Oil starvation problem at high rpm
10-29-2003, 02:16 PM
#61
Those are some very nice pics Martin! These are GREAT!
So your saying that that crank is now "cross drilled" as all of us refer to it? And there is additional chamges to make it the way the 928 cranks are "drilled"?
I do know that you also need to change the main bearings.
So your saying that that crank is now "cross drilled" as all of us refer to it? And there is additional chamges to make it the way the 928 cranks are "drilled"?
I do know that you also need to change the main bearings.
10-29-2003, 05:26 PM
#63
928 Collector
Rennlist Member
Rennlist Member
My experience with the subject is admittedly only mine, but I think there's more to 2/6 rod bearing failures than just what is goin on in the oil pan and crank or lower oiling passages in the block. I say this because I've seen Louie Ott's "holy cam covers" and their videos, where there is so much oil sloshing (not misting) up against the inside of the passenger's cam cover that it looks as if there's an oil pump spurting directly at it.
My 292rwhp/294rwft-lbs stock S4 engine (no-one knows why it's so strong) has never had any problems, except that under very hard cornering, and not even very high revs (I say above 3k) she drinks oil as if someone had inserted a straw into the sump and connected it to the throttle body for vacuum. I took note of oil pressure, and my oil level was perfect to start. Under high-G cornering I saw no oil pressure drop, though if I had, I bet I'd be throwing an engine away right about now. The little sucker tube in the throttle body was wet with fresh oil.
Louie killed his 2/6 bearings on-track, and I was there. His GT ingested oil exactly as mine did. I assume his starved the bearings as a result.
So -- I know there are those much more experienced and far smarter on this topic, but when you're pumping oil and gushing it toward the undersides of your cam covers, you cannot expect that oil to be available elsewhere. This is most definitely a Porsche design flaw.
The sad thing is, many of those who would solve the problem if they only pooled resources, have $$$$ motives (not necessarily bad) and therefore, we may never resolve this flaw, or even understand it properly. I've spent much time trying to think it through, and I'm intrigued by the notion that Porsche themselves did not understand the causes and possible resolution of the flaw. I note that most failures of which I've heard, occur during long sweeping LEFT-handers. OK, so the cam cover on that side spews oil into the intake, risking detonation and starvation of bearings etc. What about the driver's cam cover? Why did Porsche not put the "breathers" there? Could it be that German tracks turn clockwise, so that oil is forced in a direction under the cam cover that has no place for the oil to exit?
I've spent much time discussing the flaw with a NASCAR geek I know, who builds big block engines. He says that there is no way I could be describing the breather system in our engines properly, because if that were the case, we'd be looking at a closed system, with no air inlet. This is considered a meaningless system where you're not allowing fresh air to flow through the crankcase to vent blowby etc.
So -- what is the solution?? No idea. Maybe PCV and reroute. Ps: is it just me, or are those oil drainback holes in the heads teeeeny, and in exactly the wrong place?
My 292rwhp/294rwft-lbs stock S4 engine (no-one knows why it's so strong) has never had any problems, except that under very hard cornering, and not even very high revs (I say above 3k) she drinks oil as if someone had inserted a straw into the sump and connected it to the throttle body for vacuum. I took note of oil pressure, and my oil level was perfect to start. Under high-G cornering I saw no oil pressure drop, though if I had, I bet I'd be throwing an engine away right about now. The little sucker tube in the throttle body was wet with fresh oil.
Louie killed his 2/6 bearings on-track, and I was there. His GT ingested oil exactly as mine did. I assume his starved the bearings as a result.
So -- I know there are those much more experienced and far smarter on this topic, but when you're pumping oil and gushing it toward the undersides of your cam covers, you cannot expect that oil to be available elsewhere. This is most definitely a Porsche design flaw.
