As a sidenote about the curve, you can even see the induced resonances on the output flow from the plunger & spring riding on the backpressure
0W20 load bearing capability in race block
- Thread starter Belgian1979
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Thank you, jrustles, for that interesting analysis of the pump data.
I'm still figuring out what do about this issue. There are only a couple of solutions (dry sump aside which is very impractical on this car) that I see right now and there are the following :
- using a 0W20 which would reduce the pump using the bypass as more oil would be pumped through the engine, but as already stated I fear that it might be too thin for the bearings.
- going back to the std pump with the same size inlet which does pump about 25% less volume and therefor would solicitate the bypass less. If the engine however needs a higher volume, then I would see it dropping of again.
- mounting an external bypass with a somewhat lower setting than the internal spring, with a significantly bigger return to the sump (-10).
The last solution can be done rather simple and even without pulling the pan. But there is a possible issue with this solution. It would mean that all of the oil the pump can put out has to pass through the inlet. What I want to say is that if for example the pump pumps 40 gpm at high rpm but the engine only consumes 10 gpm that the difference of 30 gpm would bypass normally internal in the pump. The inlet would therefor only have to flow 10 gpm extra, which would keep the inlet pressure drop and thus cavitation in check. If I go to the external bypass where the bypass is connected to the sump, the internal bypass would be not functioning anymore and the pump would have to pump effectively 40 gpm through the inlet. This would mean a significant pressure drop in the inlet possible creating cavitation.
Via an online calculation I made a simulation. At the current maximum flow it seems that I have less than 1/2 psi pressure drop in the inlet tube. If I have to flow the full amount it would drop approximatly 2,4 psi, which is a lot. I also noticed the linear line before 2000 engine rpm and based on that I estimated that on 6000 rpm the pump is pumping around 50 gpm. So effectively pumping 41 gpm too much. The question is how much more the engine will flow at high rpm. Some say the amount of flow remains the same, some say it goes up because of the lifters moving up and down more, the crankshaft rotating causing centrifugal forces etc etc.
There is a possible third additional solution I could introduce to the external bypass and that is a fixed orifice in the return line to the sump. This would reduce the amount the line can flow and by drilling the orifice bigger (or making it smaller it could be corrected to adjust the return via this line and keep the Original bypass kicking in, thereby reducing the inlet pressure drop that could be created.
PS : others have reasoned that due to the engine needing more gmp flow at high rpm the oil pump never reaches the bypass setting....if this is true that would mean the inlet is restricted.
Oh and Jrestless I didn't quite understand what you said about the secondary bypass. I only have 1 bypass as far as I know.
Thanks for sharing your knowledge.
- using a 0W20 which would reduce the pump using the bypass as more oil would be pumped through the engine, but as already stated I fear that it might be too thin for the bearings.
- going back to the std pump with the same size inlet which does pump about 25% less volume and therefor would solicitate the bypass less. If the engine however needs a higher volume, then I would see it dropping of again.
- mounting an external bypass with a somewhat lower setting than the internal spring, with a significantly bigger return to the sump (-10).
The last solution can be done rather simple and even without pulling the pan. But there is a possible issue with this solution. It would mean that all of the oil the pump can put out has to pass through the inlet. What I want to say is that if for example the pump pumps 40 gpm at high rpm but the engine only consumes 10 gpm that the difference of 30 gpm would bypass normally internal in the pump. The inlet would therefor only have to flow 10 gpm extra, which would keep the inlet pressure drop and thus cavitation in check. If I go to the external bypass where the bypass is connected to the sump, the internal bypass would be not functioning anymore and the pump would have to pump effectively 40 gpm through the inlet. This would mean a significant pressure drop in the inlet possible creating cavitation.
Via an online calculation I made a simulation. At the current maximum flow it seems that I have less than 1/2 psi pressure drop in the inlet tube. If I have to flow the full amount it would drop approximatly 2,4 psi, which is a lot. I also noticed the linear line before 2000 engine rpm and based on that I estimated that on 6000 rpm the pump is pumping around 50 gpm. So effectively pumping 41 gpm too much. The question is how much more the engine will flow at high rpm. Some say the amount of flow remains the same, some say it goes up because of the lifters moving up and down more, the crankshaft rotating causing centrifugal forces etc etc.
There is a possible third additional solution I could introduce to the external bypass and that is a fixed orifice in the return line to the sump. This would reduce the amount the line can flow and by drilling the orifice bigger (or making it smaller it could be corrected to adjust the return via this line and keep the Original bypass kicking in, thereby reducing the inlet pressure drop that could be created.
