I guess that would be a good indication that oil packing into the heads from the circuit was not the source of the 2/6 rod bearing failures.

 

In theory, yes the pump will work without much oil going through it. Time will tell.

I have heard, recently, that the newer Chevy engines do "pack" oil into the heads, also. I have no idea. I know a lot about very little.

 

So, I guess you are saying that now you do not want a free system to test. No problem.

Once again, from five years ago, to refresh your memory:

The stock Porsche 928 V8 wet-sumped engine, both 16V and 32V versions, has two very well known problems at rpms above ~6300 rpm: 1) oil aeration which is definitely fatal to the engine; 2) oil ejection. Many, many attempts have been made by the factory and aftermarket to correct these problems in the 30 plus year history of this engine.

With regards to the fatal problem of oil aeration, the Ishihara-Johnson 928 windage control system allowed the Dutch Stallion team to run their wet-sumped 928 S4 engine at typical rpms of 6800 for the first half of the 43 hour 2006 season (not including practice) and 7200 for the second half with stable oil pressure. This was accompanied by a 10 degree Celsius drop in coolant temperature from the previous years engine which had less power. This years engine is NA and develops 420 rwhp.

To our knowledge safely running this sustained rpm level in the wetsump engine is unprecedented in the history of this engine*.

Prior to the installation of the windage control system when they attempted to run their engine at 6800 rpm it failed in two days.