The sad thing is, many of those who would solve the problem if they only pooled resources, have $$$$ motives (not necessarily bad) and therefore, we may never resolve this flaw, or even understand it properly. I've spent much time trying to think it through, and I'm intrigued by the notion that Porsche themselves did not understand the causes and possible resolution of the flaw. I note that most failures of which I've heard, occur during long sweeping LEFT-handers. OK, so the cam cover on that side spews oil into the intake, risking detonation and starvation of bearings etc. What about the driver's cam cover? Why did Porsche not put the "breathers" there? Could it be that German tracks turn clockwise, so that oil is forced in a direction under the cam cover that has no place for the oil to exit?
I've spent much time discussing the flaw with a NASCAR geek I know, who builds big block engines. He says that there is no way I could be describing the breather system in our engines properly, because if that were the case, we'd be looking at a closed system, with no air inlet. This is considered a meaningless system where you're not allowing fresh air to flow through the crankcase to vent blowby etc.
So -- what is the solution?? No idea. Maybe PCV and reroute. Ps: is it just me, or are those oil drainback holes in the heads teeeeny, and in exactly the wrong place?
10-29-2003, 06:23 PM
#65
Nordschleife Master
Originally posted by M758
Once those pluged cavities fill with oil it does not mater where the hole is as the oil will flow out in any direction.
Once those pluged cavities fill with oil it does not mater where the hole is as the oil will flow out in any direction.
10-29-2003, 06:32 PM
#66
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928 v Chevy oilway drillings end on.
The 60 deg. before max load is stated in 'how to hotrod smallblock Chevys'
The 928's is 40 deg. in front of this & 160 deg. behind.
The 60 deg. before max load is stated in 'how to hotrod smallblock Chevys'
The 928's is 40 deg. in front of this & 160 deg. behind.
10-29-2003, 06:47 PM
#67
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Brendan
My 2nd pic. is of a stock crank & is cross drilled from the factory, they all are. So when others talk of getting the crank cross-drilled to cure the 2/6, what are they talking about ?
Doug
The Mercs at le Mans in the early '90s used 0-60 Castrol RS/Syntec striaght from the can as sold in the shops, the Jags at the same time used the same oil except it was modified to counter bore wash/fuel contamination
My 2nd pic. is of a stock crank & is cross drilled from the factory, they all are. So when others talk of getting the crank cross-drilled to cure the 2/6, what are they talking about ?
Doug
The Mercs at le Mans in the early '90s used 0-60 Castrol RS/Syntec striaght from the can as sold in the shops, the Jags at the same time used the same oil except it was modified to counter bore wash/fuel contamination
10-29-2003, 06:50 PM
#68
OKay, so is this how the 928 cranks that are drilled.... are drilled?
10-29-2003, 07:23 PM
#69
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Does any of this sound familiar ?
I think I have read that the GTS blocks are modifed in the crankcase with extra passages, anybody know for sure ?
-------------------------------------------------------------
Oiling System Snag
After the aluminum block and plastic intake, the most noticeable part on an LS1 is the oil pan. Sources involved in C5 testing call the intricate aluminum casting a "bat wing" pan. It's part of the lower engine structure and contributes to overall cylinder case rigidity. Gen III continues the recent tradition of little oil filters but the filter mounts on the rear of the oil pan rather than the block. As with LT1/4s, no oil cooler is available and the factory fill will be synthetic oil. Testing shows the oil temperature range to be similar to what we see in Gen II Small-Blocks.
The new engine uses a gerotor oil pump that is driven off the front of the crankshaft. Gerotor pumps are used in many recent engine designs. They are less complex, less costly to make and require less power to pump a given volume at a given pressure.
Oil distribution has changed significantly from that of the Small-Block because of: 1) the front pump, rear filter arrangement (the old engine had both at the back) and 2) the LS1's main oil galley feeding the main bearings and the camshaft simultaneously (the Small-Block main galley fed the cam bearings first, then the mains). John Juriga tells us that the Gen I/II oiling system was very reliable and that the change in oil routing in the new engine came mainly out of manufacturing concerns.
