scoping out interest for new 3.0 cranks.
02-11-2005, 01:50 AM
#32
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Any automotive manufacturing company with some engineering competency (and I certainly count Porsche as such) have simulation tools, which calculate polar pressure diagrams of a journal bearing. The oil hole is then located at the angle, where the low pressure occurs, so oil is sucked in to the bearing rather than pushed out.
We have had this discussion before and Bengt is right, that cross or perpendicular drilling has not been proven to solve the occasional #2 bearing oil starvation problem. Good oil pan baffling and/or slight overfilling, when the engine is going to be pushed hard, seem to be successful.
I also think it makes sense to keep adequate mass on the counterweights to ensure minimum bending of the crankshaft due to inertia forces. The throttle response effect of the added rotational inertia is being drowned by turbo response time.
Laust
We have had this discussion before and Bengt is right, that cross or perpendicular drilling has not been proven to solve the occasional #2 bearing oil starvation problem. Good oil pan baffling and/or slight overfilling, when the engine is going to be pushed hard, seem to be successful.
I also think it makes sense to keep adequate mass on the counterweights to ensure minimum bending of the crankshaft due to inertia forces. The throttle response effect of the added rotational inertia is being drowned by turbo response time.
Laust
02-11-2005, 03:45 PM
#34
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Originally Posted by Tom M'Guinn
You know, if you could squeeze a 94mm throw into a 3 liter block, you'd have a 3.2 liter with stock bores....
02-11-2005, 09:48 PM
#35
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From an "interested" standpoint you can toss my name in as well. Code Red is about due for some major performance modifications - might as well go whole hog. I've been thinking quite a lot about taking her off the street and heading for the track. Time frame would be later this year for me as well.
02-11-2005, 09:54 PM
#36
"The oil holes are in the correct place where oil can feed just before it is needed. All cranks have the holes this way"
No they don't. Take a look at a Crank made for racing where the Oil supply at higher RPMs is required. You won't see many drilled the same as the stock 944 Crank is. They are usually drilled thro the Rod journal straight into the Main, with no change of direction with big chamfered reliefs at the Journals.
Regardless of where and how the Oil should be feed to the Rod journals, the issue here is the #2 Rod bearing, and the problem is not how the oil flows thro the Crank. Any drilling different to stock will make absolutely no difference. The problem is in the Oil pan.
No they don't. Take a look at a Crank made for racing where the Oil supply at higher RPMs is required. You won't see many drilled the same as the stock 944 Crank is. They are usually drilled thro the Rod journal straight into the Main, with no change of direction with big chamfered reliefs at the Journals.
Regardless of where and how the Oil should be feed to the Rod journals, the issue here is the #2 Rod bearing, and the problem is not how the oil flows thro the Crank. Any drilling different to stock will make absolutely no difference. The problem is in the Oil pan.
02-11-2005, 10:56 PM
#38
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"We have had this discussion before and Bengt is right, that cross or perpendicular drilling has not been proven to solve the occasional #2 bearing oil starvation problem. Good oil pan baffling and/or slight overfilling, when the engine is going to be pushed hard, seem to be successful.
I also think it makes sense to keep adequate mass on the counterweights to ensure minimum bending of the crankshaft due to inertia forces. The throttle response effect of the added rotational inertia is being drowned by turbo response time."
Now Laust, I'm just trying to interpret what you're saying here, so correct my understanding if I'm wrong, but You think cross drilling, or perp frilling, and knife edging the crank, is jsut a waste of money, because you don't think that there is any real evidence that it makes any difference. In fact you think it may only unnecessarily weaken the crank. Is that right? TIA
I also think it makes sense to keep adequate mass on the counterweights to ensure minimum bending of the crankshaft due to inertia forces. The throttle response effect of the added rotational inertia is being drowned by turbo response time."
Now Laust, I'm just trying to interpret what you're saying here, so correct my understanding if I'm wrong, but You think cross drilling, or perp frilling, and knife edging the crank, is jsut a waste of money, because you don't think that there is any real evidence that it makes any difference. In fact you think it may only unnecessarily weaken the crank. Is that right? TIA
02-11-2005, 10:58 PM
#39
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I'm a big fan of cross drilling and perp drilling, but as I stated much earlier, both would be unnecessary if the hole was simply drilled in the correct spot to begin with.
A good point was brought up, how much longer could you make the throw?... maybe another couple mm?
