Jim bailey - 928 International

Because I can I have no idea how many hours and hours I have on the Streets of Willow there are no surprises unless a 911 spins in front of me which happens quite often as they try not to let an old faded very brown 928 catch them...

ew928

Jim B.,
Do you drive with the AM radio blaring and left arm leaning on the door armrest while operating the steering wheel spinner with right hand while at Willow Springs?

GlenL

Sounds like Ian is describing a Bernoulli effect. Formally the Bernoulli equation identifies that the total energy of a fluid flow remians constant. The sum includes kinetic energy (E.g., motion) and potential energy (E.g., pressure). This is the same analysis that identifies why a venturi creates lower pressure in the narrow passage. It's also Greg's (oddly put) "pressure builds from the back" idea. Pressure builds with loss of velocity.

Anyways, that'd be a clue as the starvation on the 2/6 journal. The oil is flowing past that passage first. If the velocity is high then pressure there is lower. People have suggested previously that there's a Bernoulli effect on that passage and that the mysterious ladder mod ("drill a hole?") addresses this.

A calculation shows that for the 52mm main journal the oil inside, at 6500 RPM, produces about 1.4bar pressure _out_ of the hole. So, if the effects stack up wrong a 2 bar pressure might be producing no pressure at the rod.

Jim: I'm running the I-J set, '84+ oil pump, an S4 pick-up and that Amsoil. Pressures are noticably better with nothing seen below 4bar above idle. I do keep my eyes on the road, though. And shifting at 6100...if there's not a corner within 200 feet.

john gill

this is a great thread

After recently rebuilding a late motor , I observed the narrow oil passages to the 2 journals closest to the oil pump , I wondered as this is one of the journals that seem to fail (2/6) what the effect would be to widen these 2 passages ,particularly in a track motor ??

JG

john gill

In addition to my previous observations I also wonder if at high volume , high revs this narrow passage could cause a venturi effect to oil passing by it , to the 2/6 journal , again interesting that this is the first item to suffer any problems !

John Veninger

Kevin Johnson wrote:
Yea, that's exactly what we all want

Stan.Shaw@Excell.Net

And to think I started this thread

Umm, I haven't read every post but my limited research has resulted in my belief that there are at least TWO causes of failure. Neither cause can be resolved by a single solution. Resolving one cause may prevent the problem under some or all of a particular use of a particular engine.

A known solution seems to be:
1. Drill the crank.
2. Drysump the motor.

Perhaps some people will run their motor in such a fashion that drilling the crank may not be necessary and others may find an accusump, scrapers, windage trays, etc. as adequate solutions.

Drilling the crank is a relatively inexpensive insurance plan... Just ask anyone who has gone through a few motors....

I plan to have two drysumps built for myself and Dave Cooley. The design will be based on JV's design. Thank you kindly JV

John Veninger

With a bit of picture taking from Mr. Anderson's car!

Cheburator

Erkka, this mistery modification to the block done in Germany does not work!

The TTT car, which had the "fix" on the block was for sale until recently with a 4.7ltr S2 replacement engine because the original 5.0ltr 32v with the "fix" suffered a 2-6 failure last year. I spoke to the vendor and he wanted EUR15k for a tired old car - the fact that it was a geniune Porsche Cup car mattered little to me...

Overall, from dealing with German 928 enthusiasts - there is very little understanding and willingness to "experiment" in the development of 928 race cars due to the prohibitively high prices for spare parts and massive field of 911s knocking about

atb

I think it depends Kevin, on whether we are talking Angus or Jerseys.
I was there when Louie made the "holey cam cover video", and based upon my eyewitness account, I'm thinking Jerseys.

Seriously though, it is definitely multifacted problem isn't it. Closing the barn door is a single action solution for the cow scenario, but I think what everyone is saying is that given the parameters of this oiling issue, there isn't a single component solution. If you could keep the oil unaerated, wouldn't the design of the cross drilled crank still cause failure at high revs?

mark kibort

This could be the reason that our motors have lasted so long with no oil mods and Amzoil. 5 engines, lots of racing, no bearing failures.

Mk

928SS

a DS will also pull some vacume in the crank = more HP

seems it's an old, tried & true soluiton that's even being implemented as std equipment on many newer HP OEM motors now, so I don't think it's a 928 specific issue. good thing - cause other OEMs have solved the problem for us, at least in principle. we still have to cobble together the solution for ourselves, but there are plenty of components laying around that should work just fine

cows? no need to meet the cow just to have a good hamburger

Stan.Shaw@Excell.Net

ok, then I guess my first motor failure with Amsoil was because I DID have an accusump. Cool, now we have a new source of the problems. If you have an active working accusump you may have a failure. Is that your point MK?

Stan.Shaw@Excell.Net

So what bearing failure do you think the drilled crank resolves if not the 2/6 where essentially all known bearing failures have occurred under race conditions.

Seems like you are now AGREEING that a drilled crank is a solution to some bearing failures, which is what I have been saying all along....

FlyingDog

If a cow tips in a barn and nobody is there to see it...Amsoil is a goat.