Louis Ott's full valve cover video now on youtube
05-21-2010, 06:26 PM
#1
Nordschleife Master
Thread Starter
Louis Ott's full valve cover video now on youtube
Kevin Johnson has posted Louis Ott's valve cover video on youtube.com:
To see how the problems show up in left-hand corners, here's the track on which the video was shot:
Big left hander, big problems. Small left hander, small problems.
Here's the whole story from Ott's Performance Engineering web page:
http://www.performance928.com/cgi-bi...ss_parent=1128
After I burned my 2/6 rod bearings, I decided to investigate the crankcase oil control and breather system further to determine if this contributed to the oil starvation problem. I obtained a cam cover from Marc Thomas. I cut several holes in it and installed lexan windows. With a small video camera and light, I could see and record, what was happening to oil inside the cam cover while the engine was running.
These are pictures while the engine is running. The picture on the left is at high rpm while the car is moving in a straight line. The picture on the right is during a high speed, high rpm left turn. The engine is fitted with a GTS sump baffle and Accusump. The oil is Redline 20W 50.
In the left side picture, you can see the cam shaft bearing cap and the cam lobe is turning on the left side of the bearing cap. There is quite a lot of oil, but not so much that oil is trapped in the cam cover. It was freely running down the drain back holes with no "pooling" of excess oil. There is a thought that one of the reasons for oil starvation is that at high rpm too much oil is pumped into the upper cylinder head area which deprives the oil sump of sufficient oil. This is incorrect.
The right side picture shows what happens immediately after entering a left sweeping turn at high speed and high RPM. The oil turns to froth and there appeared to be a lot more of it although it was difficult to tell. The frothy oil was likely not coming directly through the pressure fed oiling system. It was probably being whipped by the crankshaft and was being blown upward through the oil drain back holes from the oil sump area.
I reached this conclusion after seeing it happen and doing research on how crankcase breather systems are designed for high performance engines. I found that the 928 has extremely limited crankcase breathing capacity. The 928 (32 valve motors) have two 12mm exits from the oil filler base into the breather system. One of those 12mm hoses is further restricted by a valve with a small opening. The recommended crankcase breather size for a 5.0 liter engine is an opening of 3/4" diameter or larger.
With insufficient breathing capacity to relieve crankcase pressure, the only route for the blow by gasses is up through the drain back holes in the cylinder head, out the breather connections in the cam cover, and eventually into the intake system. The crankshaft rotation throws oil to the right side (viewed from the rear) of the engine crankcase which causes oil to be blown up the drainback holes into the right side cam cover. The right side cam cover has the only breather connections on S4 & GT engines. This undoubtedly exacerbates the propensity for these engines to blow oil into the intake system when being run hard. The GTS engines have cam cover breather connections on both sides which may help. A sustained left turn is even worse with oil in the sump being forced to the right side.
We can make some changes to give better oil control with less oil lost to the intake, and provide better lubrication for the engine. I'll give examples of what I did, or plan to do. Other approaches may work as well, or better. Improvements should address three areas.
1. Both cam covers should have breathers.
2. Increase crankcase breathing capacity.
3. Provide effective oil control in the sump.
My plan was to supply fresh air to the cam cover breathers, install a larger crankcase breather outlet, and vent the blow by gasses into a vacuum source in the exhaust. I didn't use any of the stock breather system other than the cam cover breather fittings. The two 12mm outlets in the base of the oil filler were plugged.
1. Both cam covers should have breathers. A breather fitting was installed on the left cam cover in the rear hole. An oil control shroud was used under the fitting (inside the cam cover) the same as on the right rear breather fitting. The small passageway in the right rear breather fitting was drilled out to the same size as the front fitting. The front right cam cover breather was removed and the hole plugged using the plug from the left rear cam cover hole. The breathers were supplied with fresh filtered air from the air box below the air filter. This was accomplished by drilling holes in the air box and using a rubber hose to connect the breather fittings to the air box holes. Rubber grommets in the holes with the ID sized for a tight fit to the rubber hose insures a secure and dust free seal between the air box and hose. Now, the cam covers will receive clean air which will flow into the cam covers and down the oil drain back holes to the crankcase. This air will flush combustion byproducts out of the engine.
2. Increase crankcase breathing capacity. A vented oil filler cap was made using the stock cap as the interior to retain the threads and seal. An aluminum cover was constructed with a swiveling center to permit the cap to rotate around the vent line. The center part is made from brass and retained in the cover by an "O" ring. Illustrations are shown below.
