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  #31 (permalink)  
Old 10-11-2008, 03:01 PM
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Quote:
Originally Posted by ScoTFrenzel
In reality concrete is compressable too,

But in practicality....... it seems dog gone solid if you hit it with your face.

I've felt concrete on my face.

In reality the materials you use for a given application need to withstand the stresses you put them under.

Concrete is compressable, that's why they compress it with long rods to pre stress the stuff for use in freeway overpasses and other long span applications.

Cast iron is compressable too, that's why you add stud girdles and splayed main caps to keep that characteristic from being a problem.

Someone mistakenly said fluids were incompressable. They were corrected. As already stated, for the applications we are talking about here, they might as well be incompressable.

A bearing is a controlled leak in a low pressure system, flow is important to maintain the film of oil. Compressability never even enters the equation..


Later, mikey

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  #32 (permalink)  
Old 10-11-2008, 04:21 PM
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Quote:
Originally Posted by powerrodsmike

A bearing is a controlled leak in a low pressure system, flow is important to maintain the film of oil. Compressability never even enters the equation..


Later, mikey
Interesting isn't it?
In reality, NOTHING gets lubed by pressure. Everything gets lubed AFTER the oil gets to the leak.

Pressure is the measurement of the resistence to flow of the delivery system. IF the leak is big enough, pressure is lower for the volume delivered. So I guess pressure is the way to measure the size of the leak.

Tighter clearances are smaller leaks. The tighter clearance also allows for less required volume to maintain the oil wedge that separates the surfaces.

For those who might disagree, remember many car engines did not have oil pumps but only relied on splash oil to lube bearings, as do many lawn mowers, etc.

Note, anytime the pressure maximum set by the bypass valve is reached, the pressure AND flow remains constant and the excess flow is recycled to the inlet.

never mind
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  #33 (permalink)  
Old 10-11-2008, 04:32 PM
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Seriously,

One of the exercises we did in engineering school lab was to demonstrate the viscosity of engine oils.
Try this=

get room temperature 5w30, 70*f
get some 5w30 heated to 200*f

Which one is runnier/thinner?

People sometimes worry about 5w being too thin when you first start your engine in the summer time..... look how thin 30w is when it is hot.

5w20 used in these new cars is just plain scary it is so thin when hot.

Makes me want to use 0w40.
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  #34 (permalink)  
Old 10-11-2008, 05:23 PM
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IIRC, 5w 30 wt oil at 200*f is thinner than water.
I still like the idea of having the higher pressure you get from a HV pump...it seems to me that you'd be making sure that the oil has no excuse to get to the far reaching ends of the system. Even when the clearances get big. ( I run my stuff till the very end.... )

Now that you mention splash oiling, what about the metal to metal contact points that still only get oiled by splash...Cam lobes, lifter bases, rocker arms, valve guides, distributer gears, timing chains..lots of moving parts getting lubed with only the oil thrown away by their neighbors.

Later, mikey
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  #35 (permalink)  
Old 10-11-2008, 05:27 PM
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Quote:
Originally Posted by powerrodsmike
IIRC,


Now that you mention splash oiling, what about the metal to metal contact points that still only get oiled by splash...Cam lobes, lifter bases, rocker arms, valve guides, distributer gears, timing chains..lots of moving parts getting lubed with only the oil thrown away by their neighbors.

Later, mikey
Makes a good case for ZDDP, doesn't it?
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  #36 (permalink)  
Old 10-12-2008, 08:46 PM
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oil pressure

Hey guys Not to hi-jack but I got a question on this subject. I got my motor (SBC 355) from a guy that owed me money for puttin a tranny in his blazer and supplyin him a good 700R4. Anyhow when I got it he said It had about been broke in per cam specs, then driven about 300 miles city and HWY, then he put it in a Chevy luv mud drag truck and put about 15-20 passes on it. When he had it, He was not running a PVC and had a old junk 750DP on it that was runnin way to rich or flooding (102 octane). He said It fouled plugs about every 3 passes, and the oil reeeeeeekkkked of gas when I got it.

I think I may have been thinking bass ackwards on this. I thought that a thinner oil would give you higher pressure cuz Its able to flow more freely, but it was just the opposite.
When I got the motor I drained the old oil, that smelled of gas very badly and was really quite thin by my standards. Infact I actually had a thread here about titled stinky oil I primed it and then started it to warm it up before draining, and It had about 15-20 PSI at idle. I filled It back up with valvoline 4qts 10w30 and 1qt lucas oil stabilizer, and it had about 50 psi warm with the new oil. Is It normal to see this much of an increase in psi?? JSYK, the no longer gets stinky and has held the same PSI since I've had it.
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  #37 (permalink)  
Old 10-13-2008, 10:35 AM
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It is normal considering what you drained out.
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  #38 (permalink)  
Old 10-13-2008, 12:18 PM
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For the last qt to add use a qt of Marvel Mystery Oil. It will lower the viscosity and still lube correctly.
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  #39 (permalink)  
Old 10-14-2008, 02:48 PM
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Quote:
Originally Posted by powerrodsmike
Actually, they do. Check your physics books.