PS : others have reasoned that due to the engine needing more gmp flow at high rpm the oil pump never reaches the bypass setting....if this is true that would mean the inlet is restricted.
Oh and Jrestless I didn't quite understand what you said about the secondary bypass. I only have 1 bypass as far as I know.
Thanks for sharing your knowledge.
Bypass is bad, as it's just shifting pressurised oil and making heat. (if 25% of your oil is going through the bypass, then that's 25% of your pump power that is doing nothing but heating the oil), so I wouldn't be going to another external bypass really...I wouldn't use an oil that provided "high flow" if it wasn't doing lubrication in the meantime.
Bypass says that your engine doesn't need the volume for the most part.
Note that the chart provided earlier is volume versus revs, not pressure.
Mellings offers an anti cavitation model if you want such...this article suggests that pump output on an SBC flatlines at 5500RPM (like your chart)
http://www.enginebuildermag.com/Article/59172/oil_pump_technology.aspx
As you increase revs above that point, the bearings will be pulling in more oil than the pump can deliver (and maintain pressure), which could be why your pressure is dropping...not indicative of not enough oil getting there.
Bypass says that your engine doesn't need the volume for the most part.
Note that the chart provided earlier is volume versus revs, not pressure.
Mellings offers an anti cavitation model if you want such...this article suggests that pump output on an SBC flatlines at 5500RPM (like your chart)
http://www.enginebuildermag.com/Article/59172/oil_pump_technology.aspx
As you increase revs above that point, the bearings will be pulling in more oil than the pump can deliver (and maintain pressure), which could be why your pressure is dropping...not indicative of not enough oil getting there.
The big question remains whether the engine uses more oil volume at higher rpms or not. If that is the case, I agree that the pump output would fall short at 5500. In essence the clearances don't grow to such an extent that they would play a role. Other effect however may play a role. If the engine needs more oil flow at higher rpm, a smaller pump would certainly not do the trick.
What's especially intriguing is that the pressure was more stable when going to a lower wt. If pump output would be to small, it would have dropped more than with a heavier wt, which is why I assume other aspects might have a bigger influence here and the flow that the engine needs at higher rpm hasn't increased substantially but the flow throug the bearing did, basically bleeding off more of the bypass and putting the pump less on the bypass.
BTW : although I didn't like it, I performed a (very short) test where I put the engine at higher rpm's with a cold engine and it did exactly the same thing as with a heavier wt oil.
I'm however not sure I have a full view on how all the different aspects play a role.
What's especially intriguing is that the pressure was more stable when going to a lower wt. If pump output would be to small, it would have dropped more than with a heavier wt, which is why I assume other aspects might have a bigger influence here and the flow that the engine needs at higher rpm hasn't increased substantially but the flow throug the bearing did, basically bleeding off more of the bypass and putting the pump less on the bypass.
BTW : although I didn't like it, I performed a (very short) test where I put the engine at higher rpm's with a cold engine and it did exactly the same thing as with a heavier wt oil.
I'm however not sure I have a full view on how all the different aspects play a role.
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Bearings have a pressure profile that's caused by hydrodynamics...
In places, the pressure can actually drop below ambient, and suck their own oil into the bearing (I've seen a couple of big ones that draw 1-2psi at speed)
They act as a "pump" taking oil from the high clearance area, dragging it into the low clearance area, providing "lift" and lubrication, and squeezing oil out the sides.
If you are supplying oil (say), at the point (w) in the picture above, at a rate greater than the bearing needs, it will be shifted out the side, creating excessive leakage (and really doing what a bypass would likely be doing)
If the ability of the bearing to move oil is increasing with revs (yes), and the pump can't provide the excess leakage in the area (w), then the "backpressure" will be reduced and the pressure, which in and of itself does no lubrication, will drop.
Doesn't mean that the bearings are "starved" or at risk.
In places, the pressure can actually drop below ambient, and suck their own oil into the bearing (I've seen a couple of big ones that draw 1-2psi at speed)
They act as a "pump" taking oil from the high clearance area, dragging it into the low clearance area, providing "lift" and lubrication, and squeezing oil out the sides.
If you are supplying oil (say), at the point (w) in the picture above, at a rate greater than the bearing needs, it will be shifted out the side, creating excessive leakage (and really doing what a bypass would likely be doing)
If the ability of the bearing to move oil is increasing with revs (yes), and the pump can't provide the excess leakage in the area (w), then the "backpressure" will be reduced and the pressure, which in and of itself does no lubrication, will drop.
