ptuomov

> Here's something I've learned by searching the forums: For their cup-car
> prototype, Porsche installed the 944-2 oil pressure relief valve to the cylinder
> head. See http://www.norcal928.org/928cup/928CupSpecs.pdf. The part
> number is 944.107.139.00, or 42 in the picture in the link:
> http://dcauto.gotdns.com/illustration/index/438291925. Anybody with any
> theories what this accomplishes?

So we did they do it?

rockcrete

I just read that link, it's all about exactly what I was saying - keeping oil down around the pickup! It even goes so far as to actually say so.

It would be nice to actually see the movie it refers to that's about the oil pan modifications!

Louie928

I would suppose they used the pressure regulator because they thought normal oil pressure put too much oil up in the heads. At high RPMs, in a corner and especially a left corner, there is too much oil in the heads. It's aerated foamy oil not normal liquid oil. It comes from the crankcase and is pumped up the drainback passages. The foamy oil doesn't drain back very quickly even after the corner is over. Eventually, the pickup becomes uncovered, but even before that the oil the pump is picking up is full of air and looks like it's been in a blender. The foamy oil is thrown/pumped up to the head because the sump doesn't have adequate control to keep oil from sloshing out and up the side in a turn. The oil in the sump is way too close to the spinning crank and the sloshing oil gets thrown to the right side of the crankcase by the rotation of the crank. It also gets trapped in a spinning ball of oil rotating with the crank. I've read that it is common to have 1 or 2 qts of oil trapped in the spinning crank. Soon there isn't enough oil left to keep the oil pump pickup covered. The 928 crankcase breather is extremely undersized and doesn't vent enough blowby pressure at high RPM and load. Excess pressure in the crankcase escapes up through the oil drainback passages to the cylinder head where it vents out through the cam cover vents. The blowby escaping up the drainback passages carries the foamy oil up into the head where it stays for a while.

hacker-pschorr

FWIW I own one of the 16V 944's that most likely has that pressure regulator installed from the factory.

Mine ate up a rod bearing without any track use.

blown 87

Some folks do some rather "spirited" driving on the public roads.

RKD in OKC

I hate to say this,

So... according to Louie's description a low foaming oil like Amsoil may well be a good preventative measure.

Arrrrgh.

Z

The very first person that I ever heard mention using the 944 valve to restrict oil going to the heads in a 928 ended up blowing the 2/6 rod bearings in his car.

Alan

Wouldn't that make it just a 2 rod bearing though... (is it in fact the same cylinder as the most common crank/rod bearing failure mode on a 944? - assume the crank oiling is similar)

Alan

Louie928

That and Mark's disciplined procedure of no high RPMs in corners. I think Mark's good luck isn't all luck. Redline is good oil too. I use both. Amsoil pours "thinner" at room temp than Redline. Both 20W-50. Maybe Redline has fewer viscosity modifiers. Hot oil pressure is good with Amsoil. I've heard that fleet oil, and diesel oil for the non foaming properties and higher zinc is good too although I have no direct experience. Delo from Standard Oil and Shell makes some too, Rotella I think.

Z

On the 944/951 it's the #2 bearing, on the 928 it's the 2/6 bearings. Those are apparently the most common ones to go, but other cylinder's bearings have also been the ones to fail from what some 928 owners have told me that they experienced over the years.

rockcrete

How is restricting the oil to the head even remotely related to losing a rod bearing???

2/6 have already been labelled as detonation prone.

Detonation hammers the crap out of your bearings - even if they have oil.

There is no one magic cure for these problems, it is an oil system, and as such, you must take a system approach to it.

BC

Redline non-race oil has quite a bit of a detergent package from my experience. I like it alot.

RKD in OKC

I can understand keeping the rpms down. I've found my autocross laps are faster if I short shift and keep the revs down below 5500. Maybe that's just the x-pipe talkin.

GlenL

Anyone tried a ZDDF additive?

http://www.pegasusautoracing.com/pro...p?Product=1678

Ain't going to hurt, I figure.

mark kibort

This year, amsoil has traded a lot of the detergents with more zinc with its 15-50 racing oil. i guess if you are changing the oil as often as I do, its probably a good trade off. (every 3 races, the oil gets changesd)