Tony

:Late to the thread here, but perhaps a less intrusive way to drain the oil would be to modify one of the cam seals at the aft end of each head..the one were the cam does not extend into ?

Tony

Although i wont see 6000 RPM for those durations, it makes me want to rethink mine. Perhaps the CRANK CASE vent SHOULD NOT be connected to the other two vents on the valve covers. Valve covers would have there own vent...as would the crank shaft/block area...uh..to the atmosphere.

killav

The black plastic tube aka the oil separator (NLA part number 928 107 731 01) might work during normal driving but probably just gets submerged in oil at high RPM---at which point, acts like a reverse vacume cleaner blowing oil out everywhere. Especially under BOOST.

AO

Why even have a vents on the valve covers?

Just to enrich the discussion, here are a couple of diagrams for the stock setup (32V). S4/GT on the left and GTS on the right.

GregBBRD

My first thought was a vacuum pump... I even bought a really nice billet one and started figuring out how to mount it. I got stuck when I started trying to figure out how to deal with the huge volume of oil that would be mixed with the air. It's going to take a pretty big oil separator and then a method of returning the oil from the bottom. The separator will fill very quickly....

GregBBRD

There is plenty of room, in the heads, to effectively separate the oil from the air, if you vent the crankcase into them...The problem is that this just adds to the oil already trapped up there, once the drains are overwhelmed.

GregBBRD

Actually, the left is early GTS and the right is late GTS....

GregBBRD

Exaactly what happens on a stock vehicle. This is why the intake system gets "filled" with oil when the cars are driven aggrressively.

I'm not into the supercharger thing...so I have no idea what happens, under boost.

killav

My thinking was that X amount of boost translates into more blowby therefore more crankcase pressure to blow the oil out of the stock black plastic tube.

I wish there was a flat type oil separator built into the cam cover that could not possibly get submerged.

We are talking about two problems though. One of them makes a mess, the other fries the bearings.

928er

I think I'm going to replace my cam breather hoses with clear tubing to see what is happening on the dyno......

soupcan

I thought I had read here years ago that someone already did that....time to use the search button.

Tony

Proff. Ott has video. Not of the breather tubes but of what goes on under the cam cover.

hernanca

Timely thread!

I have been thinking of upgrading the breathing on the stroker (I bought the one Greg built for Brian Fleming), and have been reading up on breathing options for these motors. Based on what I have learned, I have not liked the idea of allowing any significant flow out of the heads. It just seems to encourage an undesired exit route for the crankcase pressurized "fog", because, for DOHC motors anyway, it would compete with a more significant amount of oil wanting to drain back from the DOHC heads (as opposed to pushrod engines, needing less oil in their heads, and which have those cool breathers on their valve covers).

I'm not a Physics major, nor have Greg's practical experience in this, so I could be pretty far off here.. but plumbing exit routes from the heads to the intake plenum, as I have heard that many folks do or want to do, would just seem to make the problem worse at higher RPM's by providing an even lower pressure, and thus more appealing, exit route, for the pressurized fog. I don't know to what degree, but at the higher RPM's, this would seem to have the same effect as increasing the diameter of that tubing, even if they have restrictors, and there are many more of these tubes coming from the heads than from the crankcase.

Greg, I suspect it is safe to assume that you've done the calculations comparing the total area of the stock openings (crankcase, heads) vs. this set up. To me, just going by the pictures, the stock crankcase vent plate plumbing looks more restrictive than stock, but you also have that custom oil filler (right rear corner) which may provide additional venting to the crankcase.

For the crankcase only, does the total area (of exit openings) of the current set up, exceed the stock set up? My guess would be that it should do so by about 30%.

For my street-only 86.5 based stroker, I am coming up with the following set up:
928 International oil deflector plate in oil filler location
928 Specialists SharkVent system, customized as follows:
* ProVent inlet connected only to the oil filler with Big A&& Hose
* Depending on pressure/vacuum readings: either two one-way (inlet only) filtered breathers on both heads, plumbed to the fenderwells; or just plug the head outlets.
* draft tube connected to ProVent air outlet
* drainable catch can between ProVent outlet and drain back to crankcase (catch can overflow, if any, would drain to crankcase)

Ketchmi

A long time ago I built some air/oil separators that go in the cam covers and installed small K&N filters on the top. I then ran a vacuum from the inlet of the air pump (using a venturi) through another air/oil separator (which drains back into the pan) to the oil fill. This system when properly adjusted pulls air from the crankcase (and oil down the cylinder head drains) using the cam covers as the air inlet. When it's not properly adjusted, it will suck the oil right out of the engine, through the air pump and inject it into the cats. Good for killing mosquitos but not for anything else. Granted, this car is supercharged and with over 600rwhp, doesn't see extended WOT for any extended amount of time but the K&N filters are still pink after several years of use. Very little vapor and no liquid oil comes out of the cam covers.

BTW, I use stainless pot scrubbers in my air/oil separators...any good reason to use copper other than being able to corrode with condensation?

andy-gts

wouldn't scavenging the crankcase to a negative 8 or 10 psi potentially solve both problems and then dump the suctioned oil vapor from the crankcase into a separator or catch can and this will encourage (through pressure differential) to empty the heads down the respective drainage pathways. All the time giving you the extra 15 hp the dry sump guys from doing this?