how much oil pressure is too much?

[Kevin Johnson]

David clearly understands the issue; the problem is simply a transposition in the sentence. Spoonerisms are a comparable example that processing of information in the mind is not linear: the fit hit the shan and so forth. Another example would be in the German language where verbs are sometimes stacked up at the end of a sentence or clause.

...As bearing clearance increases, the flow orifice is increased allowing a greater outflow flow of bearing oil but with a resulting drop in oil pressure. Now it is necessary to increase volume flow to maintain oil pressure.

As Bill points out, with a positive displacement pump a simple increase in rpm will suffice and delay (or even eliminate) the onset of relief valve actuation.



~~~~~~~~~~~~~~~~~

...As bearing clearance increases, the flow orifice is increased allowing a greater outflow flow of bearing oil but with a resulting drop in oil pressure. Now it is necessary to increase oil pressure to maintain volume flow.
.

???
Because it is a positive displacement design moving an essentially incompressible fluid, if the pump is operating below the relief spring cracking pressure, the volume should be dependent only on RPM and to a slight extent internal leakage. Once the relief valve comes into play the overall flow restriction will reduce net delivery volume at that RPM (as some flow is recycled internally) and increase pressure (although at a lesser rate than if un-relieved) as more backpressure forces the valve to open further, which requires further relief spring compression and thus higher relief pressure. (e.g., if the relief valve piston was say 1" diameter, there would be far less output pressure variation, as very little spring force increase wold occur with the slight piston travel necessary to dump the excess flow)

[Kevin Johnson]

A HV pump is good for higher pressure at idle and very low rpm, but a lot of people (me including) are having issues with oil pressure dropping of at high rpm. It seems to be specifically related to the HV pump.

Association is not causation.

[Kevin Johnson]

To expand on Bill's answer (1.) the pumping exchange patterns from bay to bay on a straight six are tortured. The center pair rise and fall together making a very imbalanced strong central pulse, for starters. If the crankcase is at atmospheric pressure or higher, this could be the source of the problem as well. This would be somewhat related to the problem with stroker engines pushing the surface of the oil up the side of the pan in the reservoir allowing vortexing.

Is the sump reservoir well shielded from pumping exchange airflow? I am assuming you mean a wetsump. In the RB26DETT, (going from memory) Nissan used three different levels of trays.

...Upon recently examining the oil pressure traces from a six cylinder turbo motor, I was rather suprised to see oil pressure fluctuations in excess of 20psi (65-85psi), at very similar rpms (4800-4900). The fluctuation occured at 1.45Hz and varied in amplitude with increasing rpms. And this was from an engine running on the dyno.

Bill, can you offer any suggestions as to the cause and cure for fluctuating oil pressure?

The first two that come to mind are 1. Some kind of vortex/cavitation issue in the pick up that causes periodic air/vapor embolisms; the resulting 'packets' of compressible fluid could cause such pressure fluctuations. 2. Resonance of the relief valve poppet/spring system, excited by gear tooth-induced pressure pulsations. One more would be an air pocket in the system or a 'springy' section of oil passage that could resonate when excited at the correct frequency by one of the aforementioned mechanisms.

[Belgian1979]

A HV pump is good for higher pressure at idle and very low rpm, but a lot of people (me including) are having issues with oil pressure dropping of at high rpm. It seems to be specifically related to the HV pump.

Association is not causation.

No, but it's reason enough to look further into the reasons why this may happen on so many different setups with apparently the same result. Too many people complaining about the same effect to be just coincidence.

[Belgian1979]

...Upon recently examining the oil pressure traces from a six cylinder turbo motor, I was rather suprised to see oil pressure fluctuations in excess of 20psi (65-85psi), at very similar rpms (4800-4900). The fluctuation occured at 1.45Hz and varied in amplitude with increasing rpms. And this was from an engine running on the dyno.

Bill, can you offer any suggestions as to the cause and cure for fluctuating oil pressure?

The first two that come to mind are 1. Some kind of vortex/cavitation issue in the pick up that causes periodic air/vapor embolisms; the resulting 'packets' of compressible fluid could cause such pressure fluctuations. 2. Resonance of the relief valve poppet/spring system, excited by gear tooth-induced pressure pulsations. One more would be an air pocket in the system or a 'springy' section of oil passage that could resonate when excited at the correct frequency by one of the aforementioned mechanisms.

What is a typical pressure drop associated with the oil under pressure flowing through the bypass valve and through the opening between the bypass channel and inlet channel of the pump ?

[MadBill]

...
What is a typical pressure drop associated with the oil under pressure flowing through the bypass valve and through the opening between the bypass channel and inlet channel of the pump ?

