Fastest928

...damn...did it again!

Oiling facts:

1 during a test at laguna in 1995/96, using mobil 1 at factory recommended fill volume, turning 1:44's laps, showed repeated fluctuations - drops in oil pressure using a stock crank running at 6000 rpm.

2 dyno test to 8,000 rpm for 30 seconds using a stock crank and modified chipset using factory filled crankcase showed fluctuations in oil pressure at 3-6 seconds

3 disassembly of the above engine showed unusual wear patterns on 2/6 rod bearings vs other journals. all journals had "rpm" related wear

4 same laguna test #1 performed with drilled crank..same oil pressure drops

5 same test as #2 performed, same drops

engine not disassembled, oil tested ok

6 install devek race accusump system

7 #1 laguna test performed, no oil fluctuations

8 # 2 test performed again, oil fluctuations occurred later in test 10-14 seconds

9 engine disassembled and bearing checked....some wear on 2/6 bearings

10 two known 2/6 rod failures in GT by driving at or above 5500 rpm for over 100 miles through sweepers. engine oil level unknown.

11 many 2/6 rod failures in track driven 928s

12 known failures using an accusump...one not turned on and the others not installed correctly and too small a capacity...now you know why we choose the 3 qt vs a smaller size.!

13 Porsche AG purchased DEVEK race level accusump for 928 racers after repeated failures of customers racers....no recorded failures since installation

Conclusion:

2/6 failure at normal rpms is due to oil starvation, not crank oiling pattern

the hotter the oil, the faster the onset of starvation

if you are spinning it ot over 7K rpm, drill the crank

DEVEK 3 qt accusump system will allow for more time before onset of oil starvation. If you are using slicks, use the race level system.....

dry sump will eliminate starvation forever, regardless of crank, unless you exceed 7000 or so rpm, then you need revised oiling pattern...also, a well designed dry sump will add 7 or so hp per liter...hmm, in a 6.5 that makes close to 50 hp...

Porsche designed an excellent street engine......the reason why GT and GTS fail "more" often is the average revs are higher, thus more oil is pumped and "aerated", and less is available to be pumped to the bearings.......And in Germany, running at 170 ish on the bahn, the revs are high, the oil level in the crankcase is low and up comes a high speed high "g" corner...and a potential oil starvation situation.....a condition they did not take into account.....well enough.

Things you can do to minimize the situation:

1 keep the oil cool
2 run high grade synthetic...cost more, but change less...amsoil, redline, etc.
3 if racing, use race level accusump
4 if building a racer from scratch, use dry sump and gain hp

maybe more on crankcase venting later...

Marc
DEVEK

Nicole

Thanks, Marc! Very interesting information... I will post a link to this on the German PFF board.

One question, though: If there would be a condensation reservoir that catches the oil, rather than having that oil "fog" go directly into the intake, that oil from the reservoir could be directed back into the oil pan. Wouldn't that be a relatively simple way to reduce oil consumption in some of the later engines when they are driven hard? It sounds to me like a rather not-so-complicated (meaning affordable) solution that might help lots of owners. Would this issue be irrelevant, if you have the accusump?

GlenL

The problem with re-circulating the oil is that the blow-by that carries it out contains a lot of water vapor. What comes out of the catch tank varies a lot with engine health and use. My experience was that in heavy track use it looked like mostly oil, but with some water. In street use the collected fluid was very watery with little oil.

I think the best solution is to reduce blow-by from the rings and then disconnect the PCV system and run that to a tank. That way your not forcing or sucking the oil mist out.

Jim bailey - 928 International

The facts that I look at most are that the stroker crankshafts (Scat "DEVEK", Moldex ) are made to feed oil "Chevy" style so that 2-6 get oil from the main journal behind them . Kim Crumb has had 2-6 failure blown up his GT engine twice ? His old Project 928 85 Euro had 2-6 catastrophic failure at the first track event after he sold it ! nearly cut the block in half . Ed Ruiz GT engine , Don Hanson GT engine , David Lloyd 5.0 hybrid (also 4.7) . Joe Fan lost a S-4 engine 5 liter . The list goes on and on . Yet I am not aware of any stroker engine (Chevy oiling) which has had 2-6 bearing issues BUT I do not hear about all the stroker engines mostly just our engines . There is no doubt in my mind that dry sump oiling is the proper way to manage oil pickup , windage / blow-by as this is how Porsche fitted all aircooled 911 engines . Even current 911 race engines are dry-sump by the factory , all top Nascar engines are dry sump . Mark Anderson's engine is dry sump , Bob Devore ran his big engine dry sump . Fitting an accusump properly plumbed adds another couple quarts of pressurized oil which may give you a few seconds of pressurized oil when it needs it most . It also may cause you to run the oil level higher depending on how and when you check the level since the amount of oil in the accusump varies depending on the oil pressure at the time the valve is closed . So like it or not the 928 engine does have a basic design flaw ..... corner hard rev it much over 6,000 and as Kim Crumb pointed out some 12 years or so ago ........you will burn up 2-6 rod bearings , by his calculation after 10-12 track hours .

Doug Hillary

Marc,
Could you expand a little on your post please

Oiling facts:

Your 1
a) What blend and viscosity of Mobil1 oil was used.
B) Was the oil new or had it been used for some time
c) What is the "...factory recommended fill volume..."?
D) What were the "...drops in oil pressure..." in actual numbers

Your 2
a) What is meant by "...factory filled crankcase..."?
B) What fluctuations in oil pressure "...at 3-6 seconds..." occurred in actual numbers
( I presume you mean after 3-6 seconds )

Your 3
a) What is meant by "...unusual wear patterns on 2/6 rod bearings..."
a) What is meant by "..."rpm" related wear"

Your 4
a) What were the actual "...oil pressure drops"

Your 5
a) As for Your 4) above
b) "...Oil tested OK..." What testing was done on the oil, by whom and what were the actual test results

Your 8
a) What "...oil fluctuations..." actually occurred?

