2/6 rod bearing flow tests
02-29-2012, 04:29 PM
#16
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I'm working on a universal 928 oil pan design to keep oil in the tank & around the pick-up: once I get closer I'll share some photos & such. I have both an OB pan & 32v pan to measure from.
That article was great, nice to see an experiment put towards the theories. My only concern is that air bubbles travel pretty fast through water & I wouldn't expect the exact same through oil: bubbles would be tiny in a froth'd environment. More frothed oil isn't the answer: we gotta go back to solid anti-froth & starved pick-up ideas.
That article was great, nice to see an experiment put towards the theories. My only concern is that air bubbles travel pretty fast through water & I wouldn't expect the exact same through oil: bubbles would be tiny in a froth'd environment. More frothed oil isn't the answer: we gotta go back to solid anti-froth & starved pick-up ideas.
02-29-2012, 04:33 PM
#17
Race Director
Actually, I think the pick-up isn't important to the problem. I went with a later pickup because it has a screen. I also didn't like the look of the spring-loaded rubber pieces on the old pickups that I have. Getting stiff.
The IJ kit has specific features to keep oil in the sump. That's the problem: the oil leaves the sump under acceleration because it's shallow and in the front.
I do wonder about the RPM range used by the drivers of your car and with the auto transmission. Also, with the lower power (4.7 US, right?) it's not accelerating as hard as other 928s.
The IJ kit has specific features to keep oil in the sump. That's the problem: the oil leaves the sump under acceleration because it's shallow and in the front.
I do wonder about the RPM range used by the drivers of your car and with the auto transmission. Also, with the lower power (4.7 US, right?) it's not accelerating as hard as other 928s.
Wasn't your OB that had 2-6 failure an 82? So its HP is basically the same as mine.....215whp-256 torque is pretty strong considering a 20% loss of the automatic....
I do wonder why they put the sump in front....since keeping the pickup covered under braking isn't nearly as important as acceleration....must have been a space issue with the cross member....
02-29-2012, 06:44 PM
#19
Nordschleife Master
No. '80 Euro S. (and an '82 isn't an OB)
I used to let it rev to 6500 and downshift before corners. Now I shift at 6250 and downshift near the apex instead of while braking.
A lower RPM shift points makes a lot of difference.
A huge factor in engine longevity is driver style and the tracks the car is driven on. It's hard to quantify so it's not well included in comparisons of oil issue solutions.
I used to let it rev to 6500 and downshift before corners. Now I shift at 6250 and downshift near the apex instead of while braking.
A lower RPM shift points makes a lot of difference.
A huge factor in engine longevity is driver style and the tracks the car is driven on. It's hard to quantify so it's not well included in comparisons of oil issue solutions.
02-29-2012, 06:53 PM
#20
Nordschleife Master
I wonder whether the mains water pressure is high enough for a reasonable comparative test? The 928 oil pump pushes a huge amount of oil - and mains water is only usually 500-1500kPA or so depending on where. Someone needs to provide Bernard with a 10bar-capable water pump and bigger collection tanks for measuring flow.
The drilling of the hole to 2/6 and results on the second page are especially interesting. Some really good work there - but I wonder whether the dead-spots in the bubble entrainment/turbulence are located in the same places at higher pressures/speeds?
I also hope they manage to achieve more testing of modifications like deepening the intake tract for the 2/6 and 3/7 mains.
A great testing setup!
The drilling of the hole to 2/6 and results on the second page are especially interesting. Some really good work there - but I wonder whether the dead-spots in the bubble entrainment/turbulence are located in the same places at higher pressures/speeds?
I also hope they manage to achieve more testing of modifications like deepening the intake tract for the 2/6 and 3/7 mains.
A great testing setup!
03-01-2012, 10:01 AM
#21
Nordschleife Master
This reminds me of a guy who claimed to have solved the bearing problem by machining the cradle passages. Since that can't stop sucking in the foam, that approach must distribute it more evenly.
That'd increase life, I suppose.
That'd increase life, I suppose.
03-01-2012, 10:41 AM
#22
Three Wheelin'
I hypothesis that the reason for the low flow at 2/6 is a venturi effect from the high volume that sails past the entry of 2/6.
The aeration exasorbates the condition. Even by testing with the alternate drilled hole passage, they still didn't counter the venturi effect IMHO.
I don't know what others have done for machining the 'cradle' passage as a cure but I machine the main passage larger at the area around the 2/6 alley and the entry of the alley in such a way as to decrease the venturi effect.
03-01-2012, 10:56 AM
#23
Nordschleife Master
That's interesting.
What would be really effective is getting the aerated oil to go through the pressure relief valve and back to the pan. Since it's lighter it'll go to the top of a passage and towards the inside of bends. Perhaps there's another way to do it. Probably needs to be external.
