928 Maniac

Which is best? My wrench tells me the accusump system is not a cure.

How is scavenging done on a dry sump on a 928?

Where can I find online info / advice?

Thanks in advance guys.

Mike Schmidt

The dry sump is better for a couple of different reasons. It is more expensive and involved to install though. Mark Anderson from 928 International has a dry sump system installed on his race car. You might be able to get some information by getting in contact with them.

928 Maniac

Thanks Mike. <img src="graemlins/burnout.gif" border="0" alt="[burnout]" />

Mike LaBranche

Mr. Maniac...

My wrench agrees with your wrench. Says the bearing problem isn't from lack of pressure. He believes it's oil temp. Under extreme conditions, oil temp soars and starts to fail to do it's job. Keep it up and pretty soon you're listening to a bunch of steel rattling around inside an aluminum box.

Dry sump is extremely cool stuff. El mucho dinero tho. I would verify that you're stock oil cooler is working well or install an additional cooler with plenty of airflow along with a temp gauge.

It would be extremely interesting to know what oil temps were on the cars that have spun 2/6.

Mike LaBranche
84S, black/black, AT
83 EuroS, weinrot, 5spd

John Veninger

[quote]It would be extremely interesting to know what oil temps were on the cars that have spun 2/6. <hr></blockquote>

Dave Lloyd spun a 2/6 and his temperature was in the 230's I think.
Drilled crank is the only way to prevent this. Mark Anderson spun the 2/6 with a dry sump system!
Keeping the oil topped off and shifting under 6K seems to be the answer for stock cars.

Most (including myself) run their track cars with a drilled crank and an Accusump. Dry sump would be nice, but major $$$.

Ed Ruiz

Unfortuantely, I have to concur. My oil temp was not that high, but neither was the oil level. Shifting near red-line and briefly becoming airborne (negative Gs) didn't help. <img src="graemlins/c.gif" border="0" alt="[ouch]" />

From now on, I'll shift below 6k and keep the sump as full as possible (at least 8 quarts if not a bit more). YMMV.

Mike Schmidt

Most of what I'm going to say is speculation on my part, so keep that in mind, but oil temperature is not the problem. I don't think that the oil pump pickup being uncovered in a turn is the problem either. When I had my oil pan off I did some experimenting and found that another problem occurs way before the pump pickup would be uncovered. The pump pickup is located in the center of the symetrical pan. If the pickup being uncovered was the problem, the 2/6 bearing failures wouldn't be occuring primarily in left hand turns. The problem appears to be oil foaming.

Louis Ott cut a hole in a valve cover and fitted it with a clear plastic window. A video camera was mounted to view through the window, and the car was taken out on the track. Everything was fine until the car went into left turns. When that happened the nice steady stream of oil turned to foam. This was even with an Accusump on the car. He has since found that his 2/6 rod bearings were almost completely gone, and is now rebuilding the engine.

What's apparently happening is that in a left hand turn the oil surges to the right side of the pan, and runs out of the sump and up unto the flat rear portion of the pan. This occurs way before the pump pickup is in any danger of being uncovered. The rotating assembly comes surprisingly close to the that upper part of the pan, and probably dips into the oil when it runs up there, whipping it into a foam. Because of the direction of rotation of the engine, the rotating assembly helps to keep the oil on the right side of the pan. There are also angled ribs molded into the upper flat portion of the pan to aid in getting the oil to move forwards into the sump. Those ribs also move the oil to that right side. The oil pump continues to pick up oil, but it's foamy oil.

There's probably no great loss of pressure indicated because there is pressure. It's just that it's a combinmation of oil and air pressure, in the form of the aerated oil being pumped. If you had 100psi of air in there and not a drop of oil, your oil pressure gauge would show 100psi. It doesn't know the difference between oil and air, it just measures the pressure. The 2/6 rod bearings appear to be the most suceptible to marginal oiling, so those are the first to go.

The GTS baffle does nothing to keep the oil from running up unto the rear portion of the pan. After taking a good look at things, giving it some thought, and experimenting a little, I think that the main reason for Porsche putting the baffle in the GTS was to help reduce windage and oil consumption through the breather system in the GTS. With the longer stroke of the GTS, compared to the 5.0 liter cars, this would have been more of an issue.

When I had my oil pan off I made a baffle to cover the entire sump area, with only a hole in the center for the oil pump pickup to fit through. That made a big difference in how far the oil can surge up on the right side before it runs onto the rear portion of the pan, and be affected by the rotating assembly.

I think that adding extra oil to the engine may actually help to make the problem worse by causing the oil to run up on the rear portion of the pan even earlier.

Randy V

Great investigative technique by you and Louis to determine the root cause of the 2/6 rod bearing failure, Mike.

Is drilling of the crank therefore not necessary if you can control the foaming problem by installing a baffle?

Mike Schmidt

I wish I knew. Personally I don't think that drilling the crank really has that much of an effect on the bearing problem. It *may* help get a little more oil there, but it would still be foamy oil. A dry sump system would be the best way to go, because there's no oil in the sump to get whipped into foam. There's also a large oil reservoir so that any air in the oil there would separate more easily. At this point all I can say for sure is that there was oil foaming on Louis' car during left turns even with the Accusump.

