0W20 load bearing capability in race block

[JAG]

Originally Posted By: Shannow
Your engineer is spot on about bearing exit temperature being way higher then bulk...

Expect some heat (no pun intended) on the issue, as there are those on this board who "don't believe" such engineering realities.

I know of one such loud board member who doesn't believe it. The guy needs to be corrected more frequently than we have time to do it.

 

[bigt61]

I road raced SBC engines for 20 years and 10lbs of OP per 1000 rpm was always the guideline. Oil temp was always measured coming out of the block before the cooler. Oil aeration is a big problem in high HP applications in road racing - I used a dry sump effectively after learning the hard (expensive) way.

 

[jrustles]

Originally Posted By: Belgian1979
Meanwhile I've been asking an engineer about this. It's not bulk oil temps that are the determining factor in this. It's the bearing exit temp which is. this is around 300°F. Viscosity is a lot lower then and too low for the 0W20 with regards to the bearing clearance. So from a technical point of view the 0W20 is a no go in a chevy with the bearing clearances involved. 30wt is about the lowest limit.

I was in search for an oil pressure problem but meanwhile I received the pump graph and everything points to a bypass being overworked. I'm going towards an external bypass exiting to the pan.


To play a little devil's advocate here, I'd put money on bearing exit temps paling in comparison to under-piston temps/ring temperatures. I'm curious about what your engineer friend says about that. Not only are the piston/rings in contact with a large, heat-liberating chemical reaction (bearing heat source is friction only) but the transfer of that piston heat to the cylinder wall all happens across the tiny contact patch of the rings. With bearing heat corresponding to friction, they rely on the cooling effect of flowing oil; the faster oil can be replaced in the bearing (side leakage), the less heat per volume of oil pumped through shall accept. Lucky for the bearing, as the piston rings can't say that they get same treatment of constant oil flow. The low vis oil can spend less time in 'peril' in a bearing, side leakage is greater in turn cooling the bearing more effectively. SBCs have rather decent journal sizes, so I don't think breach of the hydrodynamic wedge would happen as easily as say, a small Honda B-series journal. By keeping the bulk temps low, the entrance temperature to the bearings (and other lube points) is correspondingly lower. The 20 oil at a lower operating temperature effectively pumps like a higher (30) would at a higher temperature. So long as bulk temps don't spike, which is risky, then there really shouldn't be a problem but that is dancing on a blades edge. I personally need to have a margin of error built in, and again, that would most likely preclude 20 grade in this engine. But there are always two sides to consider.

With the HV oil pump, you'll always have proper displacement to move a 20 adequately through the engine. While I might not be recommending it, let's just face facts. There are always two sides to consider. I generally don't use HV pumps unless: I'm using grades thinner oil, clearances are increased, both. Having a HV pump otherwise creates problems like you're describing; wasting energy just bypassing oil.

Originally Posted By: bigt61
I road raced SBC engines for 20 years and 10lbs of OP per 1000 rpm was always the guideline. Oil temp was always measured coming out of the block before the cooler. Oil aeration is a big problem in high HP applications in road racing - I used a dry sump effectively after learning the hard (expensive) way.

Aeration is a concern for sure. If you're going to dump your bypass directly into a wet-sump oil pan, this could entrain air into the oil directly around the pickup tube. That could be bad. One last note about low viscosity oils to this point, is that they generally release air much quicker

 

[CATERHAM]

Originally Posted By: jrustles
Originally Posted By: Belgian1979

Aeration is a concern for sure. If you're going to dump your bypass directly into a wet-sump oil pan, this could entrain air into the oil directly around the pickup tube. That could be bad. One last note about low viscosity oils to this point, is that they generally release air much quicker

Not to mention when the oil is up to temperature the oil pump should not be in by-pass mode at all anyway. If it is the oil your running is too heavy.

 

[jrustles]

Originally Posted By: CATERHAM

Not to mention when the oil is up to temperature the oil pump should not be in by-pass mode at all anyway. If it is the oil your running is too heavy.


