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patkeefe 11-07-2014 03:03 PM

930 OE Crankcase Vent System
Can anyone give me an idea of how the OE crankcase ventilation system was plumbed on a 930? I am trying to figure out a better system for my turbo SC, and was curious as to how the factory did it.


Speedy Squirrel 11-07-2014 05:42 PM

The crankcase vent on top of the case connects to an oil separator tank in the right rear of the engine compartment. Vapor is sucked into the engine between the air filter and the air meter, and liquid is drained back into the oil tank. The part number for the separator is 930 107 321 01.

patkeefe 11-07-2014 06:50 PM

Thanks. I wonder if they work OK?

jwasbury 11-07-2014 08:33 PM

I believe the oil separator was added later in the production years. My '79 for example doesn't have one. The breather cover connects to a hard pipe that runs across the top of the long block and ends near the oil tank. A flexible hose runs from the hard line and connects directly to the oil tank filler neck. A second hose also runs from the oil tank filler neck (mounted higher up than the one plumbed to the crankcase) to the airbox.

jwasbury 11-07-2014 08:35 PM fine and my car has seen a fair amount of track use over the last few years.

Speedy Squirrel 11-08-2014 04:51 AM

I think they work better than no separator. The idea of course is to separate the oil from the air, and just draw air into the engine. It does take up space in the back though...


Thanks. I wonder if they work OK?

patkeefe 11-08-2014 06:05 AM

I'm interested in running a slightly negative crankcase pressure. I have to measure the crankcase pressure as it is configured now.

TurboKraft 11-08-2014 12:15 PM

The factory AOS works very well. You'll have to add a port to your oil tank (or use a Turbo tank) for the oil return.
Negative crankcase pressure on a Turbo -- IMO don't think you'll achieve that with a factory oil pump, and not once under boost.

gavinc69 11-09-2014 10:19 AM

On my SC turbo I ran both the crankcase breather pipe and oil tank breather pipe to a separate oil/water separator tank I made with some baffles inside. I kept all the fittings 1" to try and help reduce any pressure.
The pipe from the crankcase runs upwards from the crankcase and enters the separator at the lowest point possible. That way any oil that does end up in the separator tank can run back down into the crankcase.
I didn't want a setup where I have to check and drain oil from the separator tank.
I then ran a pipe from the top of the separator tank where you would normally have a small air filter down to the rear and underneath of the car to vent.
The pipe I used is temporary at the moment, its see through so I could see what comes out. So far just clear water vapour by the looks of things.
So far so good, I've done about 600 miles on it. Its about the 3rd attempt at getting a setup that works.
I may redo it again in the future, same way just better if it seems to do the job.

gavinc69 11-09-2014 10:34 AM

The pipe from the top of the oil tank connects to the separator near the top but then I made an internal pipe to run it down to the bottom inside so the gas's have to go back up through the baffle material, hopefully oil condenses on the material and runs down and into the crankcase.
Thinking about it now I could of just put both oil tank and crankcase connections near the bottom, would of saved some messing about, DOH!

patkeefe 12-27-2017 06:11 AM

I am dragging this up from the archives...getting the EFI conversion set up in the car (I ran it on my test stand previously, and it worked OK, but that was a bare bones setup).

I want to plumb a pressure gauge into the breather line, just to see how much pressure gets built up in there. Anyone got an idea of the magnitude of pressure in there, so I have a starting point for the gauge? It is hard to find any quantification for this pressure on the internet. I do think Chris is right about not being able to run negative pressure.

My issue is I do not have a turbo oil tank, and my air intake is now essentially an air filter on the turbo inlet, so it is hard to introduce crankcase vapors back to the combustion chambers without an elaborate check valve system.

Speedy Squirrel 12-27-2017 07:54 PM

It is no more than + or - 15 Inches of H2O.

patkeefe 12-27-2017 08:28 PM

Thanks Mr Squirrel. I will try to measure it with a Magnahelic gauge.

boosted79 12-30-2017 05:58 AM

Why do you want to route crankcase vapors back to the intake? Just vent it thru a catch can. I used one of the plastic stock AOS cans. I did not tie the bottom oil drain back into the tank, I just drain it periodically, no big deal, hardly ever anything in there. No problems with it.

fredmeister 01-02-2018 01:09 PM

Running vapor back into the combustion chambers is a bad idea as it promotes detonation. just vent the catch can to atmosphere.

I also don't recommend running the waste oil back into the oil tank. just drain it once in a while and throw it away with your other oil change oil.

I bought a nice oil separator from an aircraft supplier, I think it was aircraft spruce? They are much better designed than the crap Morosso or JEGS sells. You want something that actually has internal baffles to slow the air velocity down and condense the vapors.


Speedy Squirrel 01-03-2018 04:42 AM

Fredmeister, I think you will find with further research that the detonation claim is not true. Oil burns so slowly that it has no effect on detonation in gasoline engines, even highly boosted ones.

flightlead404 01-03-2018 06:41 AM

I've been running a catch can for 2 years and there's not enough in there to be able to drain it yet. If you're getting enough oil in that catch can that draining it is a maintenance burden something is wrong.

patkeefe 01-03-2018 09:47 AM

My interest here is actually to run a relative small negative pressure in the crankcase.. I would like to do that without utilizing a vacuum pump, which I feel conflicts with the oil pump's scavenging ability, adds a ridiculous amount of complexity and is just plain overkill. I had problems in the past with excessive crankcase pressures, possibly due to the fact that I was running stock 8.5:1 SC CIS pistons with a turbo. Now, I have JE pistons custom built for this application at 8.5:1. Crankcase pressure may no longer be an issue. But, I still want to be able to quantify the crankcase pressure relative to the atmosphere.

Maybe I could just run an old style draft tube like a 58 Chevy.

TurboKraft 01-03-2018 10:25 AM

Pat, we haven't seen excessive crankcase pressure issues on the 8.0, 8.5, and 9.0:1 Turbo engines we've built as long as the cylinders were good and round, and the rings were of proper tolerances and seated.
On a race-oriented engine set up a little more loose, we can get some blowby and resulting crankcase pressure. It can spit oil droplets out the breather hose. To address this, we typically use the factory AOS system, draining back to the tank per factory. There's seldom oil out of its breather port (the hose that ran back to the CIS air filter housing) so we route it high in the engine bay and then back to the air intake. If there's concern, it can be vented out underneath the car away from tires and the hot exhaust.

patkeefe 01-03-2018 06:21 PM

Thanks Chris,
As I mentioned, I had an issue in the past with the old engine configuration. I just want to prevent it from happening again. I may have to look into a third party AOS.

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