Oils, cavitation and viscosity

quote:

Originally posted by Aus Ford:
Given the 351c oil system cavitation issues would it not be benificial to use a oil with a viscosity toward the thinner end of the recommend ie: 10w40 rather than 20w50 ?

What are the thoughts out there about synthetic oils and their cavitation resistance ?

This is the first that I've heard about a cavitation issue.

The 20-50 recommendation came about as a Ford recommendation for the production Boss 351.

To me a 20 weight winter grade has always been questionable. I would take a guess and say that what the engineers wanted was the 50 weight and the only way available back then in multigrade was the 20-50.

Personally I feel with the availability of relatively inexpensive full synthetic like Mobil1, a 10-30 or 10-40 is fine for even racing use in this engine.


Oil weight really is going to be determined by the clearances that the engine has on the main bearings. The greater the clearances the thicker the viscosity of the oil needs to be.

I would think if you maintain 1.5 thousands clearances on those bearings a standard weight oil would be fine?


I never heard of the C oil pump having cavitation, or sucking air, at any rpm. These engines have been raced hard since the beginning of their introduction and the significant oiling modification for sustain high rpm is to restrict oil through the lifter galleries.

The designs of the Cleveland oil pumps is no different than any other engine. for racing purposes it is recommended to braze the oil pickup tube to the oil pump body but that's just to keep the tube from vibrating loose.

Another issue with racing them in NASCAR that was attributed to oiling issues was valve spring failure.

That was corrected in changing the oil drain back rate in the cylinder head. What was needed was to bathe the valve springs in oil to cool them to prevent failure.

You need to maintain about 1.5 to 2 inches of oil in the valve cover to cover the valve springs for cooling purposes FOR ENDURANCE TYPE RACING. Street cars do not need this.

That was done on the racing heads by changing the drain back holes in the heads. Also using the Ford Boss 302 drain back hose modification to the valve covers would be the opposite of what you want in a racing Cleveland.

I do not know if the T/A Boss 302's had this issue at all.

I've been using Amsoil & Bel Ray synthetic oils in my motorcycles since the 1980s with great success. I've used Mobil 1 synthetic oils in my cars since the early 1990s, also with great success. I'm not aware that synthetic oils resist cavitation any better however.

10W oils are good for use in a Cleveland set-up with standard type bearing clearances. As are 15W and 20W oils. Standard main bearing clearances for street performance being 0.0020” to 0.0025” and standard rod bearing clearances being 0.0025” to 0.0030”. The guys I know using 10W oil in their race engines use 10W30, not 10W40. The 10W viscosities may resist cavitation a little better than 15W or 20W, but enough to make a difference? I can't say. What the thinner viscosities will do a little better is make the sharp 90 degree turn off the main oil passage into the branches which feed the center 3 main bearings. Therefore they flow a little more oil to the rod bearings, and keep the bearings a little cooler.

FYI Ford's original recommendation for the 351C here in the states was 20W40. But 20W40 didn't stay on the shelves long, by the late 1970s it was replaced by 20W50. 20W50 was the standard for several decades. In the last decade I've seen 10W30 become more popular while 20W50 has fallen out of popularity.

You shouldn't use thinner oil (0W or 5W) unless the main & rod bearings clearances are set-up tighter and more precisely for the thinner oils. If the bearings are set-up tight, then consider synthetic oil a necessity, because the bearing temperatures run hotter. Also, if you're using the thinner oils (0W or 5W) don't use fully groove main bearings either, use 3/4 groove main bearings instead. Finally, since the 0W and 5W oils will tend to squirt more easily out all the unproductive clearances; tappet bore bushings become more of a necessity with those ultra-low viscosity oils.

-G

A point of clarification, the "W" part of the viscosity grade designation indicates cold temperature performance only. The second number is the operating temperature (210*F) viscosity. A 5W-50 is the exact same oil as a 20W-50 at operating temperature, however the 5W-X will flow a lot better cold - not a bad thing, but unnecessary for mild temperatures like So-Cal or summer anywhere else.

The #1 benefit of synthetics is they do not oxidize as readily as conventional oil, and that keeps your motor clean of deposits. The #2 benefit is they naturally have a broader viscosity index. That means they can be formulated with less viscosity improving additives, that eventually shear down over time.

I think that with full synthetic and natural oil, we are really talking about two different animals.

Full synthetic flows much better than natural does at low temps and maintains viscosity much better at high temps.

It doesn't break down viscosity wise the same as natural does.

To compare the two is really talking apples and oranges with an engineering "interpreter" in between trying to translate.

The 20-50 was done at a time when essentially only natural oils were available.

There were variations in that such as full Pennsylvania grade like Penn State. To me that was the absolute best of any natural oil ever marketed to the general public.

