Lex_GTX

I am a little confused about the AOS vacuum connections and would like some clarification. Starting from the top of the AOS:

1. I understand the connection at the top is for pulling vacuum (especially under boost/high air velocity) and it connectors to the J-boot or turbo inlet pipe before the compressor.

2. What does the hose that comes from the side of the AOS connect to Is that connecting to the crankcase from where pressure is relieved?

3. What is the top o-ring connected to? Is this connected to the crankcase?

4. What is the bottom o-ring connected to? I assume this is where oil drains into the pan when filling. Again another crankcase connection?

Thom

2. goes to the engine mount to create vacuum at the turbo outlet to help pull the oil going through it. This type of vacuum line is necessary on any engine where the turbo oil return line ends below the oil level in the sump, which is the case on the 944T engine.

3. Yes

4. Yes

Lex_GTX

Thanks do you have a picture of number 2? And by turbo outlet you mean oil return line? There isn't much vacuum at idle for example in the j pipe (turbo inlet).

Lex_GTX

Also I can't find a vacuum diagram showing the AOS. Does anyone have one?

Is there a valve in the top of the AOS?

Scott H

Picture of the turbo vent (pardon the mess) Attachment 1365705

The later cars had a little valve in the hose coming out of the top to vent excess pressure when the recirc valve dumps pressure into the J-boot.

zerMATT951

Here are a few more AOS and turbo oil drain vent photos that may be helpful.

Lex_GTX

Thanks for all the posts and pictures. It appears it is a very simple crankcase ventilation system that goes to the turbo inlet. There is no vacuum in the AOS especially at low throttle so I am not so sure where idea about it pulling oil to drain the turbo comes from.

Another question - has anyone considered running a PCV valve to the intake manifold on this car? It might help with low load crankcase ventilation and oil consumption.

Thom

Check this thread. Should give you all the answers you need.

Lex_GTX

Thanks for the read. Didn't realize there would be so much vacuum pulled through the front of the turbo at low airflow rates. Also interesting to see that as pressure drop is reduced in front of the turbo smoke at idle starts to show up.

Generally you want as little pressure drop in front of the turbo as possible for performance in order to reduce the operating compressor ratio. The bigger the intake the better but this then seems to require a PCV system.

I am curious if those that ran a PCV valve they noticed a reduction in oil consumption at all due to the higher crankcase vacuum.

Jacob Turcotte

Does anyone know the part number of this hose? Or can anyone provide a link for where to purchase it? Thanks

Scott H

Pretty sure Porsche wants you to pay $Alot for a new one complete with the metal line, if they still even make them. Lindsey Racing sells the silicone replacement that's picture. https://www.lindseyracing.com/LR/Porsche/LRA-TDVH.html