One of the unexpected challenges of the C5 vehicle development program centered around the LS1’s control of oil drainback and oil supply during high rpm operation with the vehicle sustaining maximum lateral acceleration (max. lat.), In February of '95, during maximum lateral acceleration testing on the skid pad at the GM Desert Proving Ground, problems with engine oiling began to crop up that were unrelated to earlier difficulty with cylinder case porosity. There may have been half-a-dozen or more engine failures due to this new problem. There was much head-scratching about why C5s were popping motors as if it were happy hour at a Winston Cup qualifying day.
By the end of the first quarter of 1995, it was established that the trouble was caused by two problems: 1) crankcase windage. The LS1's deep-skirted block, six-bolt main bearing caps and a higher oil level that goes with a shallower oil pan effectively divided the crankcase into four distinct "bays." Early blocks did not allow efficient transfer of air between bays as the pistons moved in their bores. At high rpm, the violent turbulence caused by this absence of pressure relief aerated the oil. This problem also restricted oil drain-back from the upper end of the engine. The combination of oil foaming and poor drainback degraded the oil supply. 2) lateral acceleration. At "max. lat.", oil level in the pan could reach a 45 degree angle from horizontal. Combine these two problems, sustain them for several seconds and, often, the oil pickup would suck air and oil pressure would be lost. No pressure meant certain engine bearing failure and that brought premature end to the testing excitement.
Throughout the summer and fall of 1995, the lights burned late in Powertrain Headquarters at GM's "Tech Center" in Warren Michigan. In the end, three solutions were found. First, to address the oil foaming and poor drain-back, the structure of the Gen III case was modified to allow pressure transfer between bays. Second, to improve oil supply at max. lat., a complex oil pan design incorporating sump extensions (the bat wings), extensive baffling and trap doors was devised. Third, to help with with the first two problems, the oil capacity was increased from four to six quarts.
Interestingly, the LS1 oil pan is reminiscent of the wet sump, road race oil pans used by amateur racers before SCCA allowed dry sump oiling systems in the mid-1970s. In fact, a dry sump oil system for LS1 was studied, but never went past the paper stage due to cost and concerns about low oil temperature during warm-up.
Last June, Project Manger Juriga assured us that the critical problem had been solved; however,we learned afterwards that the anomaly will still occur in extreme situations of high-rpm, sustained, max. lat. operation. An example might be abusive skid pad testing done by some of the less-experienced automotive media.
We also learned that, in an unusual solution, that in mid-’96 GM Powertrain wrote the LS1 PCM calibration such that, if high rpm and high lateral acceleration are sustained for a substantial length of time; the electronic throttle control (ECT) will reduce throttle opening to slow the car. In a follow-up interview in March of 1997 for the WWW versions of this story, John Juriga confirmed that the ’97 Vette’s PCM calibration is written that way.
We know C5 was tested extensively at the Road Atlanta, Road America and Grattan, Michigan road race tracks, so we believe that, in most real-world driving situations you’d see in a Corvette, including road racing; the LS1 oiling system is dead-nuts-reliable. However, if a LS1 is run on a skid pad at high-rpm and max. lat. for 45 or more seconds, we suspect that ECT will reduce the throttle opening.
---------------------------------------------------------------------------------------------------------------------------------
The LS6 and the LS1 use an all-aluminum cylinder case. It’s a "deep-skirted" design (block structure extends below the crankshaft centerline) with six-bolt main bearing caps (four vertical bolts and two horizontal bolts per cap) and head bolt threads deep in the main bearing bulkheads (for minimal block distortion and maximum head gasket clamping force). LS1/6 blocks are semi-permanent mold castings of 319-T5 aluminum. The LS6 case is different from LS1 blocks in the design and strength of the main bearing bulkheads.