A good point was brought up, how much longer could you make the throw?... maybe another couple mm?
02-11-2005, 11:47 PM
#40
"I'm a big fan of cross drilling and perp drilling, but as I stated much earlier, both would be unnecessary if the hole was simply drilled in the correct spot to begin with."
Correct!
Knife Edging the Counterweights and Counterweight mass are 2 different subjects. Knife Edging should not weaken the Crank unless done to excess at the Rod Pin. The counterweight mass of a 944 Crank based upon the Stock Pistons, Rods, Pins etc is 39% of the total reciprocating mass. This is high for performance engines, but typical for street engines where low engine vibration and balance is wanted. Most race Cranks have a lot less, and in some case have none. Torsional Dampners are used where high torsional forces are present, usually in the 2nd and 3rd orders.
Today it is typical that the counterweights are very round and have a lot of shape to them. In road racing, carrying a little higher conterweight often is liked over low mass. The engine tends to slow down slowerunder braking, and the driver can carry higher revs thro the corner and the acceleration out is better due to the higher revs. I remember the 2.0L BMW Touring car engines. Very low mass, and you could not brake heavy as the engine would almost stop, then absolutely no torqure to pull you out of the corner. High revs thro the corner and sideways, steering on the throttle.
Correct!
Knife Edging the Counterweights and Counterweight mass are 2 different subjects. Knife Edging should not weaken the Crank unless done to excess at the Rod Pin. The counterweight mass of a 944 Crank based upon the Stock Pistons, Rods, Pins etc is 39% of the total reciprocating mass. This is high for performance engines, but typical for street engines where low engine vibration and balance is wanted. Most race Cranks have a lot less, and in some case have none. Torsional Dampners are used where high torsional forces are present, usually in the 2nd and 3rd orders.
Today it is typical that the counterweights are very round and have a lot of shape to them. In road racing, carrying a little higher conterweight often is liked over low mass. The engine tends to slow down slowerunder braking, and the driver can carry higher revs thro the corner and the acceleration out is better due to the higher revs. I remember the 2.0L BMW Touring car engines. Very low mass, and you could not brake heavy as the engine would almost stop, then absolutely no torqure to pull you out of the corner. High revs thro the corner and sideways, steering on the throttle.
02-12-2005, 08:39 AM
#41
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You don't want to put the oil hole in a high pressure area like with perp drilling or cross drilling because that way you actually reduce bearing area. By having the hole 90 degrees before the high pressure area starts, you make sure that there is oil in the right spot when needed. Have a look at a Chevy crank and you will see that the placement is the same. It is correct though that in a chevy crank the hole is drilled straight but there is no difference caused by that the oil has to make 90 degree turn.
One of the weaknesses with the Porsche crank is the large diameter main journal. This cause high centrifugal forces working against the oil pressure. Since the oil therefore may be striving in different directions the oil can "break" with a gas bubble formed in the crank. This is especially likely if there is gas dissolved in the oil from windage.
Bengt
One of the weaknesses with the Porsche crank is the large diameter main journal. This cause high centrifugal forces working against the oil pressure. Since the oil therefore may be striving in different directions the oil can "break" with a gas bubble formed in the crank. This is especially likely if there is gas dissolved in the oil from windage.
Bengt
02-12-2005, 08:47 PM
#42
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The auction starts at Southeby's, on June 14 at an opening bid of 1.2 ,illoin dollars. Whose in?
The auction starts at Southeby's, on June 14 at an opening bid of 1.2 ,illoin dollars. Whose in?
02-13-2005, 12:37 PM
#44
"You don't want to put the oil hole in a high pressure area like with perp drilling or cross drilling because that way you actually reduce bearing area. By having the hole 90 degrees before the high pressure area starts, you make sure that there is oil in the right spot when needed. Have a look at a Chevy crank and you will see that the placement is the same. It is correct though that in a chevy crank the hole is drilled straight but there is no difference caused by that the oil has to make 90 degree turn.
One of the weaknesses with the Porsche crank is the large diameter main journal. This cause high centrifugal forces working against the oil pressure. Since the oil therefore may be striving in different directions the oil can "break" with a gas bubble formed in the crank. This is especially likely if there is gas dissolved in the oil from windage."
Cannot disagree more.
Some questions and answers to help make my point.
1. When measuring the clearanvce between the Rod bearing and Crank Journal, which direction is the Rod bearing measured? Only in the vertical.
