Tom. M

the drain channels in the heads (from what i can see) are quite massive.

Is this a problem of too much oil in the heads not being able to get back down..or one of oil from the sump being forced up the "drain " channels making them not work as intended at high rpms (and also holding the oil in the heads up there)?

AO

Very interesting. Not what I was expecting at all.

Looking at the pics posted by Rob early in this thread shows that the vents are not tied into the oil filler plate (at least I can't see it). If the crankcase is getting pressurized relative to the head, the route for that pressure to escape is up through the drain passages and then out the 4 vent lines. This could keep the oil from flowing down. Exactly what Greg observed.

If the vents were tied in with the oil filler plate, that should allow for the pressure to equalize between the crankcase and the head, right? Thus the oil should be able to flow back down to the crankcase with less restriction. Am I off base here?

Random thoughts...

Here's a pic of my new breather connections. The black pipe is connected in front to the oil filler plate (which I posted a pic of earlier in this thread). Then it ties into the both the front and rear breather tube on the head, and finally goes to a Provent. The Provent has a line that allows any oil it collects to run back through the dipstick (there's a "Y" welded onto the dipstick).



Now that I think about it... why do we need the vents on the heads? If we can allow for crankcase venting through the oil filler plate, shouldn't that be enough? Also, if the heads are filling up with oil, by having the vents - it provides an outlet for the oil. If we were to cap them off, the oil would have nowhere to go but back down to the sump.

I don't think I'm totally off base, am I?

soupcan

A slug of oil is suspended in the oil fill hole and forcing the pressure up the head drain holes and pushing oil out cam cover vents, so another way of draining the oil out of the heads is needed and or a new crankcase pressure vent location is needed, correct?

Tom. M

I am thinking that the pressure within the crankcase should be equal to the pressure in the heads (it's all connected)...but like AO suggested..allowing a pathway for the pressure to escape up in the cam covers forces the flow to be "up" the oil drain channels...probably aerating and keeping the oil draining down..actually moving up the heads....and out the vents.

I've plumbed both my passenger cam cover vents..into the one hole in the oil filler neck (using a T)..and blocked off the one going back to the MAF boot. I vent directly out of the oil filler neck...so all pressure should exit there. Maybe a vacuum pump (variable speed) hooked to the exhaust of the Provent....at high rpm...it kicks on and pulls strong vacuum through the oil filler neck...?

just some random thoughts.

James Bailey

Now I am wondering how much oil can the 2 valve cam housing hold ???????

blown 87

Something tells me that a scavenge pump is going to be needed, and by then you are well on your way to a dry sump.

There are not many places to put a dry sump tank though, gonna be a problem for street driven cars, possibly in the "dead cat" area. (the space behind the front wheels)

AO

928er

what kind of oil check valve was used for the heads? stock 928 or the 944 one?

GregBBRD

The drain channels get progressively smaller, as they go through the block. One side makes a very "hard" 90 degree turn, before it gets to the pan area.

GregBBRD

Only if the crankcase pressure was less or equal to the pressure in the head...gravity can only do so much.

GregBBRD

Since oil is ejected very early in the dyno testing, from the oil filler plate, we think that it gets restricted before the heads.

GregBBRD

Stock 928. The engine is for a car with an automatic and is going to spend the majority of its life as a street driven daily driver. We were concerned about oil volume at idle, so we felt we needed to leave the higher volume check valve in place.

Higher in the rpm range, this is obviously a problem. As Jim Bailey pointed out, "The exhaust cam is more of a "paint roller" than a camshaft at higher rpms."

GregBBRD

Yes, seems like that is true.

GregBBRD

Not nearly as much. Note the lack of vents....I'd guess that the entire thing gets filled with oil and the pressure eventually returns the oil down the drain holes.

928er

so would a vacum pump pulling vacum from the lower block help? Do you think that the a dry sump suffer's the same problem? Since the 928 engine runs a higher oil pressure than alot of engines do you think that using the lower volume check valves in the heads as well as pulling vacum on the lower block would help? In looking at my block there were 3 bosses under the intake.. Two for knock sensors and one additional that is plugged.... makes me wonder if I should add a vacum pump on all 3 ports since I'm not using them when I switch over to the ITB setup... I will have more room under the intake....