GlenL

The spacer is valuable because the crank is too close to the pan. Add in the front sump and it's perfect for running liquid oil into the rotating assembly. A big design flaw in the engine. Something that tells me they didn't consider driving the thing on the track and reflect the clean sheet of the 928.

Starting with the oil a half quart low seems to have a good effect in reducing ejected oil. A number of racer and tracksters have reported that. The last half quart is ejected in the first few laps. I found, before adding the I-J setup, DEVEK oil filler plate and catch can, that starting up to 1/2 quart low didn't alter where the level ended up after a 25 minute DE session.

The I-J side drains on the I-J setup are more steeply sloped than the oil pan itself. This helps get the liquid back to the sump.

My analysis shows that when running with the bottom of the engine "flat" compared to gravity, at WOT on my car the forward acceleration of the car is greater than the forward acceleration of the oil down the pan until I get into 5th gear. That is, until I shift into 5th on a straight the oil is piling up at the back of the pan. This is the #1 problem with the oiling system on 928s.

hacker-pschorr

Just playing devil's advocate here....

If this really was a big problem, wouldn't the high HP cars (supercharged / turbo / stroker etc..) with stock oiling systems be popping rod bearings or something oil related left and right?

That would also make turn 14 to turn 1 at Road America the #1 place to spin a rod bearing for a racer like Jean-Louis and Paul due to how steep / long that hill is and how much acceleration their cars produce while going up it.
In the 5+ years I've been running with JL on the track, he has yet to experience an oil related failure.

I'm not saying the design is perfect, just thinking out loud.

GlenL

I'm not keeping good track of them but how many big power cars are run on the track and don't have dry sumps or accusumps and more elaborate vapor catch systems? Showin' off with a burnout doesn't give much time to create foam and the bearing isn't fed the foam for very long.

I recall being black flagged at RA after #3 several times. By then the foam had really built and was just gushing through the PCV system. This was a few years back, mind you.

There are two parts to the problem. The first is the oil ejection issue where the windage cloud gets excessive and the oil foam is being blown out. On a stock PCV set-up this causes the well-known black cloud behind a hard-driven 928.

Then there's the second effect of getting foam or air sucked into the pickup. This happens on straights and hard corners. That's what causes rod bearing failures. And that's why every serious trackster has an accusump or drysump. Rod failure is also a gradual process. (or usually is unless MK builds the engine) It gets starved for a few seconds at a time and eventually wears the bearing into the copper.

Being semi-serious I'm running an I-J windage kit. I've also got two spare blocks in the stockpile and 20 rods and a dozen Euro S pistons.

heinrich

very interesting ... I had not considered this.

hacker-pschorr

JL and Paul both have accusumps,
Tim Murphy's cars do not. His 87 automatic has not seen much for track time, his 88 has. Part of the Murf kit is removing the oil vapor return line from the intake. He also has a custom air / oil separator on the 88.

I'm still a bit shocked after your failures an accusump hasn't been added to your car.

I’m not trying to compare street driving to track driving, but the topic here is simply forward acceleration. There is the scenario of a car coming out a corner onto a long straight that might already be suffering pick-up issues, further amplified by forward G’s from the following straight.
That aside, some of these boosted / stroker cars are seeing incredible forward G’s well past a run of only ¼ mile. If the pickup under acceleration was that bad, by now at least one of them would have experienced an oil related failure. I’m going to go out on a limb here and say most boosted cars have the breather setup modified to at least pull the line off the intake, which has nothing to do with oil sloshing to the back of the pan.

It has been documented by a couple of people showing a drop in oil pressure on track 928 in left hand corners. I have yet to hear or see any data showing a similar drop under acceleration, even on cars with stock sumps / breathers.

I am not poo-pooing your data, just trying to learn since I’m obviously not grasping this very well.
Just for the sake of the argument, even the scenario of oil loss at the pickup due to forward G’s under acceleration can still be “solved” by an accusump.

The first modification I would do to any 928 is remove the oil breather line from the intake to a separate catch can / drain back. On an OB this is somewhat easy since you can simply tap into the stock oil fill tube.
IMO any track driven 928 must do this, no exceptions.


+1 which is why an accusump is going on both of my 928’s, and my replica Cobra.

Jean-Louis

Just to make it short, I have been running at Road America for 9 years now and the last four with a supercharger. But without my accusump and my own/developed vapor/oil recovery system I can guarantee you my car will not last two laps at RA. My accusump goes ON in the "carousel" every lap and my vapor/oil recovery system is pumping at least one quart of oil back to the engine every lap. Next event is PCA labor day race at Road America.

GlenL

My first engine failure was cracked rings. I had already added a separator before taking it apart and one is in there now. I figure the rings broke due to knocking and it knocked due to oil vapor lowering the octane. And with broken rings it really gushed the oil back into the intake.

After my 2 and 6 bearing failure I added a full windage setup. I was trying out a partial setup when it happened. I'm hoping, and anticipate, that will be a big improvement. Why no accusump? Good question. I'd prefer to go dry sump and can't figure out a good way to mount it for me. Full interior on the street car. Be sure I've spent hours looking into it. The windage system is quite cool and well done. The trap doors should keep the oil from sloshing back across the pan and the scrapers and screens will clear out the cloud.

Looking at the geometry of the pan a car would need to pull close to 1g of forward acceleration to uncover the pickup. A car that can pull 1g will have a 0 to 60 time of 2.7 seconds. Anyone that quick?

Foam or air gets sucked in when the sump empties over a long acceleration, and I'm not sure how long or if that alone actually happens, or when the oil available to the sump is reduced by it being other places. "Other places" includes in the heads, stuck on the pan floor and swirling with the crank. The last two problems build over time, especially foamed oil and windage. That's why, I think, quick blasts don't have problems. And also that it takes a lot of 1/4 mile runs to equal a weekend of DE or practice sessions. A typical DE weekend for me includes 4 hours of hard driving.


I've heard the "left hander" thing before but think left and right are equally damaging. JLP just posted about "The Carousel" at RA that's a long right-hander. The pan is fairly wide and that allows the oil to slosh away and it's easier to get sustained high g's in corners than in a straight line.

Yep. Or a fancy windage system with baffles and doors at the back of the sump. They don't seal it but beats the hell out of nothing. Or the "GTS" baffle.


Strong agreement here. It's so easy on a spider intake to run the line from the filler cap to a can and plug the line to the manifold. Anecdotes suggest those cars have a bigger ingestion problem.

Z

An old log from Tim Murphy's car:

[URL=http://g.imageshack.us/img443/tims1stgearacceleration.jpg/1/][/URL

GlenL

Thanks, Z. Figures Tim would be. Is that a 1st gear launch or what?

Anyways... My point is that it doesn't grenade right away when air or foam is sucked in. There's an oil film and it'll wear for a while before going ugly.