Upon teardown of the engine at the close of the season no discernable damage had occurred in the engine.


~~~~~~~~~~
Testing trumps theory, right?

And then:

To be very clear, the windage control system does not and cannot correct the second problem of oil ejection. In some situations it may even make it worse.

Louie Ott, in a Rennlist post suggests:

The oil filler breather I made can be seen on my web site on this page.
http://www.performance928.com/cgi-b...ass_parent=1128
Scroll down to the bottom and there are a couple of pics. I have some basic drawings (no dimensions) which I could email if you want. The inside of the aluminum cap has the threaded part from the old cap. Turn down the outside of the old cap. Turn out inside of the new cap to fit outside of old cap. Epoxy old cap inside the new cap. A hole has to be bored in the old cap to fit over the swivel projection in the center of the new cap. The size of the copper pipe "street L" that goes into the center of the cap is 3/4" and is about the smallest size I'd consider using. If there is a way to use 1" size, use that. It might fit. This was just an experimental thing and it worked out ok. You need to vent a large volume of blowby, but don't want high velocity which would carry oil with it. That's why the largest diameter you can use is best. I don't know what others have made. One key thing is to have the inlet on the underside of the cap project down into the filler so any oil that is on the surface has a hard time turning the corner and going up and out the breather.

Rob van Kol has used Louie Ott's suggestion and added a baffle trap as well. The oil ejection rate for the Dutch Stallion Team car is now at .25 liters per 50 minutes racing. These suggestions really work.



* To our knowledge safely running this sustained rpm level in the wetsump engine is unprecedented in the history of this engine. ...

In the mid 1990s, Porsche helped Max Moritz Racing compete as a semi-works team with the 928 GTR. Near the end of the season the hand selected engine provided by Porsche suffered the dreaded bearing failure.

See also the Kibort Effect for long term survival of the stock engines at lower sustained racing rpms.

During the development of the 928 engine there were strength problems with the original bedplate design. This bedplate design did have better windage control characteristics. These elements were largely sacrificed in favor of strength. It can be seen that Porsche was dealing with crankcase flow issues that later entangled Ford in the Modular V8 for many years. The oil pump was progressively driven faster and faster to compensate for aeration issues in this early development time and even a deaerater design element was incorporated into the large sickel pump. Unfortunately, the original oil sump design was also subsequently altered in the production engine after previously undergoing all this development, including a 3000 hour durability dyno test at full load and multiple 600 hour runs. See the chronicle entitled "Project 928."

 

I believe those valves were designed to limit pressure, not volume....

If they wanted to limit the volume, it would have been way simpler to just put in a restictor...not those elaborate valves.

I'd guess that at operating temperatures, the volume delivered to the heads will be very similar to the original pieces.

This, combined with the obvious tensioner problems on the 944S engines, is why I didn't bother with these valves.

 

Not at all, I'd love to test your product, in an actual dyno test, for you.

Obviously, you have not done this, for a 928 engine.

I just don't want to debate the reality of my testing. That would be silly.

 

I see references online that list the peak horsepower of an S4 at 6000 rpms. Typical durability testing for OEMs is hundreds of hours on the dyno sweeping back and forth between peak hp and torque. The designs of the sump elements indicates that a large amount of aeration takes place. Greg is not measuring the bulk density of the "oil packing into the heads" nor the bulk density of the oil in the sump. That is very difficult to do accurately. Mercedes used radioactive isotopes in the 1970s. Porsche styled their sump design after Mercedes but the slope of the rear of the pan is much less in the Porsche engine.

What was the percentage of aeration in your oil? A windage system affects the equilibrium levels.


I am sorry but he needs to do more research on existing research. Other people and companies have spent far greater amounts of time and money to scientifically study these problems.

 

The missing data here is how much oil flows through the system after the pressure relief valve in the pump kicks in. With most pumps the volume stays fairly constant -- gradual rise with increasing rpm.

 

I will need the stroke and outer swept diameter of the counterweights.

 

great discourse...... honestly we are lucky that people like Doc, Kevin and John continue to test and improve the inherently flawed 928 oiling system....

I am proud to continue testing the on track limits of a slightly modified 928 oiling system....so far it has proven reliable...but I am sure changing only a few variables would drastically change my results... I am sure the low RPM powerband of the USA 4.7L helps keep the engine alive...while my engine spends significant time on track, most of it is fairly low in the RPM range due to the tall gears of the automatic and powerband that falls off a cliff after 5500rpm...

If I were building another 928 race engine, one that made power well past 6000rpm...which is quite easy to make happen....I will drysump it.... with stages that scavenge the heads... there still is lots of uncharted territory in 928 engine building....a big displacement engine that CAN spin to big RPM....do the math on that....crazy power...Mike Simard gave us a small taste of what can be done....with a streetable cam and low compression.... Imagine a true 454 at 13+CR with a lumpy cam running race gas.....700+ whp with ease.....not to mention BOOST

 

There isn't any major form of racing that doesn't use dry sumps that I'm aware of. After the oil has done its job- pumping up the lifters, lubing the cams & cooling the springs, it just makes sense to get it out of there. Greg has done a great job & it's a very neat installation. It's amazing how he can fix things the factory could not or chose not to.

 

Fairly recently there was an opportunity to watch this sort of engineering/accounting/? debate go on in an OEM. First, though, Mercedes does present dry sump aeration data in that 1975 SAE paper alongside the wetsump data. Perhaps to say to Porsche that if you really exceed the parameters of these tests then take this path. I do not think Porsche had the money to redo everything; many people here have the experience of trying to figure out where to locate dry sump components for a 928 street car. Even now, Porsche chooses to try to integrate the dry sump style system within the area of the engine itself.

The Modular V8 in the Ford GT was dry-sumped and used a full windage tray system. More importantly, the block was re-engineered with respect to the head drains and breathing/pumping of windage and blowby gases. So they already had this solution in hand. When the Coyote 5.0 was developed they passed over using the now-already-available dry sump and instead continued playing with the existing passages (and adding new ones) -- again with a full windage tray. The Coyote motor is more advanced technologically and you could certainly choose to add a dry sump to it. Something to think about.

 

Hello ALl

THis has popped up on the 944 board , will these Clevite high performance Nascar rod bearings CB-1628HX fit the 928 ?

I was not aware that the 944 968 shared a similar size bearing to the 928 ?

 

Yes, 944 and 928 share the same rod bearings with the 928 engine.

That Clevite bearing is significantly narrower than the stock rod bearings. Not exactly sure what that is going to do...I've been thinking about that, since I saw that post on the 944 board.

A "Chevy" rod uses a much narrower rod bearing, but the rod is also not as wide. That narrower bearing is limited on how far it can rock, by the thrust surfaces touching the crank, or the other rod, in this application.

Seems like the narrow bearing, inside a wide rod could allow more "rocking" motion and thus accelerated wear on the edges of the bearing. I'm thinking of it as a "leverage" type of issue.

Keep in mind that a 944 piston is perfectly centered over the connecting rod and the rod beam is perfectly centered over the crank throw....this is easy to do, on a 4 cylinder engine.

In the 928 application, the rod has a "built-in offset" to accomidate the fact that the rod journal on the crank isn't centered under either of the two cylinders it serves. This is obviously going to "make" the rod try to "rock" on the rod bearing, every time the piston is pushed down.

However, I'm not sure if this is a significant issue. Might not be a problem, at all.

I thought that I'd run this past my friends at Carrillo and see what they think, next time I talk with them.

 

Thanks Greg

I wonder how much clearance between the bearings in the journal , in a stock 928 crank ?

I am about to dissasemble and check this in a stock block , nice to have options though ?

 

.002"-.003".

I ordered one of those Clevite rod bearings to be able to look at them closer and see how they actually fit.

You know that I'm remaking 5.0 and 5.4 cranks with "smaller", narrower rod journals, less weight, and properly drilled for use in high rpm stock stroke engines? Should have the "first" cranks here, in about 3 weeks....but I've heard 3 weeks for the past 3 weeks. I have the rods already here, to fit these cranks.

This will be very trick stuff, for anyone that is using one of these engines in other than street applications, wants a "mini" stroker, or has a stock GTS with the "weak rods" and a 62 pound crank.