Shane661
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posted August 14, 2009 08:58 AM
 Edited By: Shane661 on 14 Aug 2009 17:00
Again: Crankcase/OIl Pressure?
I know we covered some of this a while back.
I am still trying to figure out something regarding vaccum inside of the crankcase and how it may cause the oil light to flicker, etc.. It has been stated elsewhere that the reason the oil light will flicker with a crankcase mod is that the pressure is switch is calibrated for operation with atmospheric pressure+ within the crankcase. Now, I am not very smart about these things...so I would like to get some opions on that.
Also, if that is the case...isn't the key measurement the absolute pressure differential between the crankcase pressure and the oil pressure? If you are pulling a vacuum within the crankcase, would your oil pressure in PSIG be correspondingly lower?
Any insights would be appreciated. This is the type of stuff that I wake up in the middle of the night thinking about. 
Shane
  
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kawasakijockey
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posted August 14, 2009 09:20 AM
Yes it would Shane. I proved it to a friend last week on his car by putting a Shopvac to his oil filler cap for a couple seconds. He watched the oil pressure go from 40 psi to 30 immediately he said.
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Shane661
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posted August 14, 2009 01:27 PM
quote:
Yes it would Shane. I proved it to a friend last week on his car by putting a Shopvac to his oil filler cap for a couple seconds. He watched the oil pressure go from 40 psi to 30 immediately he said.
That is what I suspected. Probably the best data would be to log oil pressure and crankcase pressure together.
My feeling, then, is that the idiot light is really not a valid indicator when running lowered crankcase pressure.
Perhaps someone will dispute this, so I'll keep an eye on this thread.
Shane
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tcchin
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posted August 14, 2009 02:24 PM
Edited By: tcchin on 14 Aug 2009 22:26
So what is happening to the oil pressure in the bearing journals? Isn't that the key question? If that pressure value is significantly lower, like shopvac lower, then you could have oil starvation issues. I'd log both oil and crankcase pressures, but I don't think I'd necessarily add one to the other to derive some estimate for what the bearing journals are seeing. If there isn't enough pressure to keep the idiot light sensor open, then there probably isn't enough to keep the crankshaft afloat either.
Shane - what kind of vacuum device are you using to purge your crankcase? Is it capable of evacuating the crankcase to below-ambient pressures during normal operating conditions?
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NOX
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posted August 14, 2009 02:48 PM
I run the mod, and have just normal oil pressue.......
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Shane661
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posted August 14, 2009 02:59 PM
Edited By: Shane661 on 14 Aug 2009 23:01
quote:
So what is happening to the oil pressure in the bearing journals? Isn't that the key question? If that pressure value is significantly lower, like shopvac lower, then you could have oil starvation issues. I'd log both oil and crankcase pressures, but I don't think I'd necessarily add one to the other to derive some estimate for what the bearing journals are seeing. If there isn't enough pressure to keep the idiot light sensor open, then there probably isn't enough to keep the crankshaft afloat either.
Shane - what kind of vacuum device are you using to purge your crankcase? Is it capable of evacuating the crankcase to below-ambient pressures during normal operating conditions?
If I were doing anything it would simply be using the kleen reed valves to suck the pressure from the crankcase. I don't want to start a debate on the merits of this; I am just trying to determine why some people see the oil light flicker when doing this mod, and get an idea of how crankcase and oil pressures are related.
Regarding the oil pressure issues:
What I'm saying is, the gauge pressure is one thing...but isn't it relative to one atmosphere of pressure? So, if you are operating in an environment of less than one atmosphere you would expect the gauge pressure to be less. However, the differential between crankcase and oil pressure would seem to be more pertinent.
Basically, suppose:
Crankcase pressure = 14
Oil Pressure = 50
Differential = 36
Crankcase pressure = 0
Oil pressure = 36
Differential = 36
Wouldn't both instances presumably supply the same volume and relative pressure of oil to the journals?
Shane
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kawasakijockey
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posted August 14, 2009 03:11 PM
You would have to use a vaccum pump to get a significantly lower oil pressure reading. The venturi type mods will pull some minor negatives but nothing like a pump would. Some engines are dynoed where they make the most power and acceptable oil pressures when setting up vaccum pumps. Too much vaccum will cause ring expansion weakness and that means a significant loss of power and lubricity at the rings. Now you see that it is not just a oil pressure problem you have to worry about. There is an adjustable vent on the pump type set-ups to get it just where you need it. On one nitrous car we used a smog pump. Worked extremely well for what it was it seemed.
____________
Get on the shortbus boys 'cause its time to get schooled.