2. Where is the thickess part of the Rod bearing? Or where is the thinnest part? Thickess part is 90 degrees to the parting Line. The thinnest part is at the parting line.
3. At what point of the Bearing or Crank Journal is the heaviest load applied under Compression? At 90 degrees to the parting line.
4. Where would you want the Oil supplied to give the best control? At the heaviest loaded part.
5. What keeps the bearing off the crank at all times? OIL and oil Pressure.
If you give these questions some thought you will see that the Oil is required at the heaviest loaded part of the Journal, and does not want to be turned when pumped up from the Main. I think we may be talking about the same here, but I'm not sure.
The oil hole wants to be a straight shot from the Main to the Rod journal without any turns. Under RPM or centrifigal forces, Oil does not want to turn, and its pressure from the Pump that makes it get to the Journal. Thats why the Rod Bearings will always fail first as they are the last to see the oil and the pressure is lower the further the oil is pumped. On cranks where larger clearances are required the oil galleys are restricted in other parts of the engine to help provide more pressure at the crank. Sometimes the volume is increased at the Crank as well. One of the most common restrictions is placed at the Cylinder Head IN port, as most Head are supplied way too much oil.
The size of the 944 Main is smaller than some Big Blocks and many other Cranks. This has nothing to do with how the oil is under any outside forces.
When the 2nd Rod bearing fails, a lot of people thought is was due to Oil starvation. It is. But they also thought that if you drilled the Journal across or perpendicular, you would provide more oil to the bearing and the problem was solved. Wrong. If no oil can be supplied to the Crank, then whatever number of holes or even where they are placed will make no difference. The problem is in the Oil Pan. The 944 Cranks are drilled as they are from the factory. They work when the oil is feed to the Crank. If you were to build a crank from scratch, then one would want to place ther holes in the correct place in the first place.
One of the weaknesses with the Porsche crank is the large diameter main journal. This cause high centrifugal forces working against the oil pressure. Since the oil therefore may be striving in different directions the oil can "break" with a gas bubble formed in the crank. This is especially likely if there is gas dissolved in the oil from windage."
Cannot disagree more.
Some questions and answers to help make my point.
1. When measuring the clearanvce between the Rod bearing and Crank Journal, which direction is the Rod bearing measured? Only in the vertical.
2. Where is the thickess part of the Rod bearing? Or where is the thinnest part? Thickess part is 90 degrees to the parting Line. The thinnest part is at the parting line.
3. At what point of the Bearing or Crank Journal is the heaviest load applied under Compression? At 90 degrees to the parting line.
4. Where would you want the Oil supplied to give the best control? At the heaviest loaded part.
5. What keeps the bearing off the crank at all times? OIL and oil Pressure.
If you give these questions some thought you will see that the Oil is required at the heaviest loaded part of the Journal, and does not want to be turned when pumped up from the Main. I think we may be talking about the same here, but I'm not sure.
The oil hole wants to be a straight shot from the Main to the Rod journal without any turns. Under RPM or centrifigal forces, Oil does not want to turn, and its pressure from the Pump that makes it get to the Journal. Thats why the Rod Bearings will always fail first as they are the last to see the oil and the pressure is lower the further the oil is pumped. On cranks where larger clearances are required the oil galleys are restricted in other parts of the engine to help provide more pressure at the crank. Sometimes the volume is increased at the Crank as well. One of the most common restrictions is placed at the Cylinder Head IN port, as most Head are supplied way too much oil.
The size of the 944 Main is smaller than some Big Blocks and many other Cranks. This has nothing to do with how the oil is under any outside forces.
When the 2nd Rod bearing fails, a lot of people thought is was due to Oil starvation. It is. But they also thought that if you drilled the Journal across or perpendicular, you would provide more oil to the bearing and the problem was solved. Wrong. If no oil can be supplied to the Crank, then whatever number of holes or even where they are placed will make no difference. The problem is in the Oil Pan. The 944 Cranks are drilled as they are from the factory. They work when the oil is feed to the Crank. If you were to build a crank from scratch, then one would want to place ther holes in the correct place in the first place.
02-13-2005, 02:04 PM
#45
To edit my last post, I just made a call and asked about the hole placement. Its always just of center, but still a direct shot from the main. So the hole is angled ever so slightly of the Rod journal cenerline, but still not a 90 degrees.