It no longer exists as full Pennsylvania grade and now is just a blend.

The other was mineral oil which I don't know much about other than it is not compatable with the other oils.

I like Mobil1 full synthetic. It has been run in race cars for around 40 years now and has shown nothing but superior characteristics at every scientific comparison.

The "ice truckers" have different issues that even full synthetic doesn't solve but unless you are constantly running well below zero Farenheit Mobil1 will do you fine.

When you rebuild you want to maintain about 1.5 thousands clearance on your bearings. If you do, even 10-30 is fine.

It has to do with film strength of the oil.

Mobil1 likes to say that it just isn't oil, it's "liquid engineering". I can't say as I argue with that.

I think also that if your engine is having issues with wet sump oil cavitation then you should be running a dry sump system.

If that doesn't work for you, take up a different hobby altogether like hot air ballooning? There is no engine oil involved in that at all?

quote:

Originally posted by PanteraDoug:


This is the first that I've heard about a cavitation issue.



I never heard of the C oil pump having cavitation, or sucking air, at any rpm. These engines have been raced hard since the beginning of their introduction and the significant oiling modification for sustain high rpm is to restrict oil through the lifter galleries.

The designs of the Cleveland oil pumps is no different than any other engine. for racing purposes it is recommended to braze the oil pickup tube to the oil pump body but that's just to keep the tube from vibrating loose.

I was referring to some things mentioned in Sticky 3:

Quote from sticky 3:
The diagnosis of this problem which I find most compelling is based on hydraulic system engineering; Roy Johnson suggests the problem is cavitation which occurs first at the oil pump. Jon Kaase has commented “what the 351C needs is not a high volume oil pump but a standard oil pump with dual inlets”.

Johnson has further suggested cavitation manifests again in the main lubrication passages resulting in a sag in oil pressure in the middle of each passage as engine speed increases.

The large ports connecting each tappet bore to one of the two oil passages expose the motion of the tappets to the oil passages.

Jim Kuntz has commented on the detrimental effect of the "lifters chopping up and down in the main oil supply". Thus cavitation resulting from the rapid motion of the tappets spreads to the oil passages through these ports.

As the clearance between the tappets and the tappet bores increases so does the severity of cavitation. So as a motor gets older the lubrication system cavitates worse.


Has anyone seen a pump with dual inlets for the 351c ?


I do some work with hydraulics myself and i often thought that the 351c may have some cavitation issues effecting lubrication quality.

Industral hydraulic pumps with smaller volume than the 351c pump would have larger inlets, maybe 1" or 1 1/4"NPT and they spin more slowly than a 351c pump, maybe only 1440rpm, so if the 351c pump doesn't cavitate at all that pump would be pretty outstanding.

I've had 351c and 302c engines in cars that have been well maintained, oil changes done on time or even early with top quality oils and filters used, never left with low oil level and have not been driven hard and on teardown had all the bearings worn down to the base metal.

I do feel there is more to the subject than just straight common sense may suggest....??

A interesting animation of cavitation inside a gerotor pump.



Gerotors usually require the depth of the inlet ports to be at least the same as the width of the gerotor.

The ports in the 351c pump are less than that.

I think the opinion given in Sticky 3 about the 351c pump needing two inlets is correct.

The wide 351c gerotor needs to be fed oil from both sides instead of just one.

This animation shows a deep inlet port below the gerotor and a narrow "shadow port" above. Note the constant cavitation in the shadow port and cavitation in almost 3/4 of the gerotor.

quote:

351c pump needing two inlets is correct.

Or the 10 quart oil pan with the proper pick up and baffles in the pan probably accomplish the same thing ... one thing for sure if you have 2 pickups ( inlets ) and one runs dry ... you still have the pump sucking air ... and the second will surely not suck oil from the pan. So not sure what the basis of two inlet would accomplish ? Temperature and vaporizing are a major contributing factor. So maybe an oil cooler would help.

[/QUOTE]Or the 10 quart oil pan with the proper pick up and baffles in the pan probably accomplish the same thing ..[/QUOTE]


If cavitation is taking place 44 gallons of oil will not help, boat propellers cavitate and they are in an entire ocean of water. Also Maybe not everyone can fit a larger pan, i wish i could fit a 10 quart pan in my car.



[/QUOTE]one thing for sure if you have 2 pickups ( inlets ) and one runs dry ... you still have the pump sucking air ... and the second will surely not suck oil from the pan.[/QUOTE]

True.....the two pick up tubes would need to come together to the same pickup point and be connected to the same pickup.


[/QUOTE] So not sure what the basis of two inlet would accomplish ? Temperature and vaporizing are a major contributing factor. So maybe an oil cooler would help.[/QUOTE]


Two inlets would slow the velocity of the incoming oil by 50 percent and could feed the gerotor from both sides instead of just one side. Single inlet gerotors are more prone to cavitation.