Doesn't mean that the bearings are "starved" or at risk.
Ok, Shannow, thanks for that explication, but I would still like to know why the pressure drop was reduced running the thinner oil vs the 10W40. I would have expected it to drop more somehow.
I'm going further on 0W20. It's known that hydrodynamic oil wedge is dependant on relative speed between the moving parts, oil viscosity, load and clearance.
Clearance is fixed here, so that cannot be altered. A thinner oil would reduce the hydrodynamic effect. Load is mostly dependant on rpm, where the higher the rpm the most load will be in the bearing, exactly the point where i'm seeing the pressure drop, which is also the point where the relative speed between the parts is highest. If I use the thinner 0W20 I would assume the bearings would be at risk the most at lower rpm, but that is the point where the pressure produced by this pump is highest. Therefor I would assume (!) that it's feasable to run 0W20 in this oil.
I'm not sure but I'm thinking it might get the pressure up on the higher rpms where I want them.
Just some food for thought and I would say, keep the arguments coming.
I'm going further on 0W20. It's known that hydrodynamic oil wedge is dependant on relative speed between the moving parts, oil viscosity, load and clearance.
Clearance is fixed here, so that cannot be altered. A thinner oil would reduce the hydrodynamic effect. Load is mostly dependant on rpm, where the higher the rpm the most load will be in the bearing, exactly the point where i'm seeing the pressure drop, which is also the point where the relative speed between the parts is highest. If I use the thinner 0W20 I would assume the bearings would be at risk the most at lower rpm, but that is the point where the pressure produced by this pump is highest. Therefor I would assume (!) that it's feasable to run 0W20 in this oil.
I'm not sure but I'm thinking it might get the pressure up on the higher rpms where I want them.
Just some food for thought and I would say, keep the arguments coming.
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You have to remember that you are not measuring pressure at the bearings or in the system, you are measuring back pressure.
Also, unless you're talking about some different chart, the chart you posted has flow, not back pressure.
Also, unless you're talking about some different chart, the chart you posted has flow, not back pressure.
Originally Posted By: KrisZ
You have to remember that you are not measuring pressure at the bearings or in the system, you are measuring back pressure.
Also, unless you're talking about some different chart, the chart you posted has flow, not back pressure.
It's true, but always remember that the flow curve is congruent with backpressure. The pressure would rise at the same rate as flow does in the chart, and would plateau exactly as flow does. It's just that for the purpose of flow testing, a pressure scale would not be useful.
Quote:
BTW : although I didn't like it, I performed a (very short) test where I put the engine at higher rpm's with a cold engine and it did exactly the same thing as with a heavier wt oil.
Yes. Exactly the behavior I'd expect.
Originally Posted By: Shannow
Bearings have a pressure profile that's caused by hydrodynamics...
In places, the pressure can actually drop below ambient, and suck their own oil into the bearing (I've seen a couple of big ones that draw 1-2psi at speed)
They act as a "pump" taking oil from the high clearance area, dragging it into the low clearance area, providing "lift" and lubrication, and squeezing oil out the sides.
If you are supplying oil (say), at the point (w) in the picture above, at a rate greater than the bearing needs, it will be shifted out the side, creating excessive leakage (and really doing what a bypass would likely be doing)
If the ability of the bearing to move oil is increasing with revs (yes), and the pump can't provide the excess leakage in the area (w), then the "backpressure" will be reduced and the pressure, which in and of itself does no lubrication, will drop.
Doesn't mean that the bearings are "starved" or at risk.
Interesting perspective Shan's, thanks for posting. Certainly some bearing behavior we should consider.
You have to remember that you are not measuring pressure at the bearings or in the system, you are measuring back pressure.
Also, unless you're talking about some different chart, the chart you posted has flow, not back pressure.
It's true, but always remember that the flow curve is congruent with backpressure. The pressure would rise at the same rate as flow does in the chart, and would plateau exactly as flow does. It's just that for the purpose of flow testing, a pressure scale would not be useful.
Quote:
BTW : although I didn't like it, I performed a (very short) test where I put the engine at higher rpm's with a cold engine and it did exactly the same thing as with a heavier wt oil.
Yes. Exactly the behavior I'd expect.
Originally Posted By: Shannow
Bearings have a pressure profile that's caused by hydrodynamics...