The only working oil pump not going operating bypass at the mid-top of the rev range is one pumping air. OP says he's running a high volume unit anyway, which exasperates the issue at hand- it will probably begin bypassing just off idle. Oil being at operating temperature moderately raises the RPM that the bypass begins to operate, and with heavier oils, that RPM is quite low. CAT's if you really think a bypass shouldn't be opened under normal conditions then I'd pay you upwards of 10bucks to mechanically disable your bypass valve, fill your engine with operating temperature TGMO 0W20, and bounce off the limiter. Just stand clear of the oil filter, is all I ask

 

[A_Harman]

Originally Posted By: Belgian1979
I was in search for an oil pressure problem but meanwhile I received the pump graph and everything points to a bypass being overworked. I'm going towards an external bypass exiting to the pan.


I agree with bmod305's comment on the previous page. Go back to the standard volume oil pump. Why bother putting the external bypass to the pan with the high volume pump? This just wastes energy and aerates the oil. Leave the oil in the pan until it is definitely needed. The more residence time the oil has in the pan, the more air it is able to release.

 

[CATERHAM]

Originally Posted By: jrustles
Originally Posted By: CATERHAM

Not to mention when the oil is up to temperature the oil pump should not be in by-pass mode at all anyway. If it is the oil your running is too heavy.


The only working oil pump not going operating bypass at the mid-top of the rev range is one pumping air. OP says he's running a high volume unit anyway, which exasperates the issue at hand- it will probably begin bypassing just off idle. Oil being at operating temperature moderately raises the RPM that the bypass begins to operate, and with heavier oils, that RPM is quite low. CAT's if you really think a bypass shouldn't be opened under normal conditions then I'd pay you upwards of 10bucks to mechanically disable your bypass valve, fill your engine with operating temperature TGMO 0W20, and bounce off the limiter. Just stand clear of the oil filter, is all I ask

You've lost me.
The by-pass on my Porsche set at nominally 108 psi. My Caterham is at 93 psi. A track buddies Z-06 is 80 psi.
Running TGMO 0W-20 in my Caterham at maximum rev's with 95C oil temp's, OP is around 65 psi.
Running the spec' oil the Porsche and Corvette, as in all cars I know of, will have maximum oil pressure significantly below the the by-pass point at normal hot operating temp's.

 

[CATERHAM]

I appreciate that many American V8 oil pumps have low by-pass settings of 60-65 psi but you should still not be in by-pass at normal hot operating temp's; it's counter-productive to do so.
Running a light 30wt oil you should be below by-pass at 90-95C oil temp's.

 

[Shannow]

Originally Posted By: jrustles
Originally Posted By: Belgian1979
Meanwhile I've been asking an engineer about this. It's not bulk oil temps that are the determining factor in this. It's the bearing exit temp which is. this is around 300°F. Viscosity is a lot lower then and too low for the 0W20 with regards to the bearing clearance. So from a technical point of view the 0W20 is a no go in a chevy with the bearing clearances involved. 30wt is about the lowest limit.

I was in search for an oil pressure problem but meanwhile I received the pump graph and everything points to a bypass being overworked. I'm going towards an external bypass exiting to the pan.


To play a little devil's advocate here, I'd put money on bearing exit temps paling in comparison to under-piston temps/ring temperatures. I'm curious about what your engineer friend says about that.


I'm interested in what the oil in contact with the underside of the piston is lubricating at the point it reaches these temperatures.

Engineer in question was talking about oil temperatures in an operational part of an engine where it's specifically the oil's viscosity that is doing the lubrication.

 

[jrustles]

Originally Posted By: CATERHAM
Originally Posted By: jrustles
Originally Posted By: CATERHAM

Not to mention when the oil is up to temperature the oil pump should not be in by-pass mode at all anyway. If it is the oil your running is too heavy.


The only working oil pump not going operating bypass at the mid-top of the rev range is one pumping air. OP says he's running a high volume unit anyway, which exasperates the issue at hand- it will probably begin bypassing just off idle. Oil being at operating temperature moderately raises the RPM that the bypass begins to operate, and with heavier oils, that RPM is quite low. CAT's if you really think a bypass shouldn't be opened under normal conditions then I'd pay you upwards of 10bucks to mechanically disable your bypass valve, fill your engine with operating temperature TGMO 0W20, and bounce off the limiter. Just stand clear of the oil filter, is all I ask

You've lost me.
The by-pass on my Porsche set at nominally 108 psi. My Caterham is at 93 psi. A track buddies Z-06 is 80 psi.
Running TGMO 0W-20 in my Caterham at maximum rev's with 95C oil temp's, OP is around 65 psi.
Running the spec' oil the Porsche and Corvette, as in all cars I know of, will have maximum oil pressure significantly below the the by-pass point at normal hot operating temp's.