Oil filler cap breather
Oil filler cap breather underside
3. Provide effective oil control in the sump. Nearly all the high performance engine building books I use recommend use of crankshaft oil scrapers, a windage tray, and a surge baffle in the oil sump. The books that don't recommend the surge baffle recommend instead that a dry sump oil system be used. I chose to stay with the 928 wet sump oil system to reduce cost, weight, and overall complexity. The design of the 928 oil sump is in some ways good, and some not so good. It's good in that the sump does have internal baffles and a flange of sorts around the sump edges to reduce the oil climbing the sides during high "G" cornering. Also, the oil pickup is in the center of the sump with a generous sized pickup tube and well designed inlet. It's not so good because it is much too shallow with insufficient distance between the crank counterweights and the oil. The pan floor is so close to the crank that a windage tray, or screen, can't easily be fitted.
Copyright 2004-2010, OTT'S PERFORMANCE ENGINEERING. All Rights Reserved.
To see how the problems show up in left-hand corners, here's the track on which the video was shot:
Big left hander, big problems. Small left hander, small problems.
Here's the whole story from Ott's Performance Engineering web page:
http://www.performance928.com/cgi-bi...ss_parent=1128
After I burned my 2/6 rod bearings, I decided to investigate the crankcase oil control and breather system further to determine if this contributed to the oil starvation problem. I obtained a cam cover from Marc Thomas. I cut several holes in it and installed lexan windows. With a small video camera and light, I could see and record, what was happening to oil inside the cam cover while the engine was running.
These are pictures while the engine is running. The picture on the left is at high rpm while the car is moving in a straight line. The picture on the right is during a high speed, high rpm left turn. The engine is fitted with a GTS sump baffle and Accusump. The oil is Redline 20W 50.
In the left side picture, you can see the cam shaft bearing cap and the cam lobe is turning on the left side of the bearing cap. There is quite a lot of oil, but not so much that oil is trapped in the cam cover. It was freely running down the drain back holes with no "pooling" of excess oil. There is a thought that one of the reasons for oil starvation is that at high rpm too much oil is pumped into the upper cylinder head area which deprives the oil sump of sufficient oil. This is incorrect.
The right side picture shows what happens immediately after entering a left sweeping turn at high speed and high RPM. The oil turns to froth and there appeared to be a lot more of it although it was difficult to tell. The frothy oil was likely not coming directly through the pressure fed oiling system. It was probably being whipped by the crankshaft and was being blown upward through the oil drain back holes from the oil sump area.
I reached this conclusion after seeing it happen and doing research on how crankcase breather systems are designed for high performance engines. I found that the 928 has extremely limited crankcase breathing capacity. The 928 (32 valve motors) have two 12mm exits from the oil filler base into the breather system. One of those 12mm hoses is further restricted by a valve with a small opening. The recommended crankcase breather size for a 5.0 liter engine is an opening of 3/4" diameter or larger.
With insufficient breathing capacity to relieve crankcase pressure, the only route for the blow by gasses is up through the drain back holes in the cylinder head, out the breather connections in the cam cover, and eventually into the intake system. The crankshaft rotation throws oil to the right side (viewed from the rear) of the engine crankcase which causes oil to be blown up the drainback holes into the right side cam cover. The right side cam cover has the only breather connections on S4 & GT engines. This undoubtedly exacerbates the propensity for these engines to blow oil into the intake system when being run hard. The GTS engines have cam cover breather connections on both sides which may help. A sustained left turn is even worse with oil in the sump being forced to the right side.
We can make some changes to give better oil control with less oil lost to the intake, and provide better lubrication for the engine. I'll give examples of what I did, or plan to do. Other approaches may work as well, or better. Improvements should address three areas.
1. Both cam covers should have breathers.
2. Increase crankcase breathing capacity.
3. Provide effective oil control in the sump.
My plan was to supply fresh air to the cam cover breathers, install a larger crankcase breather outlet, and vent the blow by gasses into a vacuum source in the exhaust. I didn't use any of the stock breather system other than the cam cover breather fittings. The two 12mm outlets in the base of the oil filler were plugged.
1. Both cam covers should have breathers. A breather fitting was installed on the left cam cover in the rear hole. An oil control shroud was used under the fitting (inside the cam cover) the same as on the right rear breather fitting. The small passageway in the right rear breather fitting was drilled out to the same size as the front fitting. The front right cam cover breather was removed and the hole plugged using the plug from the left rear cam cover hole. The breathers were supplied with fresh filtered air from the air box below the air filter. This was accomplished by drilling holes in the air box and using a rubber hose to connect the breather fittings to the air box holes. Rubber grommets in the holes with the ID sized for a tight fit to the rubber hose insures a secure and dust free seal between the air box and hose. Now, the cam covers will receive clean air which will flow into the cam covers and down the oil drain back holes to the crankcase. This air will flush combustion byproducts out of the engine.
