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Engine oil press
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59 in Calif
Posted 2018-01-28 1:13 AM (#557077)
Subject: Engine oil press


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Hey Guys, Here's something to think about. It may take a college engineering degree to answer this question. Will 20W eng oil withstand the force placed on it at the crankshaft under a full power situation equally as well as 30W oil. With 50 - 60 PSI oil press. I suspect the determining factor here would be crankshaft tolerences. What do you guys think ?? Jerry
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Powerflite
Posted 2018-01-28 1:57 AM (#557078 - in reply to #557077)
Subject: Re: Engine oil press



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Liquids in general are mostly incompressible which means that if you filled a system and capped the ends off, that the crank would have to move the fluid from one side of the crank to the other side of the crank in order for the bearing to make contact with it. This movement takes time to accomplish - especially with small clearances for the liquid to move in. The movement of the liquid is hindered by the viscosity of the fluid and the resulting boundary layer, which is thicker with higher viscosities. As long as the time required to move the liquid around is longer than the average time for the piston to move, it should be fine. This simple look is dis-regarding the pressure and flow of the oil, but the pressure really just keeps the fluid in place because the system isn't capped off and is always moving. It also provides a centering force for when the motor first starts firing. The viscosity acts as a force that prevents displacement of the crank in a similar way that pressure does - especially at higher rpm. So I expect that a higher viscosity oil will make it easier to prevent bearing failure, but will make the pump work harder and will increase parasitic losses due to higher friction. Crank clearance is closely related to the viscosity value because of the boundary layer that I mentioned. Bigger clearances means that the fluid is able to flow easier because it is further away from the boundary layer, thus you will require a higher viscosity oil to keep the same boundary layer effect and maintain the same level of protection. The best solution to this situation is to create very tight clearances with very low viscosity oil because then you decrease the friction and maintain a sufficient level of protection.

But to answer your question with numbers - is one sufficient vs. another one at a certain pressure, with certain clearances and flow rate - who knows this except by trial and error, or by rules of thumb that were derived by trial and error?
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wayfarer
Posted 2018-01-28 11:54 AM (#557095 - in reply to #557077)
Subject: Re: Engine oil press



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Very good dissertation.

Ponder this; The last time I looked at a NASCAR engine they were using 0-5wt oil and some darn fine crank grinding for miniscule clearance. It sure seems to work.
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58coupe
Posted 2018-01-28 12:35 PM (#557097 - in reply to #557077)
Subject: Re: Engine oil press



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I think you should take advantage of the progress that has been made in oil technology and run a multi-grade oil. Just because 50-60 years ago straight grade oils were listed for use in our FLs doesn't mean that we need to use them. In fact, because of the environment I live in I use a lot of synthetic oils because of their better cold and hot characteristics over conventional oils. All you have to do is tear down an old engine made 60 years ago and compare with a modern engine with the same mileage and see how much cleaner they are inside, assuming proper maintenance, this is because of the better quality oils we have today.
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Powerflite
Posted 2018-01-28 1:43 PM (#557100 - in reply to #557077)
Subject: Re: Engine oil press



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....and detergents that are incorporated into them.
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1960fury
Posted 2018-01-28 1:53 PM (#557103 - in reply to #557097)
Subject: Re: Engine oil press



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58coupe - 2018-01-28 12:35 PM

I think you should take advantage of the progress that has been made in oil technology and run a multi-grade oil. Just because 50-60 years ago straight grade oils were listed for use in our FLs


are they? don't have a fsm at hand but i recall they listed multigrade oils (1960 plymouth fsm). so these single grade oils were already obsolete when our cars were new. who, for heavens sake, still runs these oils?! motor oil is a bad thing to save money with. my car gets the best thats available, no matter what it costs.
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LostDeere59
Posted 2018-01-28 2:04 PM (#557106 - in reply to #557077)
Subject: RE: Engine oil press



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I think another factor here is the shear strength of current technology oils vs. older technology oils, independent of the viscosity.

Viscosity used to be a primary determining factor in shear strength as most non-synthetic oils were similar enough that the viscosity measurement was sufficient to provide a guideline for shear strength.

With the advent of synthetics, synthetic blends, and improved non-synthetic oils, the importance of viscosity in and of itself has to a large degree vanished, but because it's a familiar term and there is no convenient replacement we continue to use it for marketing purposes.

Current technology premium oils can withstand much, much, higher loads at much smaller clearances and 0 viscosities than any oil from 3 or 4 decades ago.


Gregg
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Powerflite
Posted 2018-01-28 2:53 PM (#557111 - in reply to #557106)
Subject: RE: Engine oil press



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Please educate me Gregg. I have only heard of shear strength being used to describe the movement of solids, not liquids. How and why are they using it for these oils? Is it because they are limiting their view to only the region well within the boundary layer where the liquid acts less like a liquid?

Edited by Powerflite 2018-01-28 3:00 PM
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57chizler
Posted 2018-01-28 4:48 PM (#557114 - in reply to #557078)
Subject: Re: Engine oil press



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Call me cynical but I believe the sole purpose of using light weight oils in newer cars is to improve corporate fuel economy (CAFE).
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LostDeere59
Posted 2018-01-28 6:29 PM (#557119 - in reply to #557114)
Subject: Re: Engine oil press



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57chizler - 2018-01-28 4:48 PM


Call me cynical but I believe the sole purpose of using light weight oils in newer cars is to improve corporate fuel economy (CAFE).


