Black Arrow

I removed the AOS today to install fresh seals. Then I found a hole that wasnt plugged, or got anything that was supposed to put in there.. Whats the issue with this hole? Its the one to the right of the bigger AOS hole.


Heres where some people advice to drill a larger hole in the AOS right? To what size? And is there a opertunity to open up the AOS bottle, or is it totaly closed?


Is there anything more I should think about changing around the AOS while I`m down there?


Thanx!

Charlotte944

I just took a look at my '87 NA (Can't see this area on the 951), and the '87 has this same hole with nothing in it. At first I thought this might be for the diagnostic TDC sensor, but that is mounted near the speed and reference sensors.

As for drilling the AOS, I can see no reason to. The AOS is plumbed to the intake boot to scavenge combustion gas blow by and to maintain a partial vacuum in the crank case. The size of the hole in the top of the AOS is as an orfice. As with any orfice the differential pressure across the orfice and the flow rate through the orfice are a function of the diameter of the orfice. By increasing the orfice diameter you increase the flow rate (not a good thing) and reduce the differential pressure across the orfice (also not a good thing). I would think that a drilled orfice would cause more oil to be drawn into the intake.

Ahmet

Well, if you're running more boost than stock, or if your blowby is higher than what the factory accounted for, would you not want more flow across that orfice? The pressure difference may be a bit less than if the hole had stayed small but total flow may (would in my opinion) increase. Depending on your point of view that may or may not be a good thing I suppose.
Ahmet

David Floyd

Only when installing a catch-can is when some drill out the AOS.

You can open up the AOS, I did and filled it with brass pot scrubbers, be very careful, the top can be brittle and break, there is an o-ring under the top that has been known to go bad.

I don't recall the block hole, I have my turbo off so I can take a look later today.

PorscheDoc

Check the condition of the rubber on That metal line with the 90 degree rubber hose fitting that attaches to the side of the OAS, replace that if the rubber elbow is hard and rotten. Also make sure your rear balance shaft cover isnt leaking, if it is, you can spread a little bit of RTV around the edges to keep it from leaking.

APKhaos

I'm with Thomas on this one. What the heck is that hole to the right of the AOS port shown in his top pic?

Two of us were working together to drop my engine, and both of us are mystified about that port, adn what goes in there. It was obviously sealed by something. Anyone know???

Black Arrow

Thanx for all the support!

And yes, I`m running more boost than stock, and I`m going to install the LR catch-can Thats why I`m wondering to drill that hole. To what size do we drill? And all the spoon that will come from the drilling, does it stay down in the AOS or do it go some where? How do I open it up David? Mine`s stuck..

David Floyd

Don't remember the size, but I drilled out to match the ID of the top.

The top has little tabs around the edge to pry off, be carefull if you do remove it !!!

Drill with the AOS upside down and vacuum the shavings out, do not leave shavings in the AOS.

Black Arrow

Do you recommend to remove it? To install a new o-ring etc.. What can happend if it goes bad? Oil leak?

David Floyd

With the stock setup, if the o-ring is bad it will cause a vacuum leak, if you are venting you Lindsey can to atmosphere it will cause no problem other than leak a little oil around the top.

I would say don't remove it, too easy to break.

Black Arrow

Okai. thanx for all the help! Preciate it

David Floyd

Just checked my block, have that same hole, no idea what it is, but must not cause any problems.

jimbo1111

I wouldn't worry about the hole on the right. I noticed that the hole on the left has a cracked off seat where the aos o ring seats. I'm wondering if that piece broke off and fell into the engine.