Louis is doing his engine rebuild, and is going to put a full baffle like mine in at that time. I'm sure he will take another video to see if the foaming is still occuring, but I have no idea of when he'll be that far.

Here's a picture of the baffle I made. The smaller hole in the baffle is for the oil dipstick to go through, and that indentation is for clearance for the oil pickup tube. There's a turned down lip on the edge of the big hole to help prevent oil from sloshing up through it. *IMPORTANT NOTE*: If anyone ends up making one one of these, and puts the turned down lip on the large hole, you need to either cut the top of the oil pickup down some or drill holes in the side of it. If you don't, and you make the hole close to the diameter of the oil pickup, the oil won't drain into the sump fast enough.

John Veninger

Mike,
Nice work on the pan
I understand the theory on foaming oil, but then why did Mark Anderson toss the 2/6 on his dry sump motor? It wasn't until he drilled the crank that he stopped his 2/6 issue.
Maybe your pan design and under 6K shifts will be a good fix for those not doing an engine rebuild.
Is Louis putting in a drilled crank on his motor?

Randy V

That's some fine craftmanship there Mike - right down to the perfectly placed dipstick hole!

Mike Schmidt

Thanks for the compliments on the baffle. I'll be plenty happy if it works as good as it ended up looking.

I could very well be mistaken, but I didn't think Mark Anderson had ever had a 2/6 bearing problem with the dry sump system. Are you sure it wasn't with an Accusump? I thought that he had the cross drilled crank before he even had the dry sump system.

If the cross drilled crank was the solution to the bearing problem, it would mean that the problem was RPM related. From what I've always heard, left turns are a common factor in the 2/6 bearing failures. If it was just an RPM issue, the engine wouldn't know or care if the car was turning left, right, or going straight. There have been also been 928 engines without the cross drilled crank that have been run on the dyno at over 8,000 RPM, without the rod bearing problem. If the problem was just because of the crank not being drilled, it should have been the most obvious then.

If it wasn't for the video camera observation of the oil foaming during left turns, I might have had at least a little easier time believing that drilling the crank was a major factor in fixing the problem. I'm sure someone could take some measurements and calculate the centrifugal force on the amount of oil that's in the rod bearing's oil passage. I have a hard time beleving that 5 bar or more of oil pressure wouldn't overcome that centrifugal force though, and keep the oil flowing to the bearings. Again, all I can say for sure is that Louie had oil foaming, it was only in left turns, and his rod bearings were bad.

Louie is building a stroker motor now, so the new crank will be a drilled one as far as I know. Drilling the crank definitely won't hurt. I just don't think it really corrects the main cause of the rod bearing problem.

Some professional race teams dyno test their engines tilted to the side to simulate high G-force turns. It would be nice to be able to test a 928 engine that has a viewing window in the oil pan like that.

John Veninger

[quote] I could very well be mistaken, but I didn't think Mark Anderson had ever had a 2/6 bearing problem with the dry sump system. Are you sure it wasn't with an Accusump? I thought that he had the cross drilled crank before he even had the dry sump system.<hr></blockquote>

I'm sure. His took out the 2/6 with a dry sump, not Accusump. He did the drilled crank and that ended the problem. He now runs the drilled crank, dry sump and does 7K+ shift sometimes.

Mike Schmidt

I know that drilling the crank should help get more oil to those bearings, but I don't see how it could possibly help with the oil foaming. It'll be interesting to see if the foaming still occurs after Louie gets his car back together.

Besides the baffle, to help with oil control I put in a crank oil scraper and modified my breather system. My main thought for trying to eliminate or reduce the foaming was the baffle though.

Fastest928

Bob Devore built the first drysump 928 engine back in the mid 80's....using the stock pump and a pair of scavenger pumps to feed the tank...other use the same methodology as Bob...he gets the credit on this one.

Wd have a good understanding of the 2/6 oiling situation and concluded that the primary reason for the 2.6 being ghe first to fail is that it is the first galley to see the air stricken oil resulting from partial pickup. this is a part of the problem, but not the main cause of the failure. There is also a sever pressure drop in that journal, which is also a contributor when oil pressure is low regardless of oil aeration....generous engine clearences.

He and I also did a alot of work on how to use an accusump successfully in racing conditions.

Our racing setup has been used by racers for years and was purchased by the factory for factory assisted 928 racers in europe. It is also used by Don H and others, But it has to be used correctly.

There is also a street kit, that Louis used, however, his failure may have begun long before he installed a accusump.

Accusumps are very dependent on il temp, oil level, g's and kit choice. The race kit ONLY allows oil to flow forward and the street allows the oil to flow both ways....forward to the galleys and backfilling hthe pump. The race kit offers up to twice the protection ove the street kit.

Mikes pan "shroud" is interesting, but I think that there is a possibility of increasing the oil cloud due to proximity of the oil on "top" of the shroud to the crank.

In all cases, it requires a test protocol...we used Laguna Seca on race rubber monitoring oil pressure at both the accusump output and the oil pump output on a right left banked corner and produced the following results ....the stock oil pressure fell fast and the accusump pressure reduced gradually over time. The key is over time...it is not a foolproff solution but a good bandaid.

If you want a sure fire bet, use a dry sump.
Marc
DEVEK