In places, the pressure can actually drop below ambient, and suck their own oil into the bearing (I've seen a couple of big ones that draw 1-2psi at speed)
They act as a "pump" taking oil from the high clearance area, dragging it into the low clearance area, providing "lift" and lubrication, and squeezing oil out the sides.
If you are supplying oil (say), at the point (w) in the picture above, at a rate greater than the bearing needs, it will be shifted out the side, creating excessive leakage (and really doing what a bypass would likely be doing)
If the ability of the bearing to move oil is increasing with revs (yes), and the pump can't provide the excess leakage in the area (w), then the "backpressure" will be reduced and the pressure, which in and of itself does no lubrication, will drop.
Doesn't mean that the bearings are "starved" or at risk.
Interesting perspective Shan's, thanks for posting. Certainly some bearing behavior we should consider.
Ok, but what would be the route to take from here.
MolaKule
Staff member
Ok, I admit that I am late to the "pressure" party but here are my suggestions:
1. Get a pan with baffles to make sure the pickup has sufficient oil to draw from. Increase oil sump volume with a larger sump pan or increase oil volume by 1/2 quart over full mark.
2. Keep the same HF oilpump and use a racing oil 5W20. That oll should have the highest HTHS you can find, about >= 1000 ppm of phos/zinc, > 200 ppm of moly, and the highest VI.
I am in agreement with Shannow that the leakage around the bearings is beneficial in that the more leakage, the greater oil flow will be carrying more heat that is conducted away from the bearing.
3. Use an oil cooler in front of the radiator to moderate the engine's oil temperature. This will keep the viscosity more stable.
I base this on Cameron's first order equation of frictional forces within bearings:
Ff = pi^2 X u X Db^2 X Lb X N)/h'
where;
u is oil viscosity,
Db is bearing diameter,
Lb is bearing length,
N is RPM or shaft rotational speed
h' is mean radial clearance.
1. Get a pan with baffles to make sure the pickup has sufficient oil to draw from. Increase oil sump volume with a larger sump pan or increase oil volume by 1/2 quart over full mark.
2. Keep the same HF oilpump and use a racing oil 5W20. That oll should have the highest HTHS you can find, about >= 1000 ppm of phos/zinc, > 200 ppm of moly, and the highest VI.
I am in agreement with Shannow that the leakage around the bearings is beneficial in that the more leakage, the greater oil flow will be carrying more heat that is conducted away from the bearing.
3. Use an oil cooler in front of the radiator to moderate the engine's oil temperature. This will keep the viscosity more stable.
I base this on Cameron's first order equation of frictional forces within bearings:
Ff = pi^2 X u X Db^2 X Lb X N)/h'
where;
u is oil viscosity,
Db is bearing diameter,
Lb is bearing length,
N is RPM or shaft rotational speed
h' is mean radial clearance.
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I already use a fully baffled, windagetrayed, scrapered etc pan with 7 qrts. I already 'overfilled' with the adverse effect it reduced pressure. I underfilled it as well, to only see that it didn't have any effect.
As for the oil cooler, it's already in place and it employs an electric fan, which is even regulated at 175-180°F.
I've been reading up on the hydrodynamic wedge forming in bearings, but most info I read there is that a lower viscosity has the tendency to reduce the wedge significantly.
As stated, I talked to an engineer that said that at the bearing with a temp of 302°F the viscosity of 0W20 (or 5W20 for that matter) is 3.9cst.
I'm not sure how to make the calculation to see if i'm in the boundary lubrication with that or still in the hydrodynamic lubrication area of the graphs.
As for the journals : mains : 2.450", rod journals 2.100". Bearing clearances on the mains .0025"-.0027" and for the rods .0023".
If anyone could make this calculation with the above info, many thanks.
As for the oil cooler, it's already in place and it employs an electric fan, which is even regulated at 175-180°F.
I've been reading up on the hydrodynamic wedge forming in bearings, but most info I read there is that a lower viscosity has the tendency to reduce the wedge significantly.
As stated, I talked to an engineer that said that at the bearing with a temp of 302°F the viscosity of 0W20 (or 5W20 for that matter) is 3.9cst.
I'm not sure how to make the calculation to see if i'm in the boundary lubrication with that or still in the hydrodynamic lubrication area of the graphs.
As for the journals : mains : 2.450", rod journals 2.100". Bearing clearances on the mains .0025"-.0027" and for the rods .0023".
If anyone could make this calculation with the above info, many thanks.
