And yes, any design engineer would place it around 0.4 (maybe upwards of 1). Put 8 cs in instead of 10 cs (again, 20 vs. 30), worst case moves the 0.4 to 0.3 ---> Not much movement on the Stribeck, obviously. The point.
Again, you are stating that you are GUESSING what a designer WOULD do...and using that to make your recommendation that running to the left is still hydrodynamic...you aren't even trying to use science, you are GUESSING what the designer's intent was, and GUESSINg that it will all turn out alright, all of the time.
Except that means that they LOSE their designer installed safety margin,...
The discussion was, in going from a 30 to a 20 weight, and we see that only moves the Stribeck a small amount. Emphasis on SMALL amount. Very little margin lost.
Again, you biring up Streibeck, as 'though it adds validity to your argument, when you are GUESSING at where on said curve it would be...at least others have the honesty to say that the manufacturer's have a margin, and short of overheating/tracking, you won't use it up in "normal use", rather than brigning in a curve that they have no comprehensible idea of where the designers put it...as you say, you could be out bu a factor of 2.5 (0.4 to 1), which if your GUESS is wrong puts it on the wrong side of hydrodynamic
The ZN/P for the crank journal bearings SPECIFICALLY remain hydrodynamic for running conditions, a very important point to remember.
Do they ?
that's not what the paper I linked said, nor what Honda say in some of their 16 grade documentation.
You are ASSuming that bearing remain hydrodynamic...in design, I would always make sure that a bearing is hydrodynamic, but my stuff is supposed to run for 200,000 hours, not achieve "adequate" life in a semi disposable appliance,subject to regulators like CAFE
End of discussion for me.
Yep, that is always a convincing point
I'll just let the "Improved Fuel Efficiency by Lubricant Design : A Review by R.I. Taylor & R.C. Coy, Shell Research & Technology Centre, Thornton, United Kingdom paper take it from here. Address all questions to Shell from now on please. LOL...
I'll bold what I consider to be an important flaw in your guesswork house of cards.
"In our laboratory, it has been observed that in a modern gasoline engine, well designed automotive bearings can be lubricated with oils as thin as 2.3 mPa.s (and a 20 weight oil has 2.6 to 2.9 mPas) without any observable wear on either con-rod or main bearings.
I agree with them, however, they are talking about bearings that are designed
for the lubricants and operating conditions. They are not saying that 2.3 will protect every engine that's ever been made, which is a common assertion on this site.
They are also not
* GUESSING on a designer's intent
* GUESSING where the designer put the bearing on the Streibeck Curve,
* calculating where the first guess would take them with a change in viscosity
* GUESSing that it will all therefore be OK; then
* making a recommendation on all engines, all designs, based on a card house of guesswork.
Even if the answer is correct (it doesn't fail), the train of thought to get to the conclusion is flawed, and illogical...
illogical UNLESS you KNOW where the bearing in question actually IS on the streibeck curve.
Otherwise "she'll be right" saves space on the message board.