2. Increase crankcase breathing capacity. A vented oil filler cap was made using the stock cap as the interior to retain the threads and seal. An aluminum cover was constructed with a swiveling center to permit the cap to rotate around the vent line. The center part is made from brass and retained in the cover by an "O" ring. Illustrations are shown below.
Oil filler cap breather
Oil filler cap breather underside
3. Provide effective oil control in the sump. Nearly all the high performance engine building books I use recommend use of crankshaft oil scrapers, a windage tray, and a surge baffle in the oil sump. The books that don't recommend the surge baffle recommend instead that a dry sump oil system be used. I chose to stay with the 928 wet sump oil system to reduce cost, weight, and overall complexity. The design of the 928 oil sump is in some ways good, and some not so good. It's good in that the sump does have internal baffles and a flange of sorts around the sump edges to reduce the oil climbing the sides during high "G" cornering. Also, the oil pickup is in the center of the sump with a generous sized pickup tube and well designed inlet. It's not so good because it is much too shallow with insufficient distance between the crank counterweights and the oil. The pan floor is so close to the crank that a windage tray, or screen, can't easily be fitted.
Copyright 2004-2010, OTT'S PERFORMANCE ENGINEERING. All Rights Reserved.
Last edited by ptuomov; 05-22-2010 at 10:15 AM.
05-21-2010, 07:00 PM
#3
Nordschleife Master
Any info tying the video times to the corners?
Sure seems to spew foam more often than in just the lefthanders. I'm assuming the course was run clock-wise.
Sure seems to spew foam more often than in just the lefthanders. I'm assuming the course was run clock-wise.
05-21-2010, 09:15 PM
#4
Nordschleife Master
Thread Starter
05-22-2010, 03:47 AM
#7
Rennlist Member
Not just left handers , every time s4 the engine sees more thean 6K the heads will fill with foam as you are seeing on the video , this is even with a windage kit and the DR oil collector , so its not hard to see why they become terminal , I was going to try to create a vacuum in the sump with the DR collector , but after seeing the oil that overwhems it , thought that was a bad idea.
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05-22-2010, 10:31 AM
#9
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From the remarks on Youtube:
This is an extremely important video taken by Louie Ott of the interior of the cam cover of a Porsche 928 on a track back in 2003.
www.performance928.com is Louie's website.
In hard left turns the oil can be seen to be violently blasted up the oil return passages -- one of which would be to the left of the tappet. There is a delay that is approximately 5 seconds long (give or take) and the aerated oil in the shallow area of the sump and probably that oil which has drained down from heads makes its way to the sump. The highly aerated oil is drawn into the pickup tube and compressed by the pump. Typically oil can hold dissolved air at about 9% per bar pressure. The Porsche pump runs at many bars of pressure. When the oil emerges from the cam bearings (primarily) it releases air from the supersaturated oil like sodawater and this whitish-brown foam is clearly seen to be flung by the cam lobe onto the plexi-glas window.
This is direct evidence of the high aeration of the oil in the wet-sumped 928 engine in competition use. This high level of aeration is what kills the 2/6 bearings. They just happen to be the first to get a good sustained dose of it in these situations. The Porsche 944 engine has a similar failure mode for the number 2 bearing since the bed plate oil passages are arranged similarly. The 944 engine was derived from the V8 block in the 928.
This video is left unedited so that people can see the raw data.
www.performance928.com is Louie's website.
In hard left turns the oil can be seen to be violently blasted up the oil return passages -- one of which would be to the left of the tappet. There is a delay that is approximately 5 seconds long (give or take) and the aerated oil in the shallow area of the sump and probably that oil which has drained down from heads makes its way to the sump. The highly aerated oil is drawn into the pickup tube and compressed by the pump. Typically oil can hold dissolved air at about 9% per bar pressure. The Porsche pump runs at many bars of pressure. When the oil emerges from the cam bearings (primarily) it releases air from the supersaturated oil like sodawater and this whitish-brown foam is clearly seen to be flung by the cam lobe onto the plexi-glas window.
This is direct evidence of the high aeration of the oil in the wet-sumped 928 engine in competition use. This high level of aeration is what kills the 2/6 bearings. They just happen to be the first to get a good sustained dose of it in these situations. The Porsche 944 engine has a similar failure mode for the number 2 bearing since the bed plate oil passages are arranged similarly. The 944 engine was derived from the V8 block in the 928.
This video is left unedited so that people can see the raw data.
Tuomo noted in another discussion that the Accusump could be masking extreme pressure drops -- possibly to zero from the pickup being uncovered. I do not think the pickup is being uncovered but I do think that without the Accusump that the display of foam being ejected would continue longer or more intensely.