Belgian1979, you haven't said how you use your car?
Is your car in the States or Europe?
Is it for street use or racing?
You might find the following link to Joe Gibbs Driven useful.
For a strictly race use engine they recommend their XP1 5W-20 race oil for V8 engines with clearances under 0.0025" and bulk sump oil temp's of 180F-240F:
http://s11.n205.n222.n216.static.myhostcenter.com/products/syntheticracingoil/xp1.html
Is your car in the States or Europe?
Is it for street use or racing?
You might find the following link to Joe Gibbs Driven useful.
For a strictly race use engine they recommend their XP1 5W-20 race oil for V8 engines with clearances under 0.0025" and bulk sump oil temp's of 180F-240F:
http://s11.n205.n222.n216.static.myhostcenter.com/products/syntheticracingoil/xp1.html
Europe, Belgium, close to Germany. I do occassional do German autobahn at higher speeds. For the rest high performance street use. Car has a short ratio rear so need rpm. Engine is made to turn up to 7500 rpm.
Seeing the recommend below .0025 and a race blend for 9500 rpm. This is probably a Nascar race blend. They use some pretty strikt clearances.
I think the 0W20 is out of question on this engine. Have to search for a problem on the pump. Not sure what route to take. Might end up with dry sump. Personally I would have thought the HV pump would have been good to 8000 or so.
Seeing the recommend below .0025 and a race blend for 9500 rpm. This is probably a Nascar race blend. They use some pretty strikt clearances.
I think the 0W20 is out of question on this engine. Have to search for a problem on the pump. Not sure what route to take. Might end up with dry sump. Personally I would have thought the HV pump would have been good to 8000 or so.
MolaKule
Staff member
Quote:
I've been reading up on the hydrodynamic wedge forming in bearings, but most info I read there is that a lower viscosity has the tendency to reduce the wedge significantly.
As stated, I talked to an engineer that said that at the bearing with a temp of 302°F the viscosity of 0W20 (or 5W20 for that matter) is 3.9cst.
Are you referring to a "static" wedge where the journal/bearing sucks in the oil. Or are you referring to a conventional pressurized and drilled journal where there is pressurized oil flowing down the journal and exiting the drilled journal holes to the bearings?
In terms of fluid thermodynamics, the cooler oil, say at the bulk oil temperature (and depending on how you have the oil cooling circuit plumbed), will enter the bearing and pick up journal/bearing heat and exit via the side leakage at a higher temp but carrying the heat away back to the bulk oil where it will be cooled down again.
I've been reading up on the hydrodynamic wedge forming in bearings, but most info I read there is that a lower viscosity has the tendency to reduce the wedge significantly.
As stated, I talked to an engineer that said that at the bearing with a temp of 302°F the viscosity of 0W20 (or 5W20 for that matter) is 3.9cst.
Are you referring to a "static" wedge where the journal/bearing sucks in the oil. Or are you referring to a conventional pressurized and drilled journal where there is pressurized oil flowing down the journal and exiting the drilled journal holes to the bearings?
In terms of fluid thermodynamics, the cooler oil, say at the bulk oil temperature (and depending on how you have the oil cooling circuit plumbed), will enter the bearing and pick up journal/bearing heat and exit via the side leakage at a higher temp but carrying the heat away back to the bulk oil where it will be cooled down again.
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I'm not sure but I remember it being all about pressure fed bearings. The other ones were mentioned as wick fed....
I'm to chick to throw in 5W20. The info on the engine states 5W30 as the thinnest, so....
I also have a lead on parts to make an external bypass because I also feel Jrestless has a point there. However I fear it might make the pump inlet at risk of inducing cavitation....or I would have to restrict the external bypass with a fixed orifice. Lots of things to consider.
I'm to chick to throw in 5W20. The info on the engine states 5W30 as the thinnest, so....
I also have a lead on parts to make an external bypass because I also feel Jrestless has a point there. However I fear it might make the pump inlet at risk of inducing cavitation....or I would have to restrict the external bypass with a fixed orifice. Lots of things to consider.
Originally Posted By: Belgian1979
I'm not sure but I remember it being all about pressure fed bearings. The other ones were mentioned as wick fed....
I'm to chick to throw in 5W20. The info on the engine states 5W30 as the thinnest, so....
I also have a lead on parts to make an external bypass because I also feel Jrestless has a point there. However I fear it might make the pump inlet at risk of inducing cavitation....or I would have to restrict the external bypass with a fixed orifice. Lots of things to consider.