2007 ZX-14
1.38 60ft
9.03 @ 149mph
8.95 @153 small shot n2o
8.68 @160mph 5lbs boost
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kawasakijockey
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posted August 14, 2009 03:15 PM
Edited By: kawasakijockey on 14 Aug 2009 23:18
You have to have a diff. for the oil pump to actually pull oil up, which is actually being pushed up by positive crankcase pressure from a physics stand point. I think I am getting in over my head and will bow out now...
____________
Get on the shortbus boys 'cause its time to get schooled.
2007 ZX-14
1.38 60ft
9.03 @ 149mph
8.95 @153 small shot n2o
8.68 @160mph 5lbs boost
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Shane661
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posted August 14, 2009 03:17 PM
Edited By: Shane661 on 14 Aug 2009 23:18
quote:
You would have to use a vaccum pump to get a significantly lower oil pressure reading. The venturi type mods will pull some minor negatives but nothing like a pump would. Some engines are dynoed where they make the most power and acceptable oil pressures when setting up vaccum pumps. Too much vaccum will cause ring expansion weakness and that means a significant loss of power and lubricity at the rings. Now you see that it is not just a oil pressure problem you have to worry about. There is an adjustable vent on the pump type set-ups to get it just where you need it. On one nitrous car we used a smog pump. Worked extremely well for what it was it seemed.
I have read about some of concerns (such as loss of windage-induced lubrication) with high vacuum systems. I know that the mod we are talking about will not produce anywhere near those vacuum levels.
I can't discount what others report about the idiot light, however. I want to know why it occurs, even without seemingly significant levels of vacuum.
Shane
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kawasakijockey
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posted August 14, 2009 03:19 PM
My post above yours might explain that some. Maybe??
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2007 ZX-14
1.38 60ft
9.03 @ 149mph
8.95 @153 small shot n2o
8.68 @160mph 5lbs boost
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Shane661
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posted August 14, 2009 03:21 PM
Edited By: Shane661 on 14 Aug 2009 23:21
quote:
You have to have a diff. for the oil pump to actually pull oil up, which is actually being pushed up by positive crankcase pressure from a physics stand point. I think I am getting in over my head and will bow out now...
But once the pump is primed, I believe it will do the work. Due to the pump design, it cannot help but pump.
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kawasakijockey
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posted August 14, 2009 03:26 PM
Edited By: kawasakijockey on 14 Aug 2009 23:26
quote:
quote:
You have to have a diff. for the oil pump to actually pull oil up, which is actually being pushed up by positive crankcase pressure from a physics stand point. I think I am getting in over my head and will bow out now...
But once the pump is primed, I believe it will do the work. Due to the pump design, it cannot help but pump.
To a point. Positive pressure is still necessary to feed a pump that is upstairs. If the pump was submerged in the sump then you would be 100% correct.
Does anyone know the pressure that makes the oil light come on?
____________
Get on the shortbus boys 'cause its time to get schooled.
2007 ZX-14
1.38 60ft
9.03 @ 149mph
8.95 @153 small shot n2o
8.68 @160mph 5lbs boost
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Shane661
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posted August 14, 2009 03:32 PM
quote:
quote:
quote:
You have to have a diff. for the oil pump to actually pull oil up, which is actually being pushed up by positive crankcase pressure from a physics stand point. I think I am getting in over my head and will bow out now...
But once the pump is primed, I believe it will do the work. Due to the pump design, it cannot help but pump.
To a point. Positive pressure is still necessary to feed a pump that is upstairs. If the pump was submerged in the sump then you would be 100% correct.
Does anyone know the pressure that makes the oil light come on?
Positive pressure in relation to what is created on the suction side of the pump...right?
I imagine I can avoid this worry by simply installing a dry sump oiling system.
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tcchin
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posted August 14, 2009 03:43 PM
I'm not debating merits. I agree that oil pressure is equal to the pressure drop across the pump, which is independent of internal crankcase pressure. And I agree that the oil pressure sending unit is probably referencing atmospheric pressure. However, I don't know how the oil will behave in reduced internal pressure conditions. Cavitation and foaming are issues that have greater influence once the internal pressure drops, so even though the relative pressure is the same across the pump, the oil's resistance to foaming might be compromised. That's why suspension components are gas-charged, as I'm sure you know.
I don't think a Kleen air valve system can flow enough volume to cause any significant change in crankcase pressure, though...
