928er

either that or the oil deflectors cause the oil to drain slower in that head making the problem worse...

So here is a question... I added a sharkvent system and it drastically reduced the amount of oil that my stroker engine was burning.. however the insides of the provent seperator show that very little oil is actually making it in there. I do plan on plumbing all 3 of the plugs in the V to the shark vent system when I go to ITB's

Lizard928

We also eliminated this as a possible suspect when Greg B stated it came out of both heads at the same time.

The more I think about this, the more I think it would be a very wise idea to install some cam covers onto a motor without any breathers. But to install a couple of "windows" in the covers to see as to where the oil level is.
Then to simply vent the sump via the largest pipe and air/oil separator possible attached where the oil filler is.

This would tell us 100% if the oil in the head is being held there because of design/volume, or if it is being held there because of airflow.
I am more inclined at this time to believe the earlier. Simply because of the size of the drains vs. the size of the cam breather holes.

928er

one thing I noticed about the block is that the oil drians restrict from the opening size at the top to the opening size at the bottom by almost half.....I'm guessing this was due to casting technology.... could these drains be opened up a bit?

killav

Greg,

I have already fabricated another extension so both breather outlets on the drivers side cam cover will have a breather elbow and extension. I managed to find one stock used extension and had to make the other. My car has been apart now for two weeks mainly because of this timely thread. It has stopped me in my tracks while everyone is brainstorming trying to find solutions.

This thread should be stickied to the very top from now on. By far one of the most important threads next to TBF that any 928 owner should read.

GregBBRD

The heads are going to still fill with oil and the sump will be run low. This is a primarily a volume issue and a windage problem secondary.

I'm pretty sure that if you check, people have lost engines with that system installed.

GregBBRD

Note that I got oil ejection from all four breathers at about the same instant....this problem is happening regardless of crank rotation.

GregBBRD

Mike:

Note that I've been doing this, for quite some time, in my engines (I used four "extentions" in this engine...two of which were custom made to fit into the smaller head opening. All four had "internal" changes to separate out oil/air.) I believe this modification allowed me to see this problem a bit earlier than normal. Otherwise, I would have just lost oil pressure and not known what the real problem was....like has been going on for 20 years.

I thought I knew what I was looking for...but change allowed me to see it happen.

GregBBRD

True. This block even has casting "flashing" around the holes that come straight down. I was going to remove it, but because the other side isn't remotely the same (it makes a crazy 90 degree turn to exit) I figured that this was not going to solve the problem.

Plus that, this would be hard to do and a mess, on an assembled engine.

I even thought about drilling another hole into these drains, closer to the top of them...to give the pressure/oil another place to escape. Just could not make any sense of this. If the crankcase gets pressure, from the drains covering up, the pressure would be the same on both the original opening and any additional opening I might make. That still blocks the return and allows more oil to collect in the head.

Let's not forget...the Porsche engineers are not stupid...and they had to know what happened when these engines were run hard, at high rpms. They have dynos and use them. If there was an quick/easy solution, I'd think they would have done it. Certainly, the addition of the GTS windage tray was an effort to keep the crank from picking up oil from the sump and keep that additional oil from being "thrown" up into the crankcase breather. This is probably why they only used the "oil squirter" blocks for part of the '87 production run. They probably saw that spraying oil at the pistons only put more oil up into the crankcase and took more oil away from the sump.

I'm guessing that this oil problem might be one of the primary reasons the Porsche factory didn't want these vehicles raced.

IcemanG17

There has to be a serious reason why they didn't do it..... They raced plenty of 944's with essentially the same engine design....

john gill

Yes I agree with you 100% GB , my answer was to Johnse in responce to filling of the 1 to 4 head as I have oil comoing out of both , however it would be interesting note that is the problem worse or better with the scraper system installed.

I am about an hour away from the dyno to conduct some pressure differntial testing .

I will try and find some stock cars to compare results with as mine is obvoiusly modified . So anyone listening to this locally feel free to make your car available .

I wonder if removable ears on the sump could be installed , to increase the volume of the oil , again this is something that was done in the old group c race cars here years ago .

worf928

The other night I was looking at a short block I have here and had a similar thought. There's a lot of "meat" around the head drains. I haven't measured but I suspect that taking out a millimeter of the meat all the way around would increase the area by a significant amount with a similar increase in drain speed?

If the crank case was - in addition - vented elsewhere, might the two changes in combination allow just enough oil drainage?

928er

That is exactly what I was thinking. Open the drains, & vent from the V or from the oil filler neck in addition to the heads, just to make sure that no additional pressure builds up in either. Of course this is only an option when you are building an engine. I can't imagine that opening the drains would be a bad thing in any way. These in addition with a check valve that is maybe halfway between the stock oil check valve and the 944 S2 check valve might be enough to do it.... small changes in the way the oil is fed to the head, as well as small changes to the oil drains might just be the ticket....

I honestly think that the oil packing issue is a combination of several different problems. Each problem has a solution that is part of the bigger picture.


This thread alone has identified 2 known issues:

1. Excessive crankcase pressure
2. Inadequate cylinder head oil drain passages

This could be why engines have failed with other oil issues addressed (ie: Windage, which is known to be resolved in other engines with the use of crank scrapers, & crank oil flow problems resovled by drilling like a chevy)

This brings me to wonder what would happen if we had all of these in one engine?

Crank drilled like a chevy
Oil drain ports enlarged
cylinder head check valves modified
crankcase venting from block in combination to heads.
Crank scraper for windage

Poreche very well could have known about all of these issues and their solutions, but for financial reasons didn't see the benefit in modifying production on so many parts. Not to mention that most of these issues would not come to light in many cars on the street. It is cheaper to just recommend against racing... which they could get away with for quite some time as the cars were heavily equiped and expensive.... they weren't exactly marketed towards the racing crowd... more likely targeting Mercedes SL owners....

worf928

The other wacky idea I had was to use the exhaust cam "plug" at the back of the head as a means of draining the head. But, there isn't a lot of room back there and the heat from the exhaust would limit routing options.

My observations of the Shark Vent system in several cars is the same as yours: oil usage drops but the separator is dry. That suggests that the primary effect is dropping the pressure in the crank case with the secondary effect of not pumping aerated oil back through the intake. However, it is known that at sustained high rpms oil gets pumped into the separator. Thus, my thinking the faster drainage might help in combination with crankcase venting.

I suspect Doc Brown's right though, about there just being way too much oil thrown into the heads at high rpm. If true, the proper way to deal with it would be to deliver oil to the heads non-linearly with increasing rpm. But, without factory money that probably isn't as practical as simpler solutions.

928er

That is why I'm saying that a multi faceted soltution is in order. If you could increase the drainage by 20% and dial back the oil by 15% you would see some benefits. All we have to do is overcome the excess oil enough to run the engines to specific RPM's.

blown 87

As some one said, maybe they did not want a 928 out running the 911's.