Idea:
Increase the spring rate on the pressure relief valve and then put a normal pressure (7 bar?) relief on an oil-cooler line that prefers to shunt foamy oil back to the pan.
What would be really effective is getting the aerated oil to go through the pressure relief valve and back to the pan. Since it's lighter it'll go to the top of a passage and towards the inside of bends. Perhaps there's another way to do it. Probably needs to be external.
Idea:
Increase the spring rate on the pressure relief valve and then put a normal pressure (7 bar?) relief on an oil-cooler line that prefers to shunt foamy oil back to the pan.
03-01-2012, 12:45 PM
#24
Rennlist Member
Great find Erkka, Thanks!
Am I correct that the stock pressure-relief valve returns oil to the pump inlet rather than the pan?
I would think that aerated oil, with its lower density, would prefer the direct path through the pressure relief valve-- for the same reason it prefers the more direct path to the 2/6 journal. But instead of getting sent to the pan to de-aerate, it gets sent straight back to the pump to take another try at the bearings-- there is no path that lets the foam go anywhere, except to the bearings.
What would it take to change the pressure relief to return to the sump, instead of the pump inlet? An external relief valve is one choice, but could it be done by drilling another passage?
That's interesting.
What would be really effective is getting the aerated oil to go through the pressure relief valve and back to the pan. Since it's lighter it'll go to the top of a passage and towards the inside of bends. Perhaps there's another way to do it. Probably needs to be external.
Idea:
Increase the spring rate on the pressure relief valve and then put a normal pressure (7 bar?) relief on an oil-cooler line that prefers to shunt foamy oil back to the pan.
What would be really effective is getting the aerated oil to go through the pressure relief valve and back to the pan. Since it's lighter it'll go to the top of a passage and towards the inside of bends. Perhaps there's another way to do it. Probably needs to be external.
Idea:
Increase the spring rate on the pressure relief valve and then put a normal pressure (7 bar?) relief on an oil-cooler line that prefers to shunt foamy oil back to the pan.
I would think that aerated oil, with its lower density, would prefer the direct path through the pressure relief valve-- for the same reason it prefers the more direct path to the 2/6 journal. But instead of getting sent to the pan to de-aerate, it gets sent straight back to the pump to take another try at the bearings-- there is no path that lets the foam go anywhere, except to the bearings.
What would it take to change the pressure relief to return to the sump, instead of the pump inlet? An external relief valve is one choice, but could it be done by drilling another passage?
03-01-2012, 01:00 PM
#26
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The flow test shows that the thrust bearing & heads get considerably more oil then the other bearings. Didn't Louie's video test show that only one head is receiving too much oil, hence the limit the oil to the one head via the 944 restrictor? I'm just trying to get this small grey area of my knowledge filed properly.
I still think the best solution is merely to eliminate sump cavitation to remove the foaming entirely: hence a new pan/pickup design.
I still think the best solution is merely to eliminate sump cavitation to remove the foaming entirely: hence a new pan/pickup design.
03-01-2012, 01:10 PM
#27
Archive Gatekeeper
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At least on an engine sitting still on a dyno above 6000 rpm, the heads fill and blow liquid oil out of all four valve cover elbows (if so equipped) at exactly the same time. If adding in lateral g-forces ione way or another, then YMMV.
03-01-2012, 01:12 PM
#28
Race Director
The flow test shows that the thrust bearing & heads get considerably more oil then the other bearings. Didn't Louie's video test show that only one head is receiving too much oil, hence the limit the oil to the one head via the 944 restrictor? I'm just trying to get this small grey area of my knowledge filed properly.
I still think the best solution is merely to eliminate sump cavitation to remove the foaming entirely: hence a new pan/pickup design.
I still think the best solution is merely to eliminate sump cavitation to remove the foaming entirely: hence a new pan/pickup design.
1: Oil aeration.....this is huge....probably 90% of all the issues.....there are many reasons why the oil gets aerated...but reducing this will solve many oiling issues
2: Reduce oil to the heads which will reduces the chances of the heads filling up with oil at high rpm....which of course causes #1 once the oil level gets low enough....by capping the pressure-flow to the heads will increase the flow to the mains-rods....but with the recent cam damage I have seen from GT cam engines...I wonder if this is a good idea...
03-01-2012, 01:13 PM
#29
Nordschleife Master
The best solution is to not have air in the oil. I don't think that's actually feasible in a real-world engine. Very large dry sump tanks are not "real-world."
Dry sumping and windage control can reduce it to be negligible but even then if the more aerated oil could be separated out then it would be an improvement.
03-01-2012, 02:20 PM
#30
Nordschleife Master
I've been wondering about a vertical tube maybe 3" in diameter, oil from the sump goes in the side, top feeds the valve train in the heads, bottom feeds the bearings. I'm guessing bubbles in the oil would not be much of an issue in the heads.