But we're not interested in oil qualities here, we're interested in steering you towards true engine operation. Steer you away from your Sommerfeld Blues wherein you want to deal with the variables as much as you want to steer me towards your newer PD pumper studies, could that be?
But the oil quality/formulation does play a role in how the HTHS viscosity behaves. And that also ties into the Sommerfeld number (S), which then determines the instantaneous operating MOFT. The bearing physical design (l/d ratio), RPM and loads of course also play a role.
Go read from equation (3) on page 49, and look at Figure 4 on page 50 in the link below. Figure 4 says the MOFT is always increasing with a larger Sommerfeld number, and even says that the multi-grade oil gave better MOFT at higher S numbers. My whole argument is that the MOFT will increase with increased oil viscosity (meaning a higher HTHS at whatever shear rate) with higher RPM if all other factors are held constant. You are only finding information where certain oil formulations have weak HTHS viscosity which hurts the building of MOFT at high RPM in a journal bearing.
The point is, the Sommerfeld relationship is valid, and the real question is how does a specific oil formulation behave in a specific engine. The guys doing those tests might not have even been able to accurately measure HTHS viscosity above 1M/s^2 shear rate in the lab and therefore had a hard time getting a good Sommerfeld correlation. With all other variables that effect MOFT held constant, an oil with higher HTHS viscosity (the viscosity inside the bearing at whatever actual shear rate) is going to result in higher MOFT than an oil with less HTHS viscosity at that same shear rate. Do you actually believe Sommerfeld's work? It's not a stretch to see that if the oil HTHS viscosity suffers inside the bearing due to whatever factors, then the MOFT will also suffer. I doubt you are going to find any study that says
with all Sommerfeld factors held constant except the actual viscosity inside the bearing, that higher viscosity inside the bearing is going to reduce the MOFT.
HTHS is generally relevant at idle, not so much at five, ten, twenty millions per second instead of the one million in HTHS. That's shear thinning and that's why you had to be pointed towards ultra shear... Those people and others weren't judging oils or grades, they were interested in the skills and tools of their time – ultimately the HTHS as such.
If a guy and his Honda used some LM 5W-50 and killed an egine or two, that's not much of a brand aspect here either, although the LM might have used one of the thinnest base oil blends. It's merely one more situation you troops can't deal with in any reasonable way, cause all your tools in any case are the hammer.
Whatever the viscosity inside the bearing is at operating conditions is still relevant. Yes, maybe the xW-50 oil they used didn't do well in those engines at high RPM and high temperatures due to HTHS inside the bearings falling way to low under those conditions. How do you explain motorcycles revving at 10,000+ RPM for long periods of time running xW-50 oils? Better oils? ... maybe those S2000 guys should be running motorcycle oil in their engines. It could have been that the specific oil they were using just wasn't up to the task, regardless of the viscosity. A lower viscosity oil
of the same exact formulation would be just as bad or probably even worse under the same engine conditions.
No, regarding oils, it's a fundamental feature, that a non-intelligent 5W-50 viscosity molecule gets properly slowly PD pump-motivated and warmed up en route, then after entrainment experiences more viscous heating while the VII components align and bow to the load under ultra shear – just in time for getting together as thin as possible when the load is maximized. What's the shear rate over a 50mm bearing roughly? Three times 50 x 150, divided by 1000 for meters, divided by OFT. Walks towards 20 millions per second. Not that much room for speculation. The thickness ain't there. The temperatures for VII-action would be there, but...
Almost every engine of course will have sufficient BOV from a 5W-50 under almost all conditons, but that's not really because of very advanced 5W-50 oils among others. It's simply because the actual viscosities in the bearings are usually sufficient anyway – as they'd be with an OSP SAE not-even-20 (or the 20W-20 from page 8, as long as temps are kept under control). The #50 is a primitive cure for temps not under control. Normally not ever a requirement as such.
That's why I asked if these S2000 guys who smoked the engine had any oil pressure and/or oil temperature data. Any oil cooler being used? If they had any engine data logging that could have maybe lead to some other factors involved. There are all kinds of factors that could be involved:
Was the oil crap to start with - bad formulation?
Were these cars modified in any way (turbos, tunes, etc)?
Was there any pre-ignition/knock events going on, which can cause big rod loads?
Were these engines rebuilt, and if so what were all the bearing clearances - maybe some setup too tight?
What condition were the bearings in before the top speed runs - previous damage?
Was the oil really a 50 to start with when new?
Was the oil level low?
What did the oil level go to during the top speed near redline use?
Was the oil sheared down a lot already from previous hard use and many miles?
Was the oil fuel diluted?
Was the oil filter new or did it have lots of miles and debris in it?
Was the oil filter free flowing enough at prolong high RPM?
Did the oil filter go into bypass and send a bunch of debris into the oiling system?
Was the oil filter cut open to ensure there was no media tearing, which could have sent some downstream?
As far as the PD pump (your favorite subject, lol), if in good shape, it would pump the same volume of hot oil if not in pressure relief. I highly doubt it was in relief with hot oil, regardless of viscosity. Was the pump modified in any way? Was the pressure relief working correctly? What is the pump pressure relief set to, and what was the max oil pressure seen during the top speed run?