glyn

Im preparing a 1980 euro spec 928S for historic racing in australia.Im plagued with the problem of oil getting into the combustion chamber at race speeds and race G forces. I have fitted breather pipe baffles and sump baffles but the problem persists. The detonation resulting from this problem has caused one engine rebuild and i may be due for another. As 928s are extensively raced in the USA a solution to this problem must have been found for it. Can anyone help with advuse or a solution or diresct me to someone who might be able to help
regards glyn crimp

Ed Ruiz

I understand that some 928ers have removed or replaced a check valve in the cam-towers so as to not pool so much oil in them at high RPM. I believe they use a lower setting check valve from either a 944 Turbo or a 968.

Another solution is the use of accusumps. They hold a bit more oil and provide it to the engine as needed. That may not help your problem, but it does reduce the chance of oil starvation that sometimes occurs with rod bearing 2&6.

Yet another solution is using Redline Synthetic oil. Apparently, its properties do not lower the octane of the fuel mixture as it is consumed in the cumbustion chamber.

I personally have not done any of these "fixes". Since I only do DE and Autocross and do not "race", I tend to not get the engine near redline for any extended amount of time. I tend to take sweepers in a higher gear and at least 1000 RPM below redline so that I reduce the chance of oil starvation to rod bearing 2&6.

I know others who have been tracking their 928s for over ten years and they have never had any lubrication problems. From what they've told me, they don't go to redline often either. YMMV.

John Veninger

Have you tried using a catch can? You do not need a closed loop breather system on early 928's.

Erik - Denmark

Glyn,
I think we have a common problem, see the following, I woud like to have your comments.
Regards from Erik in Denmark
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During a trip to Le Mans in France I damaged my newly renovated motor (20,000 Km) by driving fast 220 + Km/h (135 + M/h) during several hours in Germany and France.
I bought a 1984 car with a minor traffic damage from Switzerland with only 108,000 km on the clock, and installed this motor in my car.
The new motor is M28/22 with electronic injection (LH-Jetronic) and the old is M28/12 with mechanical injection (K-Jettronic)
Now I open the old motor:
Three pistons are damaged no 3,4 and 8 - I.e. the piston rings are broken, the upper one, broken into small pieces (down to 2 mm) and the pistons are broken in-between the rings in some places.
The cylinder no 4 has a tiny scratch, but not more than it will be possible to make a reasonable motor out of it (spare motor) if I get three new pistons.
No doubt, that's due to knocking (detonation).
In my new motor I installed the Devek modification (baffle) (standard from Porsche from model S4)- And I am now using Valvoline oil. (See the below Devek article)

Of course I want to find the reason, and think the theory from Devek can be the answer, but how can I be sure, and feel safe when driving fast in future?
I am very interested to hear from you if you have ideas or maybe same (bad) experience.
Regards from Erik in Denmark
928 S(2) - 1980/84 - Euro - Aut.

Copy from Devek technical support (You can see this on <a href="http://www.devek.net" target="_blank">www.devek.net</a>
The Devek theory:
Oil driven detonation: The 928's chronic oil lifting behaviour at higher rpms dumps oil into the induction system, causes smoke in the exhaust and, detonation of the engine at its peak output. That's because oil mixing with the injected fuel lowers the effective octane rating and hence the
detonation threshold. Detonation damages pistons, valves, and rings, and forces rebuilds before the 928's 200,000+ mile engine life has been ttained. Some racers use two-cycle engine oil in the crankcase because that oil is formulated to be burned and is specially blended to be compatible
with fuel.
The Fix:
Install DEVEK's oil control modifications at the next engine disassembly.
At the next oil change, fill with Red Line or Valvoline synthetic oils. Porsche tested a broad range of oils for fuel compatibility and found Valvoline synthetics to reduce detonation when mixed with fuel and burned in an internal combustion engine. The Red Line synthetic oils are
blended for compatibility with the higher octane fuels recommended for
Porsche engines.

techsupport@devek.net


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Posts: 6 | From: Denmark | Registered: Apr 2002 | IP: Logged