hairywithit

Rob Edwards

This was BEFORE I disassembled, so pretty sure the cam caps are in the original positions:

Lizard928

Greg,
Thank you for sharing the rest of that info.

With regards to the 1.5" pipe out of the crank port, I put it on the passenger side pushing down into the block. This required a slight pinching of the pipe to slide in. I cut it at a 45 deg angle to help knock the oil off first.
I then put the pipe at a 90 deg angle and ran it down the back of the block and put the filler/canister with the scrubbers in it there.
As well I have tried a number of different materials for insertion to help drop the oil. Copper kitchen scrubbers worked the best.

Now this is on a strung 4.7L. You have much larger bores which of course is going to lead to a much higher volume of air having to move.
So that pipe may not be enough. However this car and my car have been run from roughly 80/100kmph up to 240kmph with zero oil injection present.

I would be very interested in how much oil was ejected from that hose during the run made.

The other thing I would be interested in hearing is why you believe the 944S2 valve would not provide enough oil at idle. That head and cams are pretty much exaclt the same as the 928S4 head and I have not heard any issues with excessive cam wear.

Do you have any other ideas and thoughts as to why to oil is not exiting the heads? With both sides filling up, I think we can safely rule out the problem being caused by the whipping in the crank. The only thing left is an excessive flow of crankcase gasses.

Darklands

@Greg,
I ask my friend Jochen here in Germany and he´s the owner of the shop here who build probably the most 928 engines/year.
He told me he has the same symptoms like you with one customer GTS engine.
Over 5000 rpm the engine blow oil just like yours.
The conclusion was wrong rings.The customer buy the rings by himshelf and took 944 rings.
All symptoms after changing the rings to genuine 928 rings gone away.
He told me optical are the rings the same but what´s with the mixture?Are you using 968 piston and rings in the 928 block?
Is this a gts block with more holes for venting in the block?A stroker has more problems like this as a stock engine.
So are you be sure you haven´t build an air pump?
I´m a farmer and a 928 fan but not an engine builder.
I hope you understand my post as a hint in a new way of thinking and not as a personal attack.
English isn´t my native language and I think I can tell you this in german a lot better.

This is a very interesting thread and I wish you to find the solution of your problem quick.

MattCarp

I find Colin's experience pretty interesting.

Where's the best place to get a good description of how the stock breather system works?

The best I could find is Mike Schmidt's writeup, posted on Louis Ott's site:

http://www.performance928.com/cgi-bi...ss_parent=1128

As Mike says there, "it's a lot easier for me to explain in person than in writing".

If there were a just a couple diagrams or pictures, I think I'd be able to follow it...

928er

I think the next test should include pressure sensors in each cam cover as well as crankcase to determine if there are differences in pressure or vacum to show the oil drain ports as a restriction. If they are restricted there should be a pressure difference between the heads and the crankcase.

It would also be benificial to use modified cam covers like louie's so that it can be seen what is happening inside the heads. Combine this with clear tubing on the vents and the pressure sensors it would be a good data point.

m42racer

These threads are great. We can all be arm chair engineers with all sorts of ideas. But the best part is we don't have to pay for it......yet.

BC

Would scraping the oil from the crank throws help any of this or would there still be this cloud?

What about the drains on the side of the block from the heads. The scraper guy had shields so they would not point the oil at the crank.

I took out my scraper. The reason is I am concerned about piston oiling.

hacker-pschorr

Does anyone know, what modifications were done to "The White Car" DEVEK built as far as the oiling system is concerned?
As far as I know, that engine is still alive and well in open road racing.

928er

Greg,
Has a leak down been done on the engine yet? On my 1st stroker engine, I had some oil ejection issues, but then I found out that I had some huge leakdown numbers.... the numbers were bad enough that I elected to pull the motor apart..... new engine doesn't have the oil ejection issues nor does it have the blowby that was in the 1st engine.

Mike Simard

I happen to know that on a nice dry sumped engine, the valve covers will fill with oil after a long straightaway.
Blowby is a bad thing but not the cause of the valve cover full-o-oil IMO, at least not in my case.
After that experience I did a drain modification to the block and suspect it's much better now. Another change I made was to spin the scavenge pumps faster in the hopes of holding higher vacuum.
Extended full throttle does more things than you could ever have imagined, it's a whole 'nuther world from chassis dyno pulls. In the times I've been in my car and dared to peek at the gages (including crankcase vacuum) on a long straight, it's always a surprise at some level.

hernanca

When I read it, here is what I had come up with from Mike Schmidt's excellent write-up.

Mike would need to verify it for correct interpretation, however.

Mind you, this is my interpretation of Mike's interpretation of the system..

I used Dave Robert's stock layout diagram from his SharkVent page as a basis (I hope that's OK, DR!).

If anyone wants the source Visio file, I can e-mail it to them.

svp928

Brendan, even with scrapers, there is constantly a flow of oil from the sides of the rods and mains being flung up into the bores, so oiling the pistons should not be a problem. The scrapers just help knock off oil the crank picks up or spits out as it swings thru the pan.

The basic problem here is pressure in the crankcase is greater than pressure in the heads, causing oil and air to flow the wrong direction. Some of this as natural- if you watch the pistons move up and down as the crank turns, you see that the two pistons on each throw create a big volumetric change in the crankcase as they go from TDC to BDC. Consider that in one full revolution, the volume delta displaced by those two pistons is 50% of the engine's displacement...This volume of air gets moved around in the pan in a wetsump engine. Because our pan is small, some of the air tries to go UP the return port to head as the pistons on that throw move toward BDC. Complicating this is our 90deg V-8, where the air wants to go from the front to the back of the engine, while the two sets in the middle are trying to swap air. You can see, at 6000 time a minute, air traffic gets congested..... Obviously, a bigger engine has a bigger problem. Sadly for us, that small pan means no amount of scraping or windage trays will solve it completely.
Evacuating the air from the crankcase is the only way this can be overcome- a drysump engine does this naturally, and current engines have each pair isolated completely so no air moves around in the pan... On a wetsump, some form of vacuum pump is needed if the engine is going to sustain high rpms for any length of time, and there still may be a need to scavenge oil from each head.
Greg is working on this, and it won't be easy..!

txhokie4life

So if I understood what Greg said in his response to me was that
the air pressure difference is a symptom not a cause.
The cause is believed to be the inability to drain the heads quickly enough
causing the "drains" to clog, which in turn causes the air pressure difference,
which just reinforces the situation.

So the question that comes to my mind is does addressing the air pressure
just resolve a symptom?

If the inability to drain is indeed the problem, at some point you will not have anything
to fill the heads with (in the extreme) and if the pressure delta didn't exist -- it would
then be able to drain of you could "compartmentalize" the process.

Does the channels need to be larger -- or secondary paths need to be created?

Has anyone calculated the volumetric flow required? Are there structures of the paths
that allow for better flow (sort of like laminar vs turbulent air flow - roughing up the surface
actually induces faster airflow by creating a turbulent surface to ride upon - the old golf ball design)

I'm sure its not as simple as breaking the problem down into distinct parts.
But that's all my feeble non-mechanical brain is capable of processing?

mike

GregBBRD

My mistake...that was the exhaust cam.

There's a bunch of oil there. Too bad that the rpms and load were not recorded, at the same time. Irregardless, it is an interesting video.