Louis Ott's full valve cover video now on youtube
05-23-2010, 01:08 AM
#16
Race Director
When you get up past 30% there is great risk to the rod bearings; past 50% to the mains. Remember that in a dynamic circuit the pressure will drop as you get farther into the system. Cosworth developed a method to measure the aeration in realtime on an engine by using this differential. It is highly sensitive to sensor location and would need to be calibrated engine to engine as well. If the oil is supersaturated the gases will start evolving out with pressure drops and cause all sorts of problems.
I have seen over 140psi cold.....and still well over 5bar (73.5psi) at 5000rpm...even at HOT oil temps....even after HOURS racing with no oil cooler the Lemons racer would still show 100+psi at say 5000rpm....
475hp/460lb.ft
05-23-2010, 04:24 PM
#18
Nordschleife Master
Thread Starter
The oil pump is positive displacement and has a lot of capacity. At higher rpm, I believe the pump relief spring is controlling the oil pressure. If true, the oil flow at the pump outlet doesn't change the oil pressure. It just changes the fraction of time that the relief valve is open. Changing a lower load spring to the relief valve I believe would lower the oil pressure.
Last edited by ptuomov; 05-23-2010 at 11:04 PM.
05-23-2010, 04:27 PM
#19
Nordschleife Master
As I understand it the pump is a constant volume per revolution type, so while a lower viscosity oil would show lower pressure, like many owners experience with the latest version of Mobil One, the volume of oil pumped would not change and when the level in the sump dropped sufficiently the pump would suck air as it does now.
Lower foam oil might help, maybe less detergent, but I think oil type is more a bandaid that might help, but not solve the problem.
Lower foam oil might help, maybe less detergent, but I think oil type is more a bandaid that might help, but not solve the problem.
05-23-2010, 05:00 PM
#20
Burning Brakes
With regard to the 2/6 bearing issue . I was talking to Mike Simard about oiling issues , He said that the channel that feeds the 2/6 bearings might be suffering from a venturi effect as the volume in the main oil channel increases with rpm ? Just like you used to drain a water bed using a water tap and a T conector to suck the water out . ??
05-23-2010, 05:24 PM
#21
Nordschleife Master
Thread Starter
As I understand it the pump is a constant volume per revolution type, so while a lower viscosity oil would show lower pressure, like many owners experience with the latest version of Mobil One, the volume of oil pumped would not change and when the level in the sump dropped sufficiently the pump would suck air as it does now.
A link to attachment of one of Louis Ott's posts on the topic:
05-23-2010, 05:27 PM
#22
Nordschleife Master
Thread Starter
With regard to the 2/6 bearing issue . I was talking to Mike Simard about oiling issues , He said that the channel that feeds the 2/6 bearings might be suffering from a venturi effect as the volume in the main oil channel increases with rpm ? Just like you used to drain a water bed using a water tap and a T conector to suck the water out . ??
05-23-2010, 05:31 PM
#23
Racer
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As I understand it the pump is a constant volume per revolution type, so while a lower viscosity oil would show lower pressure, like many owners experience with the latest version of Mobil One, the volume of oil pumped would not change and when the level in the sump dropped sufficiently the pump would suck air as it does now.
Lower foam oil might help, maybe less detergent, but I think oil type is more a bandaid that might help, but not solve the problem.
Lower foam oil might help, maybe less detergent, but I think oil type is more a bandaid that might help, but not solve the problem.
05-23-2010, 05:55 PM
#24
Race Director
With regard to the 2/6 bearing issue . I was talking to Mike Simard about oiling issues , He said that the channel that feeds the 2/6 bearings might be suffering from a venturi effect as the volume in the main oil channel increases with rpm ? Just like you used to drain a water bed using a water tap and a T conector to suck the water out . ??
Heres an interesting article....
http://www.carcraft.com/techarticles...mps/index.html
It should be noted they are quoted a lowly 6gpm and 50-68psi..... At those oil temps the 928 would be WAY over that...the highest flow they got was 7.4gpm using really light oil....our 928's flow that much near 1700rpm....
05-23-2010, 06:01 PM
#25
Nordschleife Master
05-23-2010, 06:18 PM
#26
Race Director
05-24-2010, 12:50 AM
#27
Nordschleife Master
Sounds like a huge overkill and a big waste of power.
Mulling it over it does feel about right. The oil pump is really big and the sprockets aren't stepping down the RPMs a lot. Maybe 3:1 or 4:1. Picture the little oil pumps on a US V8 with the pump driven off the distributor rod (2:1). Much less volume in the pump gears. That's what they think is enough.
What'd be good is if the oil was all fed through the cooler before being returned to the pan, but it isn't.
Mulling it over it does feel about right. The oil pump is really big and the sprockets aren't stepping down the RPMs a lot. Maybe 3:1 or 4:1. Picture the little oil pumps on a US V8 with the pump driven off the distributor rod (2:1). Much less volume in the pump gears. That's what they think is enough.
What'd be good is if the oil was all fed through the cooler before being returned to the pan, but it isn't.
05-24-2010, 01:09 AM
#28
Rennlist Member
05-24-2010, 04:09 AM
#30
Anyone around here use a vacuum pump on the crankcase or a breather kit tied to the exhaust to pull a vacuum? You know, it could be a small part of the benefit to a dry sump. Many of their scavenge pumps use a lobed positive displacement "blower" on the scavenge stages so they pull a bit of air out as well. It seems simple to conclude if windage is a significant part of the equation to remove a good portion of the air.