As the pistons move up and down, they force air in and out of the spaces (or "bays") beneath them. At high rpm, this reciprocating air flow is violent and really whips up the oil. While the LS1 block has some machined openings between bays, the LS6 block, because the engine has about 500 more usable rpm, needed larger windows at the base of each cylinder to better accommodate "bay-to-bay breathing."
We got the GMPT guys to cut up a LS6 block for us. To above-left of the #2 main bearing bulkhead, at the bottom of the cylinder bore, you can easily see the rectangular bay-to-bay breathing window. Photo: author
Click Image For Larger View
Obviously, cutting windows at the bottom of each cylinder reduces the strength of the block’s key structural area, the main bearing bulkheads. With 40 more horsepower, 400-500 more rpm and even more powerful derivations of this engine to come, the block needed to be even stronger than it would be without the windows. It doesn’t take a rocket scientist to figure, in their ruthless pursuit of power, Dr. John and his engineers had to do more than simply reprogram their CNCs to cut those windows.
Finite element design work along with a lot of thrashing engines to death (in a few cases, literally) on the dyno eventually resulted in the special LS6 block having both the bay-to-bay breathing windows and more overall strength than the LS1 block
I think I have read that the GTS blocks are modifed in the crankcase with extra passages, anybody know for sure ?
-------------------------------------------------------------
Oiling System Snag
After the aluminum block and plastic intake, the most noticeable part on an LS1 is the oil pan. Sources involved in C5 testing call the intricate aluminum casting a "bat wing" pan. It's part of the lower engine structure and contributes to overall cylinder case rigidity. Gen III continues the recent tradition of little oil filters but the filter mounts on the rear of the oil pan rather than the block. As with LT1/4s, no oil cooler is available and the factory fill will be synthetic oil. Testing shows the oil temperature range to be similar to what we see in Gen II Small-Blocks.
The new engine uses a gerotor oil pump that is driven off the front of the crankshaft. Gerotor pumps are used in many recent engine designs. They are less complex, less costly to make and require less power to pump a given volume at a given pressure.
Oil distribution has changed significantly from that of the Small-Block because of: 1) the front pump, rear filter arrangement (the old engine had both at the back) and 2) the LS1's main oil galley feeding the main bearings and the camshaft simultaneously (the Small-Block main galley fed the cam bearings first, then the mains). John Juriga tells us that the Gen I/II oiling system was very reliable and that the change in oil routing in the new engine came mainly out of manufacturing concerns.
One of the unexpected challenges of the C5 vehicle development program centered around the LS1’s control of oil drainback and oil supply during high rpm operation with the vehicle sustaining maximum lateral acceleration (max. lat.), In February of '95, during maximum lateral acceleration testing on the skid pad at the GM Desert Proving Ground, problems with engine oiling began to crop up that were unrelated to earlier difficulty with cylinder case porosity. There may have been half-a-dozen or more engine failures due to this new problem. There was much head-scratching about why C5s were popping motors as if it were happy hour at a Winston Cup qualifying day.
By the end of the first quarter of 1995, it was established that the trouble was caused by two problems: 1) crankcase windage. The LS1's deep-skirted block, six-bolt main bearing caps and a higher oil level that goes with a shallower oil pan effectively divided the crankcase into four distinct "bays." Early blocks did not allow efficient transfer of air between bays as the pistons moved in their bores. At high rpm, the violent turbulence caused by this absence of pressure relief aerated the oil. This problem also restricted oil drain-back from the upper end of the engine. The combination of oil foaming and poor drainback degraded the oil supply. 2) lateral acceleration. At "max. lat.", oil level in the pan could reach a 45 degree angle from horizontal. Combine these two problems, sustain them for several seconds and, often, the oil pickup would suck air and oil pressure would be lost. No pressure meant certain engine bearing failure and that brought premature end to the testing excitement.