The Porsche may be a little different than the SBC (and many other cars). 108psi is just a tad higher than most other vehicles on the road (50-64 psi) If we're talking about cars like Porsches, then you're right. An SBC is a little different. SBC with HV pump, mucho differento- lower bypass spring pressure, higher volume.

My KLZE is actually similar to your CATERHAM, I've been running Honda 0w20 in it and testing maximum pressures; I too top out around 65psi. Bypass spec is 80psi. The thing is, in the last third of the RPM range (5500+), pressure's stable @65 (hot). Imagine that?

Regular cars bypass a lot of the time. Example - A Toyota 4 cylinder with yet a shimmed bypass spring stabilized oil pressure at around 4800rpm (80psi) hot on 5w20. Caveat-it was the only S-engine equipped with a higher volume pump and it was overdriven. Camry original parts.

The Mazda F-engines had the following specs:
1,000 RPM 21-36 psi
3,000 RPM 44-58 psi
Oil Pump Relief Pressure 43-57 psi
(hot values). 3000+RPM and it's bypassing HOT.

So I'm just saying man, one absolutely cannot assert that an oil is 'too thick' because there is bypassing occurring during hot operation.


I would also like to share a story of repeatedly spun bearings, cross drilled cranks and 50 grade oil. What happens in the end is not at all what you thought

 

[jrustles]

Originally Posted By: Shannow


I'm interested in what the oil in contact with the underside of the piston is lubricating at the point it reaches these temperatures.

Engineer in question was talking about oil temperatures in an operational part of an engine where it's specifically the oil's viscosity that is doing the lubrication.


Point taken, Not to disregard piston pin and ring lubrication, but that's not the issue. If a bearing is overheating, there is another issue at play. I have seen this first hand. Built engine, cross-drilled crankshaft to improve bearing lubrication, running 50 grade repeatedly spinning bearings. He could not figure it out for the life of him why. There should be plenty of viscosity. On the third rebuild, he was suggested to drop a grade. Appetite for bearings suddenly vanished. Who knew?

I really respect and appreciate engineers, but we must not read more into what they're saying than they are. I think the point he was trying to make was 'bearing exit temperatures' should be a consideration, not "all bearing oil exit temps are around 300 degrees". He offered a rough ballpark figure to illustrate the point that bearing temps can surprise you. And I totally agree about local temperature deviations vs bulk temps. I've raised the point myself in previous posts.

We can still generalize that adequately-sized, moderately-loaded, high speed bearings fare best with the lowest viscosity oil allowable, and vice versa. So long as it's not completely breaking down from temperatures which is more likely at the ring TBH, and not in the bearing, especially a bearing being washed with more oil. I just don't see 20grade endangering a bearing in your common, naturally aspirated gasoline engine. Definitely not one that's been spec'ed for 5w30 since 5w30 existed. 5w30s (generally) has only recently been shear stable, otherwise millions of other V8s for decades have been running well on sheared out 5w30 of the past.

To make a determination on whether bearing temps are too high for the oil selection, we would need several data points that we don't have and cannot casually obtain. Bearing concerns wouldn't be the reason that I wouldn't run a 20grade in the SBC in question, IMO again it would be the camshaft. A solid 30 grade should be all that engine needs.

 

[CATERHAM]

Originally Posted By: jrustles

My KLZE is actually similar to your CATERHAM, I've been running Honda 0w20 in it and testing maximum pressures; I too top out around 65psi. Bypass spec is 80psi. The thing is, in the last third of the RPM range (5500+), pressure's stable @65 (hot). Imagine that?

So I'm just saying man, one absolutely cannot assert that an oil is 'too thick' because there is bypassing occurring during hot operation.


