Hi!

I'm wondering if someone can tell me (and if possible show a picture) where the side connnection on the air-oil separator (AOS) routes and what function it has?

As I understand from my searches it should somehow connect to the turbo oil return line, but where on it and how? Bought a car that had a non-stock turbo (with modified return line) where this line had been plugged. Looking to restore it.

Is the function to relieve crankcase pressure or to help with evacuating the oil from the turbo? Or something else?

Thank you!
//Niclas Eriksson

 

Wow, I just pulled this off tonight! Wish I could tell you more, but, here is a picture of the routing (the red line follows under it) and the PET parts description page, which calls it a "vent line"

 

You are correct on both counts! The original KKK turbo design requires a lot of oil to the center journals/bearings, and therefore needs a means of evacuating all of this oil back to the sump----the 930 and subsequent 911 turbos all use a form of mechanical oil scavenge pump to achieve this.

The 944 Turbo engine doesn't have an easy means of driving such a device, so Porsche engineers had to rely on the low pressure of the engine air intake to help draw the oil back into the sump.

This is why some people have had trouble with integrating more modern turbocharger designs (which require much less oil to lubricate the bearings) by simply restricting/blocking off what is already there. The breather system is exactly that, a system, and needs to be carefully modified to maintain vacuum (or at least not excessive pressure) in the crankcase.

This (lengthy) thread has a good discussion about the subject:

https://rennlist.com/forums/944-turb...-pressure.html

 

Thanks, some great information!

The problem on the car is that someone switched to a much larger turbo and simply rebuilt the turbo mount and the oil drain without any vent on it.

I think this might be the cause of insufficient crankcase venting and I'm considering how to resolve it.

Right now I'm thinking I will simply add a connection with a hose to a catch-can and then into the intake from one of the plugs on top of the cam cover. Anyone has any advise? Good or bad idea?