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Shane661
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posted August 14, 2009 03:50 PM
Edited By: Shane661 on 14 Aug 2009 23:50
I saw it posted on another site that someone (remember Motorhead, anyone?) did some testing and found that the mod could create 15"+ of vacuum during high rpm deceleration. True or not, it was claimed.
I don't know too much about suspension components, but what you are saying makes sense.
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kawasakijockey
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posted August 14, 2009 05:01 PM
quote:
I'm not debating merits. I agree that oil pressure is equal to the pressure drop across the pump, which is independent of internal crankcase pressure. And I agree that the oil pressure sending unit is probably referencing atmospheric pressure. However, I don't know how the oil will behave in reduced internal pressure conditions. Cavitation and foaming are issues that have greater influence once the internal pressure drops, so even though the relative pressure is the same across the pump, the oil's resistance to foaming might be compromised. That's why suspension components are gas-charged, as I'm sure you know.
I don't think a Kleen air valve system can flow enough volume to cause any significant change in crankcase pressure, though...
Cavitation and foaming are very good points. And air bubble expanded before the pump by negative pressure then compressed by the pump and expanded at discharge, hmmm. ..maybe something to it all.
____________
Get on the shortbus boys 'cause its time to get schooled.
2007 ZX-14
1.38 60ft
9.03 @ 149mph
8.95 @153 small shot n2o
8.68 @160mph 5lbs boost
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BrooklynNYZX12
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posted August 14, 2009 06:10 PM
I think this is being over analyzed,it's certainly strange that a crankcase mod would cause an oil light to flicker but too much pressure in the crankcase would cause a leak condition,wouldn't it?Something along the lines of an engine with too much blow by ,which is crankcase pressure on the positive side,crankcase pressure on a negative side like on a typical exhaust/evac system should never cause a light to flicker...how could the engine exhaust venturi effect cause that?Most evac systems have the one way type of anti-backfire valve,could the absence of that valve cause the light to flicker?Maybe the engine guys like Tcchin or Y2K or DMeyer can explain that.A real vacuum pump type of crankcase scavenging systems true potential is really only realized when used in conjunction w/ a gas ported type of piston along with a low tension ring.I am just trying to understand this while trying not to overthink,the lights on because the pressure in the engine is low....jus my .02
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Shane661
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posted August 15, 2009 03:58 AM
Edited By: Shane661 on 15 Aug 2009 12:14
I know it seems like a lot of analysis for what is likely potentially a very, very minute gain in power.
But, ask youself this: How much hp does it take to go from 211.974 to 212.0 MPH?
If I could determine the safety of the mod, and get confirmation of the cause of the low oil pressure light, then I would feel free to waste my 30 minutes on the potential of .33 HP.
It sounds as though nobody has done this mod and logged the results (with the exception of Motorhead, perhaps).
Shane
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entropy
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posted August 15, 2009 04:52 AM
way back when I had a FBG vac pump and it caused flickering of the oil light at idle and on decel at 1/4 mi. I lost a motor and figured the pump MIGHT have contributed.
These days I log oil pressure, and if i still had the pump I would simply look at the oil pressure logs and see what impact it has (if any).
No need to get tangled up in our theoretical shoelaces on this issue; log oil pressure and see directly.
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Y2KZX12R
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posted August 15, 2009 05:04 AM
Edited By: Y2KZX12R on 15 Aug 2009 13:15
BrooklynNYZX12 is exactly correct with this statement.
"A real vacuum pump type of crankcase scavenging systems true potential is really only realized when used in conjunction w/ a gas ported type of piston along with a low tension ring."
Yesterday I read this post and decided to gather a few of the shop Indians that are in the know on this stuff, Bill, Dino, Harold, and myself but Harold the dyno operator already had left for the races.
We discussed this in detail for 15 minutes and I gathered all of "what we do know" and "what we don't know". and everything else in between is speculation on our assumptions.
On the dyno, on a V8 road race engine we typically pull the crankcase down to 10" HG.
Drag race Big Blocks we typically pull down to 15" HG
An engine that is designed to use low tension rings will benefit from crankcase evacuation.
An engine that uses "regular" or "normal" rings will typically LOOSE power from crankcase evacuation.
Typically evacuation lowers the oil pressure that the sensor sees by a factor of approx. 1 to 1. In other words 15"HG of vacuum lowers oil pressure 15 psi. Now this is not exact and smaller engines like bike engines may be different. I'll have to find out if this is on a wet AND dry sump setup.
Gas ported pistons and evacuated crankcases wear the rings out faster. Some road-race engines wear the rings out in one race.
Assuming the ring package is thin low radial tension and designed for an evacuated crankcase, you need to pull a CONSTANT 10-15" min to realize the benefits.
