924Board.org

[sparky001]

Hi all,
Not a mechanic, just a prospective engineer. Been researching about this and possible solutions/upgrades. 1979 924 turbo UK exported to NZ, so noticed the oil coming out of intake to find the Air Oil Separator (AOS), to be basically filled and was most likely caused by the aftermarket hydraulic line with a size reduction near the AOS return that probably allowed stuff to build up?

From a forum post there doesn't seem to be a direct upgrade due to the engine producing too much oil vapor? Hence the abnormally large vent hose (top right, #35 in diagram)
https://www.autoatlanta.com/porsche-parts/hardparts.php?dir=924-80-85&section=106-05
https://www.924board.org/viewtopic.php?t=43986&postdays=0&postorder=asc&start=45

Mentions Mann+Hammel Provent 200 but 150 is better? 100 vs 200L/min of blowby. Which seems a good option, unsure where to acquire one and they seem to cost quite a bit... Just uni budget things. Did find an AliExpress fake? But seems I can put genuine filter in it.
The other good one is the IAG one, its has amazing baffles and filter, but the big feature of allowing coolant to pass through a block attached to it. Basically stops water condensation in the can, although it already lives right next to the coolant expansion container which would warm it up enought to stop condensation already? Unsure....

If anyone knows about the 'average' production of blowbly (L/min) and if reducing the pipe to a smaller diameter to enter the seperator will be more harmful than beneficial, would be appreciated.
Don't really want to switch to a catch can due to the amount of oil vapor, unsure if that was from long term or short. Rather not let the engine starve of oil...

[924RACR]

The stock AOS should drain any liquid back into the pan by the bottom hose. If yours is full of oil, that drain hose (#22 in the parts diagram) would seem to be plugged or otherwise obstructed?

I've had at times quite substantial blowby on my motor, but never had the AOS fill up... the stock design is a very good one IMO.

I think a catch can is a very poor idea, agreed.
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[Cedric]

I happen to work with these types of systems every day, though significantly more advanced

How small is the hose? you can always replace it, shouldnt block very easily though, try to clean it out and see what comes out.

The original unit is great at handling fluid oil, but as any other similar units the mist blows through it (like most passenger car and after market units). Filter units are significant better in that regards. But for a completely standard engine you should be able to get it working with the original unit, by cleaning it out and try cleaning all the hoses. Be sure that the mesh in the crank case breather outlet on the engine block isnt clogged, any restriction will increase the crank case pressure and oil might not drain properly from the AoS.
_________________
1980 924 Turbo
www.instagram.com/garagecedric/

[sparky001]

Ah ok, yeah the return pipe was replaced with a 12.5mm hydraulic hose line with an open end fitting + a 22mm? hose that connects onto the AOS.

Look inside and can see it reduce harshly and have some minor corosion, where all the gunk was built up. Nothing for the rest 90% of the hose.
I talked to local workshop and said catch can pretty good, but he did say not 100% since hes got a new motor for racing.

Budget wise, I might just leave it alone and replace return. If its still pretty bad, when I pull the engine out later this year for other jobs, I might look into it more.

The Provent200 is a pretty good option with a proper filter, just cost of getting it and all the new hoses/fittings.
Will probs update what happens and if I change anything for future reference.
Found your inside Cedric on another forum post which helped quite a bit.
Thanks

[924RACR]

I ran a catch can for a number of years on my GSXR-powered sports racer/prototype... it was always a pain, as you'd have to check and empty the can... and that's on a racecar which is getting a high level of maintenance, not a street car you just want to be able to drive.

Eventually I redesigned the system to drain back into the oil tank (dry sump) just like on the 931... it's been maintenance free for many years now, and I love it.

So I would NEVER advise a catch can, if it can be avoided. Since the 931 comes with a far superior setup... of course it would be a bad idea. Like retrofitting carbs onto a CIS motor...
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype