IcemanG17

If I can save only 1 928er from the same fate I suffered....that is a GOOD thing

Rod bearing inspection-replacement is a VERY good idea for track 928's...a nice bit of insurance vs a ventilated block, that I wasn't very far away from

entropy_engineering

Hey I can't remember if I stuck this up in another post already or not, but I always use transmission assembly lube I think many of the engine assembly lubes are too thin. Before I put the t-belt on spin up the oil pump with a right angle drill or the like and have someone say when the motor starts making pressure. Then when it's back together you won't have to wait for it to prime.

Oil pooling in big DOHC heads must be relavent to BMW too, as they used two small electric oil pumps on the M5 to return oil to the pan when cornering hard.

Daniel Dudley

This is what David Lloyd always said.

Kevin Johnson

No, Spec E30 racers, say, suck in aerated oil and this causes a pressure drop. Lots and lots of data there. I agree that many engines do uncover the pickup under various conditions but it is hardly universal.

mark kibort

look at the oil level pictures I simulated with water. you are not going to uncover the pickup with 1g of cornering force, nor braking force. the aeation, due to foaming oil would be a answer, or too much oil stuffed in the head, but Im thinking that problem might only exist for the open road racers that go 6000rpm for 30 mins straight.

dr bob

Mark--

Take a few quarts out of the sump, simulating the oil moved to the heads under higher loads. Now aerate the oil in the sump, with only the bottom 30% actually liquid; simulate that by taking 3 more quarts out of the sump. Now tilt the sump to a 45º angle to simulate 1G loading in cornering and/or braking. Is the pickup still covered?

mark kibort

why is the oil being aearated? 3 quarts missing and the oil level is way below the crank! way below . proof is that I still have 4-5 bar pressure at 1.4 gs over a 7 second duration, and 5000rpm.

I think if there is problems due to foaming its the oil, not the system, or I would have grenaded my engine 10 years ago and so would have scot.

Kevin Johnson

Try decreasing the density of the oil by figuring that the system is working with 18-27% aerated oil (free air percentage). So, roughly, you then have an increase of 18-27% in the volume of air/oil. Only the pressurized oil in the galleries will be condensed down to neat oil.

The oil pump in the 928 is oversize and now we know from careful examination of development pictures that it is over-driven. The pump also communicates internally and the relief circuit recycles output internally. These factors, among others, allow it to operate with an input of highly aerated oil, so removing three quarts of air/oil from the sump is dubious. Observation of Louie's video also makes a resultant claim of approximately four quarts of air/oil mix in the heads suspect -- this is about 4000cc by volume.

Kevin Johnson

Modern wetsump engines are designed to run well above the sump oil reservoir and yet the percentage of air in the oil increases with rpm. Foaming means many things. An oil with a good anti-foam for the surface may increase entrainment of small air bubbles.

mark kibort

I kind of get it.
by the way, when i take a oil level reading after a hard race, i dont see any bubbles on the dip stick. i wonder if that amsoil is just that good in fighting off the foam!

IcemanG17

Since "foaming" clearly is an issue......the early pan is designed to reduce it.....vs the later pan which isn't....

Glenn Evans

Not so complicated. The big ends pass only about a tenth of an inch above the surface of the oil when it's level with the full mark on the dipstick ... on the MY82 engine, anyway. The full mark on my MY80's disptick is about 0.2 in lower.


http://groups.yahoo.com/group/landsh...unt=20&dir=asc

Kevin Johnson

There is a temperature dependence of the Henry constant. Hot oil is less able to allow air to go into solution while passing through the pump, ergo there are more free air bubbles present. This causes the oil pressure to drop, ceteris paribus.

Translated: use an oil cooler.

Kevin Johnson

Many racers add a sight tube coming off the side of the sump; this would be a better indication. Also, it allows aeration levels to be monitored during dyno pulls. A small camera mounted to observe it and then synchronize those images with a data aquisition system on the track would be interesting. Multiple sight tubes arrayed around the sump with visual monitoring would be even cooler. It's just money, right?

dr bob

Multiple taps on the sump for sight glasses are also places where things can leak or get broken off.

To see oil foaming in the sump by way of a side-tapped sight glass is tough. Virtually impossble in a classic bottom tap, vented-top sight glass. You really want bulls-eye window glasses at various locations on the sump sides. They would let you view the actual conditions inside the sump.