It's not unusual as in your Honda example for the oil pressure reading to rise quickly with rpm to a certain point and then the rate of OP increase with rpm continue at a much lower rate.
That doesn't mean you're in by-pass.
When the oil is cold you have no problem reaching your 80 psi by-pass point and if you ran a heavier oil your maximum OP level would be higher than the 65 psi(hot) you're seeing on Honda 0W-20. Run a 50wt oil and you would always be seeing 80 psi(hot) at high rev's.
If you installed an oil temp' gauge, running well into by-pass on an overly heavy oil driven under maximum load conditions such as lapping on a race track will allow oil temp's to rise noticeably due to the reduced oil flow vs a lighter oil that's not operating in by-pass.

 

[Shannow]

Originally Posted By: jrustles

I really respect and appreciate engineers, but we must not read more into what they're saying than they are. I think the point he was trying to make was 'bearing exit temperatures' should be a consideration, not "all bearing oil exit temps are around 300 degrees". He offered a rough ballpark figure to illustrate the point that bearing temps can surprise you. And I totally agree about local temperature deviations vs bulk temps.


The point is, and I've made it many times is that the temperature rise across a bearing can be 40C, and this means that the operational temperature, and thus the viscosity within the bearing is way lower than the bulk oil temperature would dictate...it's not an oil stability issue, it's operational viscosity, and bulk oil temps aren't much value in the calculation.

 

[CATERHAM]

Originally Posted By: Shannow
Originally Posted By: jrustles

I really respect and appreciate engineers, but we must not read more into what they're saying than they are. I think the point he was trying to make was 'bearing exit temperatures' should be a consideration, not "all bearing oil exit temps are around 300 degrees". He offered a rough ballpark figure to illustrate the point that bearing temps can surprise you. And I totally agree about local temperature deviations vs bulk temps.


The point is, and I've made it many times is that the temperature rise across a bearing can be 40C, and this means that the operational temperature, and thus the viscosity within the bearing is way lower than the bulk oil temperature would dictate...it's not an oil stability issue, it's operational viscosity, and bulk oil temps aren't much value in the calculation.

Shannow I would love to be convinced by you on this but I'm not.
With oil flow rates as high as 12 gallons a minute through an engine, that's the entire 4qt sump in 5 seconds, but bulk oil temp's aren't rising more than a fraction of a degree.

Secondly, bulk sump oil temp's is a reference point. An oil pressure gauge reading itself will reflect the average viscosity in the bearings whatever it is. My oil temp' gauge stopped working recently but from experience I could still accurately determine my bulk oil sump temp's with in a couple of degrees from my OP gauge.

 

[jrustles]

Originally Posted By: Shannow
Originally Posted By: jrustles

I really respect and appreciate engineers, but we must not read more into what they're saying than they are. I think the point he was trying to make was 'bearing exit temperatures' should be a consideration, not "all bearing oil exit temps are around 300 degrees". He offered a rough ballpark figure to illustrate the point that bearing temps can surprise you. And I totally agree about local temperature deviations vs bulk temps.


The point is, and I've made it many times is that the temperature rise across a bearing can be 40C, and this means that the operational temperature, and thus the viscosity within the bearing is way lower than the bulk oil temperature would dictate...it's not an oil stability issue, it's operational viscosity, and bulk oil temps aren't much value in the calculation.


I agree with that. And there is plenty to consider here ie. the source of heat in the bearing to begin with. That alone will vary wildly based load, speed, oil flow, and sure the bulk oil temperature too (cooler oil can accept more heat before a viscosity-related hydrodynamic breakdown).

Originally Posted By: CATERHAM

It's not unusual as in your Honda example for the oil pressure reading to rise quickly with rpm to a certain point and then the rate of OP increase with rpm continue at a much lower rate.
That doesn't mean you're in by-pass.


Doesn't it, though? The volume of oil being pumped is increasing in a near-linear fashion, the demand is virtually constant, yet the pressure plateaus in a non-linear manner. Something is beginning to leak pressure, right? If a bypass valve 'off it's seat' by 1mm leaks 3GPM@11cSt@65psi, it can leak 5GPM@7cSt@65psi (figures for example) at the same spring resistance (bypass orifice size). Of course, with a thicker oil, the bypass will need to be off it's seat moreto leak 5GPM@65psi, but the spring rate is constant, and so a higher backpressure is needed and will be seen to relieve the same required displacement. If this is the specified grade then that will put your OP right to spec. Anything thinner and your bypass operates on a different scale. Therefore I hypothesize that using oils thinner than specified can change the maximum seen oil pressure to lower than the maximum 'bypass' pressure specified in the shop manual, despite still operating at a higher leakage/pressure ratio. Does that make sense?

