Regulating high-RPM oil pressure

[richie,uk]

Couple of things I can add to this that may help, 1st i have tested pressure stock oil cooler to 120psi, at that level some started to fail others were ok, but at 100psi none failed, this was most likely that they were all older used coolers and some may have had a hard life so failed sooner!!! But its not going to fail at 65psi unless its already totally fcuked

I set my dry sump pressure relief valve at 80psi on both drag and road race engines, I have logged it a lot and it maxes out at 78psi based on the pressure sensor i use. It is usually at that psi by about 5000rpm and stays same to over 9000rpm.

One of the benefits of a dry sump set up it running an oil heater in the tank, this solves so many potential problems like your worry about oil bypassing stock cooler plunger I have a heater in all of my dry sump set ups

cheers Richie

[Crawdad]

Thanks, FJ. It would be great to have Paul around to really get into this stuff, even if it has little practical upshot. What you say makes sense: compared to water, oil will maintain a greater gradient of temperature across layers in laminar flow, because it doesn't conduct heat as well between its own layers. So if you had oil in laminar flow along a pipe, reading the temp on the surface of the pipe would give you a false low reading (if what you really want to know is the average temp). Presumably the flow is laminar along a long oil gallery, and in the oil wedge of a plain bearing at speed. But as soon as it gets released into the valve cover or sump, it all gets mixed up. Reading the temp there should give a good indication of how hot the oil is.

[FJCamper]

Hi Richie,

We also have a tank heater (120vac blanket-wrap type) in our Bug. The tank is right beside the driver, passenger side. We do race in some cold weather. It's funny on some frigid mornings to see a crewman or driver huddled in the driver's seat, with the access door open on the oil tank containment enclosure, warming their hands over the rising heat.

Our Ghia races vintage, think Goodwood, under more posh circumstances, and has crew minions to warm it up

[Bruce2]

Putting the practicalities of VW engines aside for a moment, there's an interesting bit of physics here...

"When the oil is under pressure, it has potential energy." It would if it were a compressible fluid (like air). For such a fluid, the amount of energy stored can be expressed simply: PV=nRT where P is pressure, V is volume, n is the number of gas molecules, R is a constant and T is temperature. But because oil (like water) is incompressible, putting it under pressure doesn't do any "work" on the oil itself. It can TRANSMIT force (for example, run a hydraulic motor), but it hasn't stored any energy. In an air conditioner, by contrast, the "working fluid" is a gas (freon) that gets compressed over here, and expands over there, moving heat energy from one location to another through its compression and expansion. When it's compressed, it is storing potential energy. You could use that energy to do all sorts of work, for example to shoot a projectile.

Based on this logic, I'm starting to doubt the internet wisdom I cited earlier, about the oil getting heated by passing through a restrictive hole. IF that is true, it would be due to viscous friction, not compression.

gasses and liquids act the same as far as energy transmission. Your example of the thermodynamics of an air conditioner is exactly applicable to the engine oil.
Compressibility is irrelevant.
Any liquid under pressure has stored potential energy. When the liquid gets pressurized, energy has to be put into it. When that liquid does work causing the pressure to drop in the process, energy is being released by it. But not all of the potential energy can be extracted to do work (like drive a hydraulic motor). The remaining potential energy that didn't do work and was vented to the sump will be instantly converted to heat (in the liquid).

[Tony Z]

My NEW worry (I worry a lot - worry twice, build once) is about the other valve – the relief valve at the pulley end – which controls the pressure at which oil gets sent to the cooler. Using pressure as a proxy for temperature isn't ideal, especially if using modern, light-viscosity synthetic oil, which will trick the system into thinking the oil is warm when it isn't. Making matters worse, the stock-strength spring doesn't seem to be available anywhere, only the "pressure boost" springs that have the effect of making oil go to your cooler at a lower temperature (compared to a stock spring). For a daily driver, that seems like a really bad idea, especially if you've got a couple gallons of oil to heat up. The obvious solution is to use a real thermostat. But I'm clinging to the idea of using the stock cooler, rather than adding yet more plumbing and expense. If my oil isn't getting up to temp, I'll have to rethink.

I'm going through this thread and have to ask a few questions and point out something:
above, in your quote, you say the pressure boost springs make the oil cooler. Not quite. The pulley side relief valve closes the oil path to the cooler when pressure is high (cold oil) and opens it when oil is warm. Increasing the pressure that this happens at only serves to cook your oil. Hense why bigger oil pumps dont actually cool your oil more unless you add external coolers for the oil to go through.

My question is: Why do you want more oil pressure? Without re-reading your posts, I'm remembering you talking about going from 60psi to 80psi on the relief. Again, why?
On hydrodynamic bearings (plain bearings like we use in a bug engine), the crank isnt supported (lifted) off from the bearing by the oil pressure. The oil pressure serves to get the oil to the bearing and then once its there, the rotational speed of the crank is what forces it between then bearing and the crank. The supply pressure has very little to do with this hydrodynamic wedge of oil, its all in the speed difference between the two surfaces.
Yes, the pressure gets the oil to where it is needed and higher oil pressure will supply a little more oil, but there is only a certain amount that will be able to flow through each bearing unless you reduce the viscosity.
friction head = (4x flv^2)/2gd
f = friction coefficient, l = length of system, v = velocity, g = gravity, d = diameter of pipe
note that velocity is squared in this formula
so going from 60 to 80psi = (8/6)^2 = 1.78, which means that your pressure increase leads to 78% more friction losses on the system - or, 78% more power needed to drive the oil pump = more engine losses and more heat pushed into the oil.
Again, why would you want this when you are getting all the oil to all the points that you need it and the velocity of the parts is doing the rest.

For reference, I run 15W40 with 26mm oil pumps on all my engines except my 2332 street beast, which I use 5W30 with a blocked off stock cooler and a single smallish external cooler and a 26mm oil pump.

[Bruce.m]

Just to be pedantic here… & not disagreeing with any of your points…

The oil pressure relief valve closes the oil cooler bypass, not the path to the cooler. If the oil pressure on the input side of the oil cooler goes too high, the valve opens allowing the oil to bypass the cooler (the path to the cooler is never closed but the oil will take the easier path). By increasing the spring pressure you force oil through the cooler, in theory when the oil is cooler & thicker as it is harder to open the cooler bypass.

However, if you fit an oversized pump and use high
Oil weight, then it may mean that even when the oil is very hot, the oil pressure before the cooler could be high enough to force open the bypass valve & skip the cooler.

[Druck1]

Question related to the original post. I too am going dry sump with CB Performance pump
Would a Gene Berg style pressure relief cover provide the same benefit as an external pressure relief valve that dumps back to the tank?

[richie,uk]

Question related to the original post. I too am going dry sump with CB Performance pump
Would a Gene Berg style pressure relief cover provide the same benefit as an external pressure relief valve that dumps back to the tank?

If you are using CB pump as supplied then the outlet from pump is just the return to tank, its not a pressure line so adding pressure relief to it will do nothing at all. The CB pump uses the factory pressure relief valves inside the case only

cheers Richie

[Ol'fogasaurus]

https://www.vehiclescene.com/too-much-o ... ar-engine/

Other examples of too much oil pressure.

Lee