Dave928S

As it seems problem is essentially the oil won't drain down because it's fighting an upward stream of air in the same opening, maybe trying to get some separation of the upward air, and downward oil flows is the answer.

If tubes went down the oil drain openings to the crankcase main volume, from near the top of the valve covers ... is it possible the crankcase could be ventilated up those tubes, without carrying a heap of oil, to better allow oil to drain down around the tubes? I know the oil would still be battling upward air flow in the annulus space around the tubes, but maybe a path for air at higher revs/volume, free of any chance of an oil plug, might assist oil return and stop the burp.

This could be totally flawed thinking ... and maybe there's a good reason why this wouldn't work ... but it still seems that separating oil down from the heads and air up could be some of the answer, however that's achieved.

killav

Would adding a chamfer on the stock factory black plastic separators prolong oil ejection from the breather vents? Would it be better to point this chamfer away from the exaust cam? It seems that the angle cut onto the tube would provide more time before the oil could cover the entire tube and start forcing oil out of the breather.

Would adding an extra 1/2 quart of oil into the engine hurt anything? Running the oil level 1/2 quart higher seems like it could help the sump not run out of oil as fast, even if it was just seconds.

My recent run up to a higher velocity than I care to mention kept the engine at a high RPM for longer than I have ever done before. My PCV system is no longer stock, venting to the atmosphere due to the turbo modifications. Oil was blown out the two breather filters during that run. A lot of oil.

GregBBRD

Cutting the "extention" at an angle, to increase the time it takes before the "ejection occurs" isn't going to do much, if you have stock valve covers.
If you are venting both of the elbows on the passenger valve cover, one of those is connected to an "extention" down into the head. The other one has nothing. That would mean that you are completely filling the head with oil. Hard to imagine that there is much oil left in your oil pan, when that happened.

GregBBRD

Interesting thought. That might help, if the sheer volume of the oil isn't part of the problem and the issue is purely crankcase pressure, holding the oil in the head. If part of the problem is the volume of the oil, the vent tubes would only further restrict the oil return path.

slate blue

Maybe that is one of the reasons the 2 valvers don't have the same amount of trouble. That is because they are not vented in the cam boxes.

Dave928S

That's what I was wondering too Greg. It does seem to be asking for trouble by encouraging an airflow to blow the oil up ... which gets worse at high revs when it's critical that you have the maximum oil down low.

Dave928S

I think the problem is not so much differential pressure as such, but the increased velocity of air up the drains as a consequence of that pressure at high revs, reaching a point where it terminally inhibits the down flow of oil ... perhaps made worse by the natural increase in oil to the heads at those revs.

The tubes would mean less cross sectional area for oil drain back and so from that point of view might be counter productive, but perhaps there could still be sufficient cross sectional area for oil return considering it's not fighting the air to the same extent. I wonder what's different on our motors, and what head/cam box drains and vents are provided on other motors that don't have the problem we have?

I'm intrigued by this thread and I can't wait to hear how you finally improve, or hopefully solve the problem.

GregBBRD

I think that the 2 valve engines probably do the same thing...but the available volume of oil that can get packed into the head is much smaller. Think about what happens when it gets completely full. The incoming oil is essentially pushing the oil back down into the pan.

Why do I think this? Because the 944 Turbos (2 valve) loose #2 rod bearing, also. Probably a result of stuffing the cam area full and running low on oil in that sump. In the days that we worked on those engines, on a daily basis, we finally gave up and dry sumped the track engines. We designed a trick oil pump that had a drive on the back, to which we attached a power steering pump.

Dave928S

^^^^^
So are you thinking that oil delivery volume control to the heads is some of the answer?

928mac

Forgive me for not reading completely if I miss something but if oil volume is the issue? Can not a gal container be added at the cooler so that there is that much more in the system feed?
Just a thought
If the valve covers get full, could it be that windage impedes the flow down back to the pan?
The only fix I can see for that would be a line from the back of the head/cover to the front of the pan.

You guys that race will figure it out.

BTW, way dose this sweet looking engine (from a few post back) have distributors when CDI ignition is far superior?

hairywithit

runs just above the exhaust headers and appears to have runners into the block.
then runs around the front and ties into matching pipe from other side?
could this be a forced suction tied into the oil scavenge side of dry sump?

john gill

Tommorrow I will put the GT back in the dyno and measure the sump and rocker pressure and table the result at 6000 rpm .

Hilton

Good question - I was wondering what the pulley in place of the airpump location is.

A photo of the other side of the engine would be very handy - complete the picture of where all the shiny plumbing goes, and give some indication as to what that pulley powers.

jon928se

Previous posts point out that the volume of the crankcase remains the same, so any "pressurisation" is due to either blowby or is relative - ie oil is slung into the 1-4 head by the rotation of the crank thus "pressurisation" probably only occurs in the 1-4 head. Would seem to me that the ideal solution would be to prevent the oil from the crank being slung up into the 1-4 head in the first place but I can't figure how to do this so treating the symptom rather than the cause is the next step - Can the 1-4 Head not be vented to the 5-8 head drains ? With some form of crank scraper that ensures this return oil doesn't just get slung straight back to the 1-4 head.

john gill

THis cannot happen in my engine as it has the I and J crank scrapers system , the oil from the heads is diverted from away from the rotating assembly and down the sides of the block , the system very effectively shields the returns from the crank.

SO perhaps something else is happenning no point speculating until some measurement performed.