Yes an oil cooler is always a good thing !

quote:

If cavitation is taking place 44 gallons of oil will not help, boat propellers cavitate and they are in an entire ocean of water. Also Maybe not everyone can fit a larger pan, i wish i could fit a 10 quart pan in my car.

There are two companies that make a high capacity 10 qt pan for the Pantera.


The screen in the pickup is not only to screen out debris but to remove air bubbles from the incoming oil ... which could be generated by overhead oil / vaporizing. The larger 10 quart oil pan MADE for the Pantera doubles the capacity of the oil and displacing more surface area with the potential of cooler oil and since its in fact a closed system and not the entire ocean ... cavitation can be prevented.
I think the Competition Cars pretty much have it sorted out ... no reason to reinvent the wheel.

If you don't have a Pantera, there are also 9 quart pans made in the T configuration to fit Mustangs and other cars made by Canton, Aviaid, and Armondo that virtually eliminate cavitation.

There is a Chevy, Camaro/Corvette Aviaid pan. It has one advantage. It has a swing pickup and the pickup moves with the g-forces generated. It is Chevy only. Fords don't need it.

Cars that still have issues need to go to a drysump system.

I'm in with the Aviaid in the Pantera and a Canton road race pan on my Shelby.

Personally I worry about messing up the finish on the pans, not cavitation.

This isn't even worthy of mention in "Conspiracy Theory". I don't loose sleep over it.

quote:

Personally I worry about messing up the finish on the pans, not cavitation.

LOL ... exactly.

I'm sorry but i feel we are not reading from the same prayer book.

quote:

Originally posted by accobra:
The screen in the pickup is not only to screen out debris but to remove air bubbles from the incoming oil ... which could be generated by overhead oil / vaporizing.

Cavitation is NOT air bubbles in the incoming oil.

Cavitation should not be confused with Aeration.

Cavitation is the inability of the oil to flow into the pump at a rate equal to that at which the oil is being pumped out.

It is a phenomenon that takes place internally inside the pump, if it is taking place no amount of oil in the sump or sump design will have any influence over it.

It is essentially a cavity, a void in the oil, it does not consist of air but rather vacuum. In liquids with low boiling points and high vapor pressures it can contain that liquid in vaporised form.

Motor oil will smoke and catch fire usually before it reaches boiling (more than 300 degrees) so it's vapor pressure even when hot is such that it's viscosity is more of a influence on cavitation.

Cooling the oil will in fact make it worse as the oil at higher viscosity will be more resistant to flowing into the pump and through the pump's ports.

It cannot be observed externally (unless you had a pump and engine made of glass) and it decreases the efficiency of the pump especially as the pump speed increases.

Also increasing the pump size (high volume pump) will make it worse not better. Possibly the reason why many oppose the use of high volume pumps.




I couldn't give two hoots about the finish on the pan.

Cavitation occurs when a moving mechanical part moves so quickly that the fluid which it is contact with cannot keep up. Since the fluid cannot move as quickly as the mechanical part, it sheers away from the moving part, creating a void. Cavitation is most likely to occur when there is a relatively large clearance between a moving part and a stationary part, or a large clearance between two moving parts. Tight clearances serve to inhibit the creation of voids.

The results of cavitation manifest in many ways. A cavitating water pump will produce a noise that sounds like marbles banging around inside the pump. Cavitation will erode the impeller of a pump. And cavitation will double the amount of energy required to rotate a pump. Cavitation will occur at the interface between a turning crankshaft and the bearings that support the shaft, bearing erosion will occur as a result. Cavitation is not limited to rotating parts either. Cavitation can take place with parts having linear motion too, as in the case of the 351C tappets. The large port in the wall of each tappet bore provides the clearance needed for the oil to sheer away from the tappet as it moves up and down within the bore.

On the subject of oil pumps, I can show you Ford literature from the 1960s recommending 3/4" ID for the oil pump suction line of a high performance motor, yet the largest suction line you can screw into a 351C oil pump has an ID of 5/8". As Homer Simpson would say ... DOH!

