Girdle oil passage modifications
10-03-2009, 02:57 PM
#46
Nordschleife Master
This gets to the question of how fast the oil is moving and what the pressure drop is along the other passages.
10-03-2009, 03:05 PM
#47
Nordschleife Master
Thread Starter
Yes. But here's the one thing I don't get. Why didn't the Porsche engineers reduce the manifold passage diameter after the #2 main entrance? They did it in every single other point when oil flow is taken from the distributing channel. That's why they have those steps. But why on earth they didn't do it at the #2 main?
10-03-2009, 04:32 PM
#48
Nordschleife Master
I'd be careful about removing material from the inner wall. Blending the floor looks attractive. The "middle" wall could take some tapering, too.
10-03-2009, 05:10 PM
#49
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Ok I'm going to start beating on my drum now. If issues with sealing, thinning walls on the girdle, etc. make one nervous my idea of drilling the main down through the top is super simple. I mean, it removes lots of gray area and would be cheap to make. I wish I had more $ for some basic R&D because I have the means to do it all. Other than clearing a stock intake I can't see the down side. The engine has to be disassembled to modify the girdle anyway, why not the block?
10-03-2009, 08:18 PM
#50
Nordschleife Master
Thread Starter
That could work, but I am trying to do the bare minimum tweaking necessary.
Ok I'm going to start beating on my drum now. If issues with sealing, thinning walls on the girdle, etc. make one nervous my idea of drilling the main down through the top is super simple. I mean, it removes lots of gray area and would be cheap to make. I wish I had more $ for some basic R&D because I have the means to do it all. Other than clearing a stock intake I can't see the down side. The engine has to be disassembled to modify the girdle anyway, why not the block?
10-03-2009, 08:31 PM
#51
Nordschleife Master
A demonstrated solution, or at lest a big improvement, is modifying the crank. Not cheap but nothing will be. Thinking about it, is the improvement with the drilling that the bearing is fed from a second main (#3) that has better oil pressure?
10-03-2009, 08:31 PM
#52
Race Director
granted I'm not an engineer...but one thing I DO NOT understand is why Porsche removed the GREAT oil pan system they used in early cars....and went too the flawed design used in S4+.....the early system has a mesh baffle with plastic center cup and an exact center position oil feed tube that seals the plastic cup with O rings.....the S4+ is offset of the left (why it starves more on left turns) with NO baffling at all..it had to be a cost item since Porsche did not race the car and figured no customers would either...but when they designed the car as a 911 replacement...clearly they thought about racing it, which is why the better pan was in the early cars...
10-03-2009, 08:32 PM
#53
Race Director
Where does the pressurized oil come from? Could you diagram this for us?
A demonstrated solution, or at lest a big improvement, is modifying the crank. Not cheap but nothing will be. Thinking about it, is the improvement with the drilling that the bearing is fed from a second main (#3) that has better oil pressure?
A demonstrated solution, or at lest a big improvement, is modifying the crank. Not cheap but nothing will be. Thinking about it, is the improvement with the drilling that the bearing is fed from a second main (#3) that has better oil pressure?
10-03-2009, 08:46 PM
#54
Nordschleife Master
Thread Starter
http://gallery.lasttenth.com/main.php?g2_itemId=1440
The path descriptions by Dennis Kao:
For a stock 928 crankshaft the:
1-5 rod journal is connected to the #1 main cross-drill
2-6 rod journal is connected to the #2 main cross-drill
3-7 rod journal is connected to the #4 main cross-drill
4-8 rod journal is connected to the #5 main cross-drill
The #3 main (center thrust bearing journal) has no cross -drill
Taylor-drilling leaves all of these existing oil passages in place but then adds a bunch more. They add:
new cross-drills at #2, #3 and #4 mains
connect 1-5 rod journal to #2 main
connect 2-6 & 3-7 rod journals to #3 main
connect 4-8 rod journal to #4 main
With a stock 928 crank, each rod journal is supplied from a single main. After modification, each rod journal is supplied from two adjacent mains. For example, in the stock crank the 4-8 rod journal is supplied from the #5 main. Taylor adds a cross-drill at the #4 main. They drill out the existing plug and extend the intercept from the #4 rod cross-drill to the #4 main. The whole oiling system within the crank is now inter-linked.
10-03-2009, 09:02 PM
#55
Race Director
Tuomo
That makes ALOT of sense..... so all rod bearings are fed from two mains vs just 1 before....that has to be good.....
However even after all the improvements I made to my oiling system...I was still seeing 3ish bar in turns...oddly enough most of them were right turns...the pressure didn't drop as much in left turns? Odd...very odd...