I've never seen such data (and I'm trying to think why it would be of concern), but excluding the delta across the valve itself (say 40-60# plus, depending on the setup and on how far downstream the gauge is tapped in) it would depend on the pump size, RPM, viscosity, temperature, percent opening of the valve, etc. I would suppose it's pretty small, likely just a few psi, since the path is so short and there is no downside to using a generous diameter...

[Kevin Johnson]

A HV pump is good for higher pressure at idle and very low rpm, but a lot of people (me including) are having issues with oil pressure dropping of at high rpm. It seems to be specifically related to the HV pump.

Association is not causation.

No, but it's reason enough to look further into the reasons why this may happen on so many different setups with apparently the same result. Too many people complaining about the same effect to be just coincidence.

There is a stronger correlation with too high of oil level regardless of pump type. I agree though that investigation is worthwhile.

[Nick Campagna]

Electric driven pump to maintain a predetermined oil pressure vs rpm ?
Feasible ? Available ?

[Belgian1979]

...
What is a typical pressure drop associated with the oil under pressure flowing through the bypass valve and through the opening between the bypass channel and inlet channel of the pump ?

I've never seen such data (and I'm trying to think why it would be of concern), but excluding the delta across the valve itself (say 40-60# plus, depending on the setup and on how far downstream the gauge is tapped in) it would depend on the pump size, RPM, viscosity, temperature, percent opening of the valve, etc. I would suppose it's pretty small, likely just a few psi, since the path is so short and there is no downside to using a generous diameter...

Well Schumacher seems to be of the opinion that rerouting the bypass back to the intake causes problems. When I talked at length with them about their pumps that route the bypass oil back to the pan, they specifically seem to suggest that the oil would back up in the inlet path to the pickup for one (causing inlet restriction). When I disassembled my HV pump, I noticed that the orifice going from the bypass to the inlet was a lot smaller than the bore of the bypass. It's a fact that anytime a high pressure fluid has to pass a smaller orifice it would create a pressure drop and bubbles...something that could potentially aggravate a cavitation issue.

Other like Carl here seem to use a through drilled hole (one exiting on the pan side) in effect reducing the amount of oil that would have to pass through the internal orifice with good effect.

All those how complained about the HV pump dropping off, seem to report it dropping of at a similar rpm. Coincidence ? Personally I don't think so.

[Belgian1979]

There is a stronger correlation with too high of oil level regardless of pump type. I agree though that investigation is worthwhile.

Car is not in. External bypass is by now.

As a matter of a fact, reading through 1000's of threads all over different forums and the different things people told they tried + my own testing learned me something : it's not application specific, it's not pan specific, it's not oil level specific, it's not bafflesystem specific, it's not cooler specific, it's not external filter specific, etc... it's pump specific and it's rpm specific though + the effect are somewhat affected by viscosity. I could have tried 5W20 but I'm too chicken because of possible adverse effects on oil wedge strength.

[Kevin Johnson]

There is a stronger correlation with too high of oil level regardless of pump type. I agree though that investigation is worthwhile.

Car is not in. External bypass is by now.

As a matter of a fact, reading through 1000's of threads all over different forums and the different things people told they tried + my own testing learned me something : it's not application specific, it's not pan specific, it's not oil level specific, it's not bafflesystem specific, it's not cooler specific, it's not external filter specific, etc... it's pump specific and it's rpm specific though + the effect are somewhat affected by viscosity. I could have tried 5W20 but I'm too chicken because of possible adverse effects on oil wedge strength.

I hope this works and you are able to finally enjoy driving your car once again. Now you just need to erect a force field around it against stupid drivers.

[af2]

af2, I don't see what my post has to do with pan or stroke. rally mentioned the z-28 pump is HV. I questioned that.

It has a lot to do with the pan and stroke.
The Z28 pump is standard volume from what I have seen. Your question is valid because Chevrolet never used a HV pump...

[engineguyBill]

There is a stronger correlation with too high of oil level regardless of pump type. I agree though that investigation is worthwhile.

I could have tried 5W20 but I'm too chicken because of possible adverse effects on oil wedge strength.[/quote


Actually the oil wedge strength (or lack of strength) is not affected by oil viscosity - as long as vertical oil clearance between the bearing shells and crankshaft journals are not excessive.

[robert1]

af2, I don't see what my post has to do with pan or stroke. rally mentioned the z-28 pump is HV. I questioned that.

It has a lot to do with the pan and stroke.
The Z28 pump is standard volume from what I have seen. Your question is valid because Chevrolet never used a HV pump...

Wrong Chevrolet uses a high volume pump in their crate engines, at least the ones I've looked at.

[nhrastocker]

Every factory oil pump I removed in my early days from either a Z-28 (302) or LT-1 (350) engine, was a high pressure oil pump.