There are several reasons for not using a high volume pump in the 351C. First of all, it is seldom mentioned, but the 351C was equipped with a high volume pump from the factory. The volume of the 351C oil pump is quite a bit higher than the oil pump in Ford's other engines. Second, the additional volume of a high volume oil pump is just going to squirt more oil through the non-productive clearances unless something is done to prevent it (tappet bore bushings). And if you do something to prevent oil being wasted in the non-productive clearances you'll find you no longer need the extra capacity of the high volume pump. Third, a high volume oil pump may pump more oil to the valve train, or pump oil to the valve train at a higher rate, thereby emptying the oil pan more quickly. Fourth, a high volume oil pump may sling more oil from the bearing clearances, loading the cylinder walls with more oil and overwhelming the oil rings ability to scrape oil off the cylinder walls. Fifth, as you've already mentioned, since the size of the suction line remains unchanged, a high volume oil pump will cavitate worse than the standard pump. Sixth, a pump can only push a certain amount of oil through the passages in the 351C block at any given pressure, to increase the flow of oil the pressure must be increased, but if a high volume pump has the same oil pressure spring as the standard pump it will not increase oil flow, it will simply recirculate the additional oil back to the pump inlet. So what happens, the high volume pump pumps more oil through the motor at low rpm, but once the oil pressure reaches the setting of the spring, then the amount of oil delivered to the block will be the same. As a result there's no change in oil flow at higher rpm.

quote:

Originally posted by Aus Ford:

I couldn't give two hoots about the finish on the pan.

You are missing the point. The finish on the pan is at least twice as important as this cavitation issue, and the finish isn't very important at all.

This engine has been run in production and competition for over 40 years. This issue has yet to manifest itself.

quote:

Originally posted by PanteraDoug:

You are missing the point. The finish on the pan is at least twice as important as this cavitation issue, and the finish isn't very important at all.

This engine has been run in production and competition for over 40 years. This issue has yet to manifest itself.

That's cool. To each their own.

quote:

Originally posted by PanteraDoug:

... cavitation ... This issue has yet to manifest itself.

An intelligent & professional practitioner of the hot rodding arts, who is also a hydraulic engineer from the aviation industry, claims cavitation and leakage have been the issues with the 351C lubrication system all along. Others have intuitively hinted at the issue without labeling the problem as cavitation. I found the diagnosis compelling, so I consulted a couple of hydraulic engineers I know from my career in industry; after looking into the situation they fully agreed with the diagnosis, as though it was rather matter of fact. One commented "of course the tappets are going to cavitate at high speed".

quote:

Originally posted by George P:

An intelligent & professional practitioner of the hot rodding arts, who is also a hydraulic engineer from the aviation industry, claims cavitation and leakage have been the issues with the 351C lubrication system all along. Others have intuitively hinted at the issue without labeling the problem as cavitation. I found the diagnosis compelling, so I consulted a couple of hydraulic engineers I know from my career in industry; after looking into the situation they fully agreed with the diagnosis, as though it was rather matter of fact. One commented "of course the tappets are going to cavitate at high speed".

I guess I don't read well anymore? I thought the issue was with oil pump cavitation? There's even a video illustrating it?

You wrote cavitation hadn't manifested itself as a problem with the 351C, you didn't really specify oil pump cavitation. I was focused on the issue of cavitation as a whole. I realize this may be new information to you Doug. Since lifter cavitation is the problem that most impacts the 351C I figured you'd be able to relate better if I used that as an example. If that muddies the issue for you I apologize. Yes cavitation is a problem at both the pump and the lifters.

quote:

Originally posted by George P:
On the subject of oil pumps, I can show you Ford literature from the 1960s recommending 3/4" ID for the oil pump suction line of a high performance motor, yet the largest suction line you can screw into a 351C oil pump has an ID of 5/8". As Homer Simpson would say ... DOH!

That's interesting information George.

It doesn't sound like much to go from 5/8" to 3/4" but that small change in size would actually result in almost 50 percent reduction in resistance to the inflowing oil. A considerable improvement to alleviate possible pump cavitation.

I do say possible cavitation because as i said earlier you can't see caviation unless you had xray vision, and it is hard to hear in a engine, the castings are too massive and the engine makes too much noise, you can only imagine it based on experience of what similar systems of similar design have been know to do in other circumstances. The experience of the hydraulic engineers is paramount.

I do agree with you that the lifter bore issue is a far worse problem than the oil pump and i think if a motor is being built up from scratch that is the way to go.

I was looking at this with the perspective of what can be done to a motor that is in a car and does not at this stage require a rebuild but could benefit from simple bolt on modifications eg: while the sump is off changing the stock connecting rod nuts perhaps look into the oil pump and sump for possible improvements ??

I agree a high volume pump is not desirable in the 351c and likely to make things worse.

But a larger inlet to any pump makes sense in any application whether it is a oil pump in a engine or a hydraulic pump or a fuel pump. Like the ports in the cylinder heads the inlet needs to be bigger than the exhaust/outlet.

Most things are made to a price or for ease of manufacture or simply designed to be "good enough" it is rare that no improvement can possibly be made to a item or system and subtle improvements are made to every other aspect of the 351c often without a moments thought. I don't understand why the oil pump should be thought of as "untouchable" especially when it is a bolt on item and easily changed out.



Best regards to everyone on the forum