 

[Shannow]

Originally Posted By: jrustles
I agree with that. And there is plenty to consider here ie. the source of heat in the bearing to begin with.


Where do you think the heat rise across a bearing comes from ?

 

[Shannow]

Have posted this link before, and it shows where in an engine the frictional losses occur.

http://www.ricardo.com/Documents/Downloa...anceEngines.pdf

The bearing oil temperature rise is caused by the work that the engine does against the oil, pretty well summarised in the article. Convert the BMEP readings to watts, based on enginer metrics, and you are laughing.

 

[A_Harman]

Originally Posted By: Shannow
Originally Posted By: jrustles
I agree with that. And there is plenty to consider here ie. the source of heat in the bearing to begin with.


Where do you think the heat rise across a bearing comes from ?


Bearing load X coefficient of friction X bearing surface speed

The real joker in this deck is coeficient of friction. If there is oil present in the load zone with sufficient film thickness, coeff of friction will be very low, <.01. But if the oil viscosity drops to the point where the film thickness is less than the composite roughness of the bearing and journal, friction will increase, and so will the temperature of the oil leaving the bearing.

 

[Belgian1979]

This is the pump graph with approximatly the same spring in. Apparently it starts to drop off at 5000 rpm and is what i'm seeing.

Not sure what causes it. However I did notice that going from 10W40 to a 5W30 caused less (!) OP drop (only 5psi vs 15-20). I'm thinking that the pump is cavitating and the lower wt went easier into the inlet of the pump.

 

[jrustles]

Belgian, thank you for posting that. We finally have some data

This chart illustrates my point regarding the operation of the bypass. The test is performed with the required fixed orifice size to achieve 70psi at 4000 engine RPM (given that the pump itself is driven 2:1) on 5w30- at what I can only assume is to operating temperature? 70@4000rpm on the suggested viscosity is a pretty standard condition, nothing outrageous. You'll notice pump output is completely linear before about 1900 crankshaft RPM. That line corresponds perfectly to the pump's displacement output at those RPMs. The bypass valve is on it's seat. Over 1900RPM, the bypass begins to operate. Yes, nineteen-hundred RPM. Flow at the output of the pump begins to plateau, until 6000RPM where FLOW finally reaches it. You'll notice a blip on the graph at exactly 6000RPM. The bypass valve is being effected to it's specified fully-open point (not considering the secondary bypass design, which can open up even more, but without a progressive bleed control). At this RPM,6000, with the standard viscosity and clearances, is where given "bypass pressure specification" seen in manuals should match the PSIG. You'll notice 6000RPM is a far cry from where this graph clearly shows the bypass begin to function.

Belgian, with regard to the "sudden drop" of PSI using higher viscosity oil, which is not seen using a lower viscosity oil, is something a few people are noticing and it's not vehicle specific. Cavitation is one possibility, though it real cavitation is rare IMO. There should be no reason a pickup tube and screen can't flow 10GPM of 40grade, unless there is contamination or a severe design flaw. I've mentioned this to another recent poster with nearly identical concern. I pointed the finger to the bypass design, which is the culprit IMO, but not a flaw. Given that the bypass is a dynamic, progressive orifice, and that it's bleed rate is proportional to its position in the bore, which is determined by the spring rate x backpressure, it regulates pressure but only relative to the fluid's viscosity. Some pump designs use what I'd call a secondary bypass channel, beyond the linear, progressive increase of leakage used in normal bypass operation. When the valve cylinder get's pushed beyond the normal 'primary' range, a second orifice with a much larger, 'uncontrolled' leakage capacity opens up. This is a smart thing to do IMO as it allows wrecklessly high RPMs on cold and/or viscous oil without excessive internal pressure spikes that can lead to damage. I hypothesize that you're entering the secondary bypass range (where leakage is much less controlled, a true bypass mode) when using the 10W40. This is exactly an appropriate time where CATERHAM could tell you that your oil (10w40) is too thick and he would be absolutely right.