For a street driven car you are way over thinking this unless you simply enjoy talking engine design.
Since the engine builder has suggested 5W-30 (is that an A5/B5 or A3/B4 30wt oil?) then that's what you start with.
Forget about messing with the by-pass valve, as your not likely going to be running in by-pass mode at higher rev's anyway. Do you know the by-pass spec' of your oil pump?
Put a few thousand miles on the car. Get familiar with the bulk oil temp's and oil pressure characteristics of your engine and report back.
I'm not sure but I remember it being all about pressure fed bearings. The other ones were mentioned as wick fed....
I'm to chick to throw in 5W20. The info on the engine states 5W30 as the thinnest, so....
I also have a lead on parts to make an external bypass because I also feel Jrestless has a point there. However I fear it might make the pump inlet at risk of inducing cavitation....or I would have to restrict the external bypass with a fixed orifice. Lots of things to consider.
For a street driven car you are way over thinking this unless you simply enjoy talking engine design.
Since the engine builder has suggested 5W-30 (is that an A5/B5 or A3/B4 30wt oil?) then that's what you start with.
Forget about messing with the by-pass valve, as your not likely going to be running in by-pass mode at higher rev's anyway. Do you know the by-pass spec' of your oil pump?
Put a few thousand miles on the car. Get familiar with the bulk oil temp's and oil pressure characteristics of your engine and report back.
Originally Posted By: Belgian1979
Ok, but what would be the route to take from here.
Why not 5w30 and sleep easy? There is no concern for the bearings in your application IMO, even on a 20grade. HV pump further enables superior flow with 20/30 grade, and less pressure drop throughout the oil galleries- meaning less pressure drop between the pump outlet and the actual orifice. That is a very real concern and I think you should consider the following
[small digression]
Oil flow is paramount. Let's discuss what happens to oil after the oil pump with different viscosities. (starts boring, but leads somewhere
) All oil reaching the rod bearings must travel through a labyrinth of oil passages within the engine. Right off the pump outlet, the oil enters the first half of the main gallery. Being a well-sized artery, we expect a minimal pressure drop. Next, oil is led into the filter, depending on design, we'll see a moderate pressure drop- and an oil cooler will again cause a pressure drop. After the oil filter, is where most OP gauge sender units are located. The pressure you see at this point has already dropped via the filter (and cooler if equipped). So it should be noteworthy that there will always be a discrepancy between the pressures that the bypass valve sees, and your OP gauge.
Also, again another reason that I explicitly implicate the bypass as the cause of your secondary pressure drop, and not cavitation, is simply due to the fact that there is so much resistance to flow on the supply end, that it would be almost ludicrous to think that the pickup tube/screen could be more of an impedance than the filter, cooler, and oil galleries. Trust me, the delivery side is not accepting more oil than the pickup can supply! Especially not a high viscosity oil like the 40, which would flow even less to the delivery side, and even more through the bypass...... causing it to enter a higher relief zone in the upper RPMs where you notice the PSIG drop.
But back on topic, after the filter, oil enters the main gallery- the manifold of which all things are fed. Depending on engine design, under-piston oil squirters are fed directly off of the main gallery. As this can severely drop pressure to all other feeds, they are sometimes valved by springs, where they open only above a certain PSI. I'm not sure if SBCs are commonly equipped with piston oil squirters. Anyway, other feeds directly off the main gallery are to the head(s), to the VVT, to the turbo, and to the main bearings.
Now for the good stuff, let's focus on the bearings. The mains get fed right off the main gallery, pressure drop is minimal. What about the rods? Well, the only way they can be fed is through the crankshaft. The oil passages in the crankshaft are a pressure drop nightmare. Not only does the feed have to enter a constantly rotating orifice at the main bearing, which is already leaking volume from it's clearance, but the already pressure-dropped feed into the crankshaft via the mains must again find it's way through small, angularly drilled passages within the crank. Getting to the rod bearing orifice, we now have seen the ultimate pressure drop in an engine, compared to what we see on the gauge. Pressure/flow still adequate, but if we're going to obsess, 'adequate' won't do it
High viscosity oils make that pressure drop worse, like 40s, 50s will suffer the utmost pressure drop at the bearing. Counterintuitive to what most would think, a higher viscosity oil can easily increase bearing temperatures with a std clearance. Not only from the increased molecular friction that must be overcome, liberating only heat, but the flow rate across the bearing will be much reduced, again inhibiting cooling. And pressure/flow was already impeded before it entered the crank! NOW we can talk about 300 degree bearing exit temperatures- because with impaired bearing cooling, and increased drag, 300 degreeF exits would be easily obtained . I can promise you that with even a 20 grade, you will not see bearing temperatures in that range, precluding the supply oil from breaking down. Further to the point, SBC main and rod journals are well-sized, and a longer bearing has a higher surface speed, at the same crankshaft RPM, and higher bearing speeds enable a stable hydrodynamic wedge on low vis oil, comparable to a shorter bearing with a higher vis oil.
Notes:
-there is the effect of "slinging" within the crank that would contribute to oil flow. In reality, the contribution is insignificant and cannot compensate for prior flow deficiencies.
-short bearings/low RPMs (low bearing surface speed) and extreme loading does necessitate the usage of high viscosity such as an engine with diesel-like crankpin forces (turbo) combined with small sized bearings (such as a highly boosted Honda B-engine for instance with a 45mm crankpin).
[/small digression]
tl;dr
Pros-Cons to viscosity
Low Vis
Pros:
-better flow/supply, enabling better cooling and less stagnation in high stress areas
-less molecular friction, less heat generated
-less pressure/flow drop at the end of delivery system (rod bearings), again enabling better cooling
-less useless work (bypassing)
Cons:
-less durable film strength in localized areas
-less thermal stability, cannot stand being stagnated in high stress areas (which is counterintuitive to it's greater flow)
High Vis:
Pros:
-thicker film strength; stronger hydrodynamic wedge relative to force applied.
-greater thermal stability, can withstand stagnation in high stress areas better, (despite it's resistance to flow exasperating this condition in the first place)
Cons:
-resistance to flow reduces, well, flow. greater pressure/flow drop at end of delivery system (rod bearing)
-less flow means more bypassing, useless work robbing horsepower, liberating heat
-more molecular friction (drag) within the bearing; increased thermal load for no reason, both increaselocal and bulk temperatures
Belgian, I'm not going to tell you exactly what to do, I hope you can make the decision on your own, based on knowledge.
Ok, but what would be the route to take from here.
Why not 5w30 and sleep easy? There is no concern for the bearings in your application IMO, even on a 20grade. HV pump further enables superior flow with 20/30 grade, and less pressure drop throughout the oil galleries- meaning less pressure drop between the pump outlet and the actual orifice. That is a very real concern and I think you should consider the following
[small digression]
Oil flow is paramount. Let's discuss what happens to oil after the oil pump with different viscosities. (starts boring, but leads somewhere
Also, again another reason that I explicitly implicate the bypass as the cause of your secondary pressure drop, and not cavitation, is simply due to the fact that there is so much resistance to flow on the supply end, that it would be almost ludicrous to think that the pickup tube/screen could be more of an impedance than the filter, cooler, and oil galleries. Trust me, the delivery side is not accepting more oil than the pickup can supply! Especially not a high viscosity oil like the 40, which would flow even less to the delivery side, and even more through the bypass...... causing it to enter a higher relief zone in the upper RPMs where you notice the PSIG drop.
But back on topic, after the filter, oil enters the main gallery- the manifold of which all things are fed. Depending on engine design, under-piston oil squirters are fed directly off of the main gallery. As this can severely drop pressure to all other feeds, they are sometimes valved by springs, where they open only above a certain PSI. I'm not sure if SBCs are commonly equipped with piston oil squirters. Anyway, other feeds directly off the main gallery are to the head(s), to the VVT, to the turbo, and to the main bearings.
Now for the good stuff, let's focus on the bearings. The mains get fed right off the main gallery, pressure drop is minimal. What about the rods? Well, the only way they can be fed is through the crankshaft. The oil passages in the crankshaft are a pressure drop nightmare. Not only does the feed have to enter a constantly rotating orifice at the main bearing, which is already leaking volume from it's clearance, but the already pressure-dropped feed into the crankshaft via the mains must again find it's way through small, angularly drilled passages within the crank. Getting to the rod bearing orifice, we now have seen the ultimate pressure drop in an engine, compared to what we see on the gauge. Pressure/flow still adequate, but if we're going to obsess, 'adequate' won't do it
Notes:
-there is the effect of "slinging" within the crank that would contribute to oil flow. In reality, the contribution is insignificant and cannot compensate for prior flow deficiencies.
-short bearings/low RPMs (low bearing surface speed) and extreme loading does necessitate the usage of high viscosity such as an engine with diesel-like crankpin forces (turbo) combined with small sized bearings (such as a highly boosted Honda B-engine for instance with a 45mm crankpin).
[/small digression]
tl;dr
Pros-Cons to viscosity
Low Vis
Pros:
-better flow/supply, enabling better cooling and less stagnation in high stress areas
-less molecular friction, less heat generated
-less pressure/flow drop at the end of delivery system (rod bearings), again enabling better cooling
-less useless work (bypassing)
Cons:
-less durable film strength in localized areas
-less thermal stability, cannot stand being stagnated in high stress areas (which is counterintuitive to it's greater flow)
High Vis:
Pros:
-thicker film strength; stronger hydrodynamic wedge relative to force applied.
-greater thermal stability, can withstand stagnation in high stress areas better, (despite it's resistance to flow exasperating this condition in the first place)
Cons:
-resistance to flow reduces, well, flow. greater pressure/flow drop at end of delivery system (rod bearing)
-less flow means more bypassing, useless work robbing horsepower, liberating heat
-more molecular friction (drag) within the bearing; increased thermal load for no reason, both increaselocal and bulk temperatures
Belgian, I'm not going to tell you exactly what to do, I hope you can make the decision on your own, based on knowledge.
Originally Posted By: Belgian1979
I think the 0W20 is out of question on this engine. Have to search for a problem on the pump. Not sure what route to take. Might end up with dry sump. Personally I would have thought the HV pump would have been good to 8000 or so.
That might be a long search my friend, because IMO the pump is working as it was designed
In reality, even with the gauge pressure drop, lubrication should still be adequate, but it would be smart to eliminate it altogether by simply using a lower viscosity!!
Dry sump? maybe a bit extreme. If you absolutely had to prevent the bypass from opening to full flow on 40grade just for psychological comfort, then you would simply increase spring tension/shim. Nothing more.
But the pump will experience higher internal pressure, and will drag more on the engine.
Originally Posted By: Belgian1979
I'm not sure but I remember it being all about pressure fed bearings. The other ones were mentioned as wick fed....
I'm to chick to throw in 5W20. The info on the engine states 5W30 as the thinnest, so....
I also have a lead on parts to make an external bypass because I also feel Jrestless has a point there. However I fear it might make the pump inlet at risk of inducing cavitation....or I would have to restrict the external bypass with a fixed orifice. Lots of things to consider.
Listen to the math guys and play with some calculations. You might just end up putting yourself at ease
I think the 0W20 is out of question on this engine. Have to search for a problem on the pump. Not sure what route to take. Might end up with dry sump. Personally I would have thought the HV pump would have been good to 8000 or so.
That might be a long search my friend, because IMO the pump is working as it was designed
Dry sump? maybe a bit extreme. If you absolutely had to prevent the bypass from opening to full flow on 40grade just for psychological comfort, then you would simply increase spring tension/shim. Nothing more.
Originally Posted By: Belgian1979
I'm not sure but I remember it being all about pressure fed bearings. The other ones were mentioned as wick fed....
I'm to chick to throw in 5W20. The info on the engine states 5W30 as the thinnest, so....
I also have a lead on parts to make an external bypass because I also feel Jrestless has a point there. However I fear it might make the pump inlet at risk of inducing cavitation....or I would have to restrict the external bypass with a fixed orifice. Lots of things to consider.
Listen to the math guys and play with some calculations. You might just end up putting yourself at ease
Originally Posted By: MolaKule
I base this on Cameron's first order equation of frictional forces within bearings:
Ff = pi^2 X u X Db^2 X Lb X N)/h'
where;
u is oil viscosity,
Db is bearing diameter,
Lb is bearing length,
N is RPM or shaft rotational speed
h' is mean radial clearance.
What is this equation calculating? Torque loss in a bearing as a function of bearing dimensions and viscosity? There is a right parenthesis in there, where should the left parenthesis be? (Hate to be nitpicking on that.) Also, is the pi^2 term correct?
I base this on Cameron's first order equation of frictional forces within bearings:
Ff = pi^2 X u X Db^2 X Lb X N)/h'
where;
u is oil viscosity,
Db is bearing diameter,
Lb is bearing length,
N is RPM or shaft rotational speed
h' is mean radial clearance.
What is this equation calculating? Torque loss in a bearing as a function of bearing dimensions and viscosity? There is a right parenthesis in there, where should the left parenthesis be? (Hate to be nitpicking on that.) Also, is the pi^2 term correct?
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