Throughout the summer and fall of 1995, the lights burned late in Powertrain Headquarters at GM's "Tech Center" in Warren Michigan. In the end, three solutions were found. First, to address the oil foaming and poor drain-back, the structure of the Gen III case was modified to allow pressure transfer between bays. Second, to improve oil supply at max. lat., a complex oil pan design incorporating sump extensions (the bat wings), extensive baffling and trap doors was devised. Third, to help with with the first two problems, the oil capacity was increased from four to six quarts.
Interestingly, the LS1 oil pan is reminiscent of the wet sump, road race oil pans used by amateur racers before SCCA allowed dry sump oiling systems in the mid-1970s. In fact, a dry sump oil system for LS1 was studied, but never went past the paper stage due to cost and concerns about low oil temperature during warm-up.
Last June, Project Manger Juriga assured us that the critical problem had been solved; however,we learned afterwards that the anomaly will still occur in extreme situations of high-rpm, sustained, max. lat. operation. An example might be abusive skid pad testing done by some of the less-experienced automotive media.
We also learned that, in an unusual solution, that in mid-’96 GM Powertrain wrote the LS1 PCM calibration such that, if high rpm and high lateral acceleration are sustained for a substantial length of time; the electronic throttle control (ECT) will reduce throttle opening to slow the car. In a follow-up interview in March of 1997 for the WWW versions of this story, John Juriga confirmed that the ’97 Vette’s PCM calibration is written that way.
We know C5 was tested extensively at the Road Atlanta, Road America and Grattan, Michigan road race tracks, so we believe that, in most real-world driving situations you’d see in a Corvette, including road racing; the LS1 oiling system is dead-nuts-reliable. However, if a LS1 is run on a skid pad at high-rpm and max. lat. for 45 or more seconds, we suspect that ECT will reduce the throttle opening.
---------------------------------------------------------------------------------------------------------------------------------
The LS6 and the LS1 use an all-aluminum cylinder case. It’s a "deep-skirted" design (block structure extends below the crankshaft centerline) with six-bolt main bearing caps (four vertical bolts and two horizontal bolts per cap) and head bolt threads deep in the main bearing bulkheads (for minimal block distortion and maximum head gasket clamping force). LS1/6 blocks are semi-permanent mold castings of 319-T5 aluminum. The LS6 case is different from LS1 blocks in the design and strength of the main bearing bulkheads.
As the pistons move up and down, they force air in and out of the spaces (or "bays") beneath them. At high rpm, this reciprocating air flow is violent and really whips up the oil. While the LS1 block has some machined openings between bays, the LS6 block, because the engine has about 500 more usable rpm, needed larger windows at the base of each cylinder to better accommodate "bay-to-bay breathing."
We got the GMPT guys to cut up a LS6 block for us. To above-left of the #2 main bearing bulkhead, at the bottom of the cylinder bore, you can easily see the rectangular bay-to-bay breathing window. Photo: author
Click Image For Larger View
Obviously, cutting windows at the bottom of each cylinder reduces the strength of the block’s key structural area, the main bearing bulkheads. With 40 more horsepower, 400-500 more rpm and even more powerful derivations of this engine to come, the block needed to be even stronger than it would be without the windows. It doesn’t take a rocket scientist to figure, in their ruthless pursuit of power, Dr. John and his engineers had to do more than simply reprogram their CNCs to cut those windows.
Finite element design work along with a lot of thrashing engines to death (in a few cases, literally) on the dyno eventually resulted in the special LS6 block having both the bay-to-bay breathing windows and more overall strength than the LS1 block
10-30-2003, 01:34 AM
#71
Burning Brakes
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Hi,
Lizard931 - The "use a synthetic" comment oil may confuse some people
The synthetic oil must have a high HT/HS viscosity( 4.1>cSt ), low NOAK volatility and a high flash point
In order to meet the above it will probably have a viscosity of from 15/20w low to 60 high ( eg 15w-50 )
Regards
Lizard931 - The "use a synthetic" comment oil may confuse some people
The synthetic oil must have a high HT/HS viscosity( 4.1>cSt ), low NOAK volatility and a high flash point
In order to meet the above it will probably have a viscosity of from 15/20w low to 60 high ( eg 15w-50 )
Regards
10-30-2003, 03:59 AM
#72
5th Gear
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Shouldn't we see a Low Oil Level indication at lh lateral accelerations. If oil pressure fluctuations are based on the lack of oil in the pan, wherever it comes from, then a warning should be created by the oil level warning indication.