However after 4 run sessions totalling almost 1.5 hours on track....the oil was spotlessly clean...I've never seen oil that clean after hard running
That makes ALOT of sense..... so all rod bearings are fed from two mains vs just 1 before....that has to be good.....
However even after all the improvements I made to my oiling system...I was still seeing 3ish bar in turns...oddly enough most of them were right turns...the pressure didn't drop as much in left turns? Odd...very odd...
However after 4 run sessions totalling almost 1.5 hours on track....the oil was spotlessly clean...I've never seen oil that clean after hard running
10-11-2009, 06:48 PM
#56
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I disagree with one thing, though. If the oil distributing manifold channel has constant cross-sectional area, the exit closest to the pump will see the lowest static pressure.
Suppose that you take a garden hose and plug it in one end and feed water at pressure from the other end. Then, drill same size holes in the garden hose. When you turn the water pressure on, water will first come in from the hole closest to the plugged end and last from the hole closest to the flow source. Furthermore, the far away hole will squirt the oil at high pressure and the near hole will have water barely trickling out. This is because the flow speed is highest in the hose at the near hole and slowest at the far away hole.
The way to remedy this is to reduce the hose size after every hole in away that the flow speed remains constant. This way, the water will flow out at same pressure from all holes.
Perhaps I misundersood what you meant, in that case sorry about my naive lecturing.
The situation in the 928 girdle is exactly analogous. It is inexplicable to me why the cross-sectional area is not larger before the #2 main than after. The flow needs to be slowed down at the #2 main entrance! It looks very much like design error to me, which is very surprising given that those Porsche engineers obviously understand this.
Suppose that you take a garden hose and plug it in one end and feed water at pressure from the other end. Then, drill same size holes in the garden hose. When you turn the water pressure on, water will first come in from the hole closest to the plugged end and last from the hole closest to the flow source. Furthermore, the far away hole will squirt the oil at high pressure and the near hole will have water barely trickling out. This is because the flow speed is highest in the hose at the near hole and slowest at the far away hole.
The way to remedy this is to reduce the hose size after every hole in away that the flow speed remains constant. This way, the water will flow out at same pressure from all holes.
Perhaps I misundersood what you meant, in that case sorry about my naive lecturing.
The situation in the 928 girdle is exactly analogous. It is inexplicable to me why the cross-sectional area is not larger before the #2 main than after. The flow needs to be slowed down at the #2 main entrance! It looks very much like design error to me, which is very surprising given that those Porsche engineers obviously understand this.
There is a good article in the 1910 Encyclopedia Britannica under the heading Hydraulics that discusses this idea with respect to hoses and municipal water systems. Very well written and illustrated presentation.
10-11-2009, 07:44 PM
#57
Nordschleife Master
Thread Starter
I think Greg mentioned the hose filling analogy a few years ago. That is an initial condition of the system in the first few seconds or less. Once the system stabilizes it is different. Pressure in a hose drops in relation to length in a dynamic system.
There is a good article in the 1910 Encyclopedia Britannica under the heading Hydraulics that discusses this idea with respect to hoses and municipal water systems. Very well written and illustrated presentation.
There is a good article in the 1910 Encyclopedia Britannica under the heading Hydraulics that discusses this idea with respect to hoses and municipal water systems. Very well written and illustrated presentation.
Moving to the garden hose example. There are two effects here, I think. The first is that there is a pressure loss due to friction in a pipe when the fluid is flowing. A garden hose even without holes in it is going to lose some pressure if it's long and if the fluid is flowing. Faster it flows, larger the potential for pressure loss.
The second is that even in the absence of frictions, the static pressure is lower if the fluid flows faster. When you play with a plugged constant-diameter garden hose that has holes drilled in it, this latter effect is the dominant one.
10-11-2009, 10:49 PM
#58
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No, some oils may have negligible amounts of air dissolved in them but paraffinic oils typically have 9% air at operating temperatures and ambient pressure. The same holds true for gasoline and diesel fuel.
10-11-2009, 11:14 PM
#59
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Moving to the garden hose example. There are two effects here, I think. The first is that there is a pressure loss due to friction in a pipe when the fluid is flowing. A garden hose even without holes in it is going to lose some pressure if it's long and if the fluid is flowing. Faster it flows, larger the potential for pressure loss.
The second is that even in the absence of frictions, the static pressure is lower if the fluid flows faster. When you play with a plugged constant-diameter garden hose that has holes drilled in it, this latter effect is the dominant one.
The second is that even in the absence of frictions, the static pressure is lower if the fluid flows faster. When you play with a plugged constant-diameter garden hose that has holes drilled in it, this latter effect is the dominant one.
The soaker hose analogy would be interesting if the catastrophic damage to the 2/6 bearings occured in the first few seconds of operation prior to an equilibrium in the system being reached -- this does not appear to be the case.