Your comment:
"the hotter the oil, the faster the onset of starvation"

a) What is really meant by this (parameters) ?
B) What oil temperature/starvation data exists

Your comments;

"Things you can do to minimize the situation:

1 keep the oil cool"

a) At what temperature?
B) How?

"2 run high grade synthetic...cost more, but change less...amsoil, redline, etc."

A) Are these "high grade synthetic" oils" ( Amsoil, Redline, ) and what criteria is used to decide this
b) What oil is meant by "...etc."?

Thanks

Fastest928

Doug,

In general, the drops in pressure were down to 2-3 bar in almost all cases. Of course, from what pressure they dropped is unknown, just that it was above 100 psi....the max of my testing gauge.

Crankcase fill is top line on level ground with engine oil at operating temps.

Hope this helps,

Marc
DEVEK

Nicole

Latest news from the German discussion board: Uli writes that the red race car was fitted with the original DEVEK AccuSump system, which he highly recommends. This system has done great and he sends his "thanks and greetings" [to the DEVEK team].

However, he says they went a different route to ensure lubrication of the rod bearings #2 and #6. He offers to make the modification for Euro 350.00 (about US$400) - all you have to send to him is the lower bearing block - not sure what he means by that, but I'm sure you guys can figure it out.

Now I wonder how long it will take until someone in the US will license his solution/procedure and make it available to the racers over here.

Uli's email is "lupino-us@t-online.de"

drnick

in practice how high do stroker motors rev? also, what performance gains are their in raising the redline significantly, with an appropriately drilled crank?

my old s2 with over 160k does use some oil especialy when driven higher in the rpm range. i spent last weekend hitting the rev limiter in 2nd and 3rd gears (auto trans) at somewhere near 6500 on the tach thinking about a higher output engine that revs a bit more! after that trip the engine oil needed an extra litre... im glad i checked it when i did.

Fastest928

Nicole,
We did some modification to the main oil galley by adding some flow restrictions, but it was found to have little effect on oil flow in engine.

Nick,
Our rev limit is 7,000 rpm

Marc
DEVEK

BB928GT

Hi Jim,

I second your point regarding the design flaw. At least that is what I gather from the pff-online.de discussion board.
Since I am not sure if all findings of the two pff-online threads have come accross, here again a summary:

The fellow who claims he has found and successfully solved the problem calls it a flaw in the (oiling) system (Ölversorgungssystem..( Systemfehler )). He has a pretty high cedibility within the forum and to me appears to be knowing what he is talking about.

He says that all the so far discussed measures would fail to address the 'really big problem'. He states the even the cross drilling of the crank shaft would only alleviate the problem but not solve it.
(Accusump or dry sump will ofcourse help on the cornering problem but obviously not on the 2-6 oiling problem especially at high revs.)

As Nicole reported he offers to do the modification for Euro 350. So it obviously can only be a small modification to the engine block, may be some hole or whatever...
Still since he burned a lot of his money in finding the cause and really solving the problem, it may be wiser to license the measure in order not to end up the same way...

I hope this helps to get a clearer picture.

Greets from Germany,

Bernd

P.S.: Still not sure if I should upgrade my block...

>>>>>
Key posts from thread 1:
alle bisher hier angesprochenen Probleme sind nicht wirklich das "ganz grosse"...bzw. kann man eher als "kleine Übel" bezeichnen..

Am eigentlichen Problem , und dies wurde noch nicht einmal von den Ing`s und Dipl.Ing`s der PAG erkannt,...gehen alle diese Massnahmen vorbei..
Auch das Devek Verfahren ( Kreuzbohrung der K.W. ) lindert nur begrenzt..

Accusump..hilft nur bei hoher Kurvengeschwindigkeit ...ist als Ergänzungsmassnahme aber sehr wichtig...

Das Prob. Nr. 1 ist aber die gesicherte Ölversorgung aller Lagerstellen auch bei Drehzahlen über 6200 1/min ...und da liegt der sprichwörtliche Hund begraben...

Lagavulin

Thanks BB928GT for taking the time and sharing with us!

Boy, I would find it hard not to, especially if I were a racer or drove on the AutoBahn.

Fastest928

Nicole, Brendt,
I am intersted in having a discussion with the individual who had identified the really big problem and compare notes. Does he speak english?

Marc
DEVEK

mark kibort

Amzoil 120 race days, no failure (knocking on wood still)
30 race days on the Holbert S4, running much faster than the white car has ever run at laguna 1:40.2 vs mid to high 1:40s in 1995.

My feeling , as most of you know , is that the mobil 1 is the problem. we will know for sure when Bill Ball refills the oil and tells me his rpm hot for 5 bar!. I think most falures are engine related and user related. Or, am I just lucky?? I have 100s of hours of video of my race car, on 100degree day, at the end of grueling races, and you can see the oil pressure pegged at 5 bar at high rpms, even on long duration left hand sweepers. (it Thunderhill) as well as buttonwillow, high duraton right hand sweepers at 5-6k and high g forces. just checking my video out last night to check for something else and was looking a the oil pressure guage. the only car that I have driven that fluctuated oil pressure was the one with mobil 1.
Fact or fiction???
Mk



keep the revs below 6100rpm, shift smart, and dont bang the rev limiter, and keep the oil at the full line.

If you can afford it, get the accusump.

Tony

eh...you'll blow it up at Hallet Kibort, trying to keep up with everyone!

Nicole

I posted on the German PFF and asked Uli to repsond here or directly to Marc - providing he speaks enough English to do so.