Ok, you're cynical.

But not completely incorrect. In truth under current government and market pressures ANYthing that improves the efficiency and power output of an engine will be considered and often used. I recently read an interesting article regarding camless engines which went into some detail regarding the overall efficiencies and possible gains these systems would allow with current technologies. I was surprised at the detailed analysis that goes into considering engine modifications of this level of complexity.

Of course the ability of modern oils to provide better protection to engine components that are being engineered closer and closer to their failure limits is a factor as well.

Powerflite - I cannot claim an engineering education or knowledge as deep and wide as yours seems to be - my time in college was cut short, and my subsequent career and education in the automotive field as a technician rarely delves quite so deep into theory as your knowledge seems to be. That being said I will always defer to someone with better education and experience than I have. My knowledge of "shear strength" is collected from various articles and publications I have read over the last few years regarding the development of lubricating oils, engine oils in particular. Some of this information has come down through the manufacturer I work for, most of it from other varied sources. What I have gathered is that modern oils by virtue of better molecular structures resulting from better refining, additives, and of course synthetic supplements or full synthetic make-ups, have the innate ability to resist the "crushing" or "shear" forces created by not just crankshaft and piston/ring pressure, but the wiping forces created by their movement. Because of this these oils are less dependent on their physical "thickness" or viscocsity than their predecessors, and can provide better protection to the components at much thinner viscosities. As you well know this allows for less pumping losses, less drag within the bearing areas, and better non-pressurized flow such as oil return to the pan or reservoir. I'm also under the impression that the tighter bearing clearances in modern engines using these oils is kind of a "chicken or the egg" argument - thinner oils exit the bearing areas faster which makes a tighter clearance necessary to maintain both pressure and lubricant function, but tighter clearances require a thinner oil to allow proper inflow and dispersal, especially under operating conditions. Like many things it seems to be a hand-in-hand situation.

As an interesting aside I recall reading many years ago that Smokey Yunick took the time to build a small block Chevrolet engine fitted with roller bearings throughout in search of additional power. I can imagine the time and effort it took to replace the crankshaft main bearings, rod bearings, and camshaft bearings, was substantial. In the end he found that the "break-away" torque, or effort it took to start the engine spinning was significantly reduced, but the running loss was exactly the same, and the actual HP output of the engine varied by so little as to be negligible. He theorized (no doubt correctly) that the frictional losses of the rings in the cylinders comprised most of the drag, and that once an engine is making oil pressure and the bearing surfaces are filled, the cam and crankshaft are truly floating in oil and present little to no appreciable drag or loss. He abandoned the project since he was seeking horsepower, and was unconcerned with easier engine starting since it was not an issue.

I'd also like to note that this evolution is not just in engine oils. Gear lubes as well are now being used with "out-of-the-bottle" viscosities approaching that of water, yet they provide much better lubrication and impact resistance. The appearance of "dual-mass" flywheels is a direct result of this change in lubricant technologies as the much lighter gear oils (which substantially reduce running losses in the gearcase) allow the crankshaft dynamics (acceleration/deceleration with cylinder firing) to cause chatter or rattling in the transmission gearsets. The entire purpose of the dual-mass flywheel is to dampen the crankshafts rotational pulses and quiet the transmission noise.


Gregg

Edited by LostDeere59 2018-01-28 6:47 PM
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Shep
Posted 2018-01-28 7:20 PM (#557126 - in reply to #557119)
Subject: Re: Engine oil press



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Very interesting thread, back in the day I raced and toured with a 64 Ply Max Wedge 426. At first I set up a high pressure oil pump and used 50 weight oil. A few years down the road I thought, this is a finely blue printed engine this high pressure system and heavy oil is dragging the engine down..re engineered the oil pump and started using early version Amsoil synthetic. At 30 weight. With no other changes the car averaged almost a tenth quicker ets and 1.5 mph better trap speeds. The oil pressure went from 75 psi hot to only 50 psi at, 6500 rpms.

Edited by Shep 2018-01-28 8:37 PM
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BigBlockMopar
Posted 2018-01-29 6:52 AM (#557150 - in reply to #557077)
Subject: Re: Engine oil press



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I daily drive my 318ci '73 Dodge Dart with 0w20 synthetic oil in the crankcase.
After a good highway trip where everything is fully warmed up and heatsoaked, the oil pressure will only get as low as 24-25 psi, with the engine idling in Drive at 550-600rpm.
Now this engine has a low compression ratio of just 8.6:1, so cylinder pressure isn't that high of a higher performance engine.

What I noticed was when I switched down from the 10w40 to a 5w20 semi-synthetic oil, was the engine's operating temp was 15 degrees F lower.
Imagine how much internal friction and load has been freed up internally for an engine to run 15 degrees lower.
I started using 0w20 later on because I found a cheap source of it.

Oil technology is also about the oil being able to form a 'wedge' between the rotating crank and bearings. Oil gets pulled in inbetween the metals and forms a film due to the rotational speed of the crank.
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