It is the Stribeck curve. Journal bearings and lower piston rings in an engine are the only places that run in the hydrodynamic lubrication regime. Everything else runs in the mixed lubrication and/or boundary lubrication regimes, where the thickness of the oil film is minimal. It is all about geometry. You don't have the geometry that allows a thick oil film in most parts of the engine. That's why the shear rates everywhere else are up to 2,000 times higher than in the journal bearings.
The MOFT can't be thin enough to be 2,000 times the shear rate in a journal bearing. No place in the engine will the shear rate be 2,000 times more than it is in the journal bearings.
What do you mean by assume? How do you get the MOFT by assumption? Valvetrain runs in the boundary lubrication regime, with metal-to-metal contact. The same is true for the upper piston rings, where you get metal-to-metal contact. By geometry, I don't mean how to calculate the relative speed—I mean how the sliding parts rub against each other. Two concentric cylinders won't be in the same area on the Stribeck curve as a pointed object pressing on a flat surface or some other pointed object. That's going to greatly increase the load on the oil film, which will squeeze it out.
What do you think the MOFT is then between a cam lobe and flat lifter? We all know that wear mitigation on valve train components depends greatly on film strength due to AF/AW additives. So that basically means that it doesn't matter much what the oil viscosity is in the valve train if the MOFT is basically zero as you say. But I think there has to be some effective MOFT in the valve train because it can certainly be in the mixed lubrication regime (Stribeck curve) when the RPM is higher.
Best description I can think of is a pleasant but interesting tone derived from the combination of intake and exhaust sounds. You're free to rename it. Nonetheless is was how it sounds when going up a hill at 3/4 throttle. Wish we still had the emoji of the guy driving and shifting"
Valvetrain runs somewhere between the boundary and mixed lubrication regimes. I don't know how thick the oil film is, but using your speed values and the shear rates from the Shell paper, I get as little as 26 nanometer or 260 angstrom at peak shear rates. Therefore, you get surface asperities contacting each other. Oil is still essential to lubrication, even in this regime, in fact even more so, as you want the best help from the oil possible. You want the thickest base oil possible for the least valvetrain wear. There are studies that show that thicker base oil reduces the valvetrain wear.
And how much of the reduced cam-chain wear was due to the base oil viscosity vs the AF/AW additives (also a goal of API SP specification regardless of viscosity) they speak of? What was the max shear rate going on in the chain components?
Good reference. The oil film is still 20 times thinner at 3,000 rpm than the 2 microns you assumed, which puts the shear rate at around 5×10⁷ s⁻¹, well into the regime where the VII fully temporary-shears and you're left with the viscosity of the base oil and an additional viscosity contribution coming from the DDI pack.
Could be ... but that's only around 10 times more shear ... not 2,000 times more like you mentioned in post #41. Plus, if you bring the engine RPM down to 2,000 to 3,000 like in normal street driving it cuts the shear rate down by 2 to 3 times. Plus, oil temps on the street running below 150C helps keep the viscosity under shear conditions higher than what the HTHS and HTFS would be at the defined 150C. I think the HTFS window on a normally driven street car is a very small and rare window to see in real life driving conditions, unless someone was in a high speed police chase going 120+ MPH for an hour, lol.
I've always believed an increase in engine noise, oil related or not, to not be a good thing.
How many people here were believers in Castrol Magnatech original formula being quieter, smoother etc? I was not one of them but they couldn't have all been wrong.
Oil is also crucial in the boundary lubrication regime, and unlike in the hydrodynamic lubrication regime, the viscosity becomes directly related to wear in the boundary lubrication regime, as opposed to having minimal or no effect on wear if it is above a certain minimum in the hydrodynamic lubrication regime.
www.semanticscholar.org
Magnatec was definitely the best oil in smoothness, responsiveness, and quietness, until I tried Edge bb. The Edge blows it away in those categories.
It’s the good feel of fresh oil. Nothing more.
I actually notice engine smoothness “kicks in” per se after the oil is good and settled in, once it’s been run for a few days.
Thinner but maybe tackier? Just saying no science to back my statement.