05-22-2010, 10:44 AM
#10
Nordschleife Master
Thread Starter
I think it's important to note that your speculation below is inconsistent with what Louis Ott thinks is happening. I am not picking a fight here but I don't think you can just go and insert your conclusions to someone else's research without a comment when those conclusions are inconsistent with the original researcher's conclusions. Or since the internet is free, you can, but don't expect not to be called on it.
From http://www.performance928.com/cgi-bi...s_parent=1128:
The highly aerated oil is drawn into the pickup tube and compressed by the pump. Typically oil can hold dissolved air at about 9% per bar pressure. The Porsche pump runs at many bars of pressure. When the oil emerges from the cam bearings (primarily) it releases air from the supersaturated oil like sodawater and this whitish-brown foam is clearly seen to be flung by the cam lobe onto the plexi-glas window.
The frothy oil was likely not coming directly through the pressure fed oiling system. It was probably being whipped by the crankshaft and was being blown upward through the oil drain back holes from the oil sump area.
05-22-2010, 11:08 AM
#11
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I think it's important to note that your speculation below is inconsistent with what Louis Ott thinks is happening. I am not picking a fight here but I don't think you can just go and insert your conclusions to someone else's research without a comment when those conclusions are inconsistent with the original researcher's conclusions. Or since the internet is free, you can, but don't expect not to be called on it.
From http://www.performance928.com/cgi-bi...s_parent=1128:
From http://www.performance928.com/cgi-bi...s_parent=1128:
There is a distinct qualitative difference in the foam in question as well as the timing of its appearance. The still picture shown on Louie's website does not show this later appearing foam. At this stage, after viewing the video with many, many instances of the foam and its delayed appearance, it is important to ask whether one has any form of color blindness as this will certainly affect its perception.
As you know from the other discussion I am more than willing to defend what I write.
Update: A link has been provided to Louie's comments and pictures. I tried to paste the whole shebang in there but Youtube said it was too long.
Last edited by Kevin Johnson; 05-22-2010 at 11:43 AM. Reason: Update on link to Louie's site
05-22-2010, 06:46 PM
#12
Rennlist Member
Yeah. we are going a lot faster, pulling more Gs and have 100s of hours on the 928 engines with no issues. mabye is the anti foaming characteristics of the amsoil. who knows. currently, still running the stock 928 with a stroker bottom end as the ONLY modification. (no accusump, pan spacers, scrapers, etc etc)
mk
mk
05-22-2010, 11:02 PM
#13
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Yeah. we are going a lot faster, pulling more Gs and have 100s of hours on the 928 engines with no issues. mabye is the anti foaming characteristics of the amsoil. who knows. currently, still running the stock 928 with a stroker bottom end as the ONLY modification. (no accusump, pan spacers, scrapers, etc etc)
mk
mk
Bill has a good suggestion -- why not rig up a camera and spot light on the same area that Louie did? Video cameras are dirt cheap now versus 7 years ago. THAT would be interesting.
Maybe you could synchronize it with that cam you use during the races?
05-22-2010, 11:44 PM
#14
Race Director
great thread
aerated oil is a serious problem and it directly contributes to our engine failures...it is one of several issues in the oiling system that only become apparent under track conditions...
Interesting that aeration is correlated to oil pressure....9% per bar is quite high...given that 928's run well in excess of 100psi or 7 bar....so up to 63% of the oil is foam? That can't be right
aerated oil is a serious problem and it directly contributes to our engine failures...it is one of several issues in the oiling system that only become apparent under track conditions...
Interesting that aeration is correlated to oil pressure....9% per bar is quite high...given that 928's run well in excess of 100psi or 7 bar....so up to 63% of the oil is foam? That can't be right
05-22-2010, 11:54 PM
#15
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Yeah. we are going a lot faster, pulling more Gs and have 100s of hours on the 928 engines with no issues. mabye is the anti foaming characteristics of the amsoil. who knows. currently, still running the stock 928 with a stroker bottom end as the ONLY modification. (no accusump, pan spacers, scrapers, etc etc)
mk
mk
great thread
aerated oil is a serious problem and it directly contributes to our engine failures...it is one of several issues in the oiling system that only become apparent under track conditions...
Interesting that aeration is correlated to oil pressure....9% per bar is quite high...given that 928's run well in excess of 100psi or 7 bar....so up to 63% of the oil is foam? That can't be right
aerated oil is a serious problem and it directly contributes to our engine failures...it is one of several issues in the oiling system that only become apparent under track conditions...
Interesting that aeration is correlated to oil pressure....9% per bar is quite high...given that 928's run well in excess of 100psi or 7 bar....so up to 63% of the oil is foam? That can't be right