We couldn't conclude why the oil pressure drop happens.
It could be the clearances in the "positive" displacement pump.
It could be that the lower pressure is micro-cavitation the suction into the pump. (un likely)
It could be a flow rate increase of total oil flow threw the system due to the lower pressure "sucking the oil past the rod and main bearings. (most likely)
But we have used flow meters on the oil system to monitor total flow from the output line of the pressure pump and haven't seen a change in total volume with and without an evacuated crankcase. I believe this was only done on the dry sump system. I'll find out.
Dry sump collection tanks are vented to atmosphere so there is ambient pressure above the supply pool of oil going to the pressure stage of the pump. Where as a wet sump has vacuum above the supply pool of oil to the pump.
So if the pressure drop is seen on both types of systems then one would have to conclude that its NOT an issue of pump supply. It must be an issue of increasing the flow (reducing restriction) after the pump. But we have seen no flow increase using a flow meter. But they may have only measured total flow with the flow meter on the dry sump engine and not the wet sump engines.
I'll find out if the pressure drop is seen on both evacuated wet and dry sump setups.
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BrooklynNYZX12
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posted August 15, 2009 06:57 AM
Jim am I understanding you correctly??...maybe oversimplifying this by assuming that 10-15hg of vacuum in the crankcase of any engine in theory now,can potentially pull the oil away from rod and main bearings?I am thinking that 10-15 hg is a pretty heavy pull..it starts to make sense...Would it be crazy to shim the pump spring to raise the oil pressure to off-set the 1 to 1 ratio of crankcase vacuum vs oil pressure?
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kawasakijockey
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posted August 15, 2009 07:12 AM
Or what we did on the last 421 small block, changed to a heavier viscocity. We did not see any power drop like you might see with these smaller engines though.
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Get on the shortbus boys 'cause its time to get schooled.
2007 ZX-14
1.38 60ft
9.03 @ 149mph
8.95 @153 small shot n2o
8.68 @160mph 5lbs boost
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Shane661
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posted August 15, 2009 07:17 AM
I guess my thought is that just because you have a lower PSIG in an evacuated engine, it does not absolutely mean that oiling is adversely affected. It just means that your gauge pressure is lower because it is using 1 atmosphere of pressure as it's reference.
Even more of interest, to me, is at what point you adversely impact ring sealing when using standard rings in an evacuated system.
Shane
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Y2KZX12R
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posted August 16, 2009 05:38 AM
Edited By: Y2KZX12R on 16 Aug 2009 13:53
quote:
Jim am I understanding you correctly??...maybe oversimplifying this by assuming that 10-15hg of vacuum in the crankcase of any engine in theory now,can potentially pull the oil away from rod and main bearings?
Were not sure on that. Were not sure exactly why the oil pressure drop at the sensor is seen. Could be.
quote:
Would it be crazy to shim the pump spring to raise the oil pressure to off-set the 1 to 1 ratio of crankcase vacuum vs oil pressure?
Shimming the oil pressure relief valve will not raise the oil pressure below about say 8000 rpm.
The only time it can raise the oil pressure is if the pressure that the valve sees is higher than the valve is set to open at. This doesn't occur until quite high rpms.
The only way to raise the oil pressure throughout the entire rpm range is to increase the pump volume per rotation or increase the resistance of the flow of oil throughout the engine.
Using a higher viscosity oil will show a higher pressure in the oil system but its because of a reduction of flow. This flow reduction may not be a good thing for sustained high RPM.
It can cause the crank and rods to run hotter because of the cooling reduction from the lower oil flow.
Technically the viscosity of the oil you use is determined by the flow rate of oil to the crank and rods. and the flow rate is determined by the rod and main bearing clearances.
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Y2KZX12R
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posted August 16, 2009 05:50 AM
quote:
I guess my thought is that just because you have a lower PSIG in an evacuated engine, it does not absolutely mean that oiling is adversely affected. It just means that your gauge pressure is lower because it is using 1 atmosphere of pressure as it's reference.
Even more of interest, to me, is at what point you adversely impact ring sealing when using standard rings in an evacuated system.
Shane
There is no guarantee that pulling 15" HG in the crank case of an engine that its going to make more power. It may make no difference or it may cause ring flutter at some rpms and not make a difference at others.
And then your results would only represent your combo with that ring and piston combo with that crosshatch and cylinder RA finish. We have MANY cylinder surface finishes we do for different applications.
You would have to do a dyno test with a real evacuation pump where you could change the crankcase vacuum levels to find this out.
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