Look under "compressibility of fluids".

Here is one that I found just by googling that term.

http://www.engineersedge.com/lubrica...ulic_fluid.htm

'nother one. With chinese algebra.

http://www.engineeringtoolbox.com/bu...ity-d_585.html

It's not enough to worry about in an engine, as the pressures are so comparatively low that they will never reach the point where they will compress. Viscosity the important characteristic of oil .

It's a known fact that brake fluid compresses, silicone more than glycol based fluids. It compresses even more when water is absorbed.
http://www.afcoracing.com/tech_pages/fluid.shtml

Later, mikey

lol, come on mike, 1000-4000 PSI for a 0.5 percent reduction in fluid volume? Sure, any time you add pressure or reduce temperature you can fit more molecules in a given volume. PV=NRT. I didn't think I had to mention that for this discussion because for our purposes, fluids don't compress (or enough to worry about).

Second, you can consider compression using pressure to fit more molecules in a given space. IF you could lubricate a crank case with a gas and you started putting pressure behind it you're using force to pack more molecules into the same amount of space. You're compressing the gas.

You just made the distinction that fluids compress to a very small degree. That pressure you're reading on your oil pressure gauge is absolutely a small degree of compression on that oil.

K
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  #40 (permalink)  
Old 10-14-2008, 04:12 PM
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I know, I even said that compressibility doesn't matter for our application, wrote it a couple of times... so did Rob. But it's fun to find the slightest inaccuracy in someone's statement and turn it into a whole 'nother topic...



hahahahahahaha

Later, mikey
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  #41 (permalink)  
Old 10-14-2008, 07:06 PM
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Quote:
Originally Posted by powerrodsmike
I know, I even said that compressibility doesn't matter for our application, wrote it a couple of times... so did Rob. But it's fun to find the slightest inaccuracy in someone's statement and turn it into a whole 'nother topic...



hahahahahahaha

Later, mikey
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  #42 (permalink)  
Old 10-14-2008, 08:15 PM
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Since the discussion has gone off to China carrying a Football Bat........

I have to ask the same question as Curtis73,

Why use 20w50 oil?

I'd also like to know precisely who is building engines loose enough that would require 20w50 to maintain a decent pressure reading? Huge bearing clearance and thick oil is a bad idea, these days, on anything less than a blown drag engine making a LOT of boost. Think Blown Alcohol/Blown Pro Mod.

Once upon a time thick oil was a necessary evil on race engines. Modern engine building techniques, along with modern machining practices and equipment, have negated the necessity of thick oil on anything but the highest levels of horsepower making. It's only necessary in those situations because of the extreme shock loads and fuel blowby contaminating the oil at a rapid rate.



Larry
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  #43 (permalink)  
Old 10-14-2008, 09:30 PM
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Cope,

Short answer to your question:

With the pressures you have I'd say ~50 - 60 Deg is as cold as I'd go...


Long answer as to why I think that,

IMHO

Curtis gave you some very good advice. 10 PSI/ 1000 rpm is all you need to maintain, anything more is wasted HP. I'm glad your engine builder has a good reputation and I'm sure it was earned over his 25 years of experience. It WAS common practice to use very heavy oils years ago for a lot of reasons but the biggest was that multi-viscosity oils weren't that good back then. Those polymer viscosity improvers can fail at extreme temps and pressures causing them to collapse. When that happens you are left with the viscosity of the base oil. So a 5w-40 would become a 5W oil which may not have the film strength needed in the extreme conditions that caused the VIs to fail. That was why either straight grade oils (40W or 50W) or the heavy based multi viscosity (15W-40 or 20W-50) oils were the choice of many race engine builders. Oils have improved tremendously since then. Many big dollar racing teams (the ones with 6 figure R&D budgets!) use some very thin oils these days. The new way of thinking is anymore pressure than is needed to properly lubricate the engine is a waste of HP. Another thing oil does is take heat away from places that the water never sees like the bearings, cam, valve springs, etc. The more oil that moves past them the cooler they run. Thinner oils have the edge here.

A concern about heavy oils in cold weather is that it can take awhile for it to get to where it needs to be on cold start, leading to more engine wear. The oil drains back to the pan much more slowly also. At the extreme, (especially if you have a high volume oil pump) A few too many RPM's while the oil is still cold and you can end up with all of your oil in the valve covers and none in the pan If you run an oil temp gauge you may have noticed that the oil heats up much more slowly than the coolant. If you don't have an oil temp gauge you could think the engine is warm but still have oil that is very thick and not draining.

This is my opinion on the subject, I hope it helps. I guaranty it's worth every penny you paid for it...
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  #44 (permalink)  
Old 10-14-2008, 09:41 PM
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thanks slowgta thats makes alot of sense clears up alot without getting all technical

Last edited by cope; 10-14-2008 at 09:48 PM.
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  #45 (permalink)  
Old 10-14-2008, 09:52 PM
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Glad it helped..
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