Does anyone know the functional design of the S4 Low Oil Level indication system.
Is that function available only before engine start?
Is it while the engine runs?
Is it not reliable at rh lateral accelerations?
What is the tolerance between the indication and oil pressure fluctuations?
Bernd
Does anyone know the functional design of the S4 Low Oil Level indication system.
Is that function available only before engine start?
Is it while the engine runs?
Is it not reliable at rh lateral accelerations?
What is the tolerance between the indication and oil pressure fluctuations?
Bernd
10-30-2003, 04:57 AM
#74
Drifting
im confused as to whether the solution to the oiling problem is to have the crank drilled 'like a chevy' or not? in other words if you did this what rpm will the crank then sustain?
excellent pics martin!
excellent pics martin!
10-30-2003, 10:37 AM
#75
Nordschleife Master
I'd like to see a clear solution, too.
The confusing part, for me, is that the thread has covered four different problems related to oiling:
Oil ingestion at high RPM.
Oil pooling in heads at high RPM.
Oil sloshing away from pick-up in high g corners
Rod bearing failure.
Granted, there may be an interdependency, but the crank failures have occured for those that knew about that potential and didn't see oil pressure problems. Having more oil is better than less, for certain. If the oil volume is low (ingestion) and not in the pan (pooling) the pickup is more likely exposed (sloshing) and feeding foam or nothing to the bearings. Here's my take on the solutions:
Oil ingestion:
Use a better oil. Some have said Red Line was sucked out less.
Reduce piston ring blow-by. If it's wooshing through, there will be more removed.
Put in more scrapers. The GTS had extra ones.
Run the PCV line to a catch tank. Then it isn't sucked out and won't create smoke in any case.
Lower shift points.
Oil Pooling: Haven't followed this. Anyone?
Oil sloshing:
Add more baffles in the pan. Maybe the extra GT baffle plate.
Keep oil level up.
Be aware what the limits of your car is.
Crank Failure:
Drill "like a Chevy." (Can someone explain this better? )
Add an Accusump.
Add dry sump
Use better oil like Amsoil or Red Line.
In the absence of dry sump and maybe Accusump, lower shift points.
Anyone have any additions/corrections?
The confusing part, for me, is that the thread has covered four different problems related to oiling:
Oil ingestion at high RPM.
Oil pooling in heads at high RPM.
Oil sloshing away from pick-up in high g corners
Rod bearing failure.
Granted, there may be an interdependency, but the crank failures have occured for those that knew about that potential and didn't see oil pressure problems. Having more oil is better than less, for certain. If the oil volume is low (ingestion) and not in the pan (pooling) the pickup is more likely exposed (sloshing) and feeding foam or nothing to the bearings. Here's my take on the solutions:
Oil ingestion:
Use a better oil. Some have said Red Line was sucked out less.
Reduce piston ring blow-by. If it's wooshing through, there will be more removed.
Put in more scrapers. The GTS had extra ones.
Run the PCV line to a catch tank. Then it isn't sucked out and won't create smoke in any case.
Lower shift points.
Oil Pooling: Haven't followed this. Anyone?
Oil sloshing:
Add more baffles in the pan. Maybe the extra GT baffle plate.
Keep oil level up.
Be aware what the limits of your car is.
Crank Failure:
Drill "like a Chevy." (Can someone explain this better? )
Add an Accusump.
Add dry sump
Use better oil like Amsoil or Red Line.
In the absence of dry sump and maybe Accusump, lower shift points.
Anyone have any additions/corrections?