling system ... I've never claimed anyting otherwise. Each one of the data points in my experiment was at a constant engine RPM and at a constant oil temperature. How do you think I could plot data of engine RPM vs oil pressure without getting those measurments at the data points I've shown? Oil temperature was also constant. The graph is pretty self explanitory.In your experiment, backpressure and RPM are not held independent. Slip increases at higher pressure. RPM was the innocent bystander, a variable your test setup did not allow to be held constant.
Can you please explain to me what the graph would look like if the oil pump had zero slip?
Last edited: