jpn

Is it possibe to just uplug the AOS hose from the intakemanifold side, plug a rubber cap on the intake manifold and transfer the AOS hose to an oil catch tank????

And probably just to make sure the crankcase can vent enough, I add a fitting on the top side of the oil filler tube (which is where the oil cap is) and route a hose to the intake manifold where the AOS hose was suppose to be...in effect the intake still sucks out the vented air of the crankcase...

Thoughts are appreciated.... especially from the ones who may have experienced such problems and found solutions...

emissions will not be an issue where I will use the car....

Macster

No. The AOS reqiures engine vacuum to work properly. The pressure difference causes the crankcase fumes to flow through the internal chamber of the AOS -- I cut one apart and the chambers is shaped like a nautilus shell with ever decreasing radius of the chamber -- where the heavier particles of oil in the fumes are slung out of the air flow and against the walls of the AOS. Once on the walls the oil flows down back into the engine. The crankcase fumes now free of the oil is then routed to the intake manifold and the engine where the fumes are burned.

Furthermore, the AOS helps to maintain proper pressure in the crankcase: The engine crankcase is intended to operate under low pressure to keep fumes at bay and to allow water and unburned gasoline to boil at a lower temperature and thus the oil to shed its accumulation of both of these fluids. The fluids if allowed to remain present will decrease the oil's viscosity and its ability to work properly under high temperature high load condiitons. This is not what these engines need.

A vacuum hose from the intake to the oil filler tube cap would subject the crankcase to too much vacuum. The oil filler tube could collapse or air could drawn past the rear main seal. Along with air would be dirt/dust which would ruin this seal in no time and possible wear the crank diameter the seal touched to the point the crank would be ruined.

The AOS has a valve that controls the amount of vacuum the engine crankcase sees. It is when this valve and its diaphram that controls it fails that results in the AOS acting up.

The stock AOS is pretty robust, but you must pay attention cause it can fail. Even a replacement can fail. My 02 Boxster is on its 3rd AOS, having had the factory one replaced at 80K miles, the replacement replaced at around 180K miles.

I seem to remember reading about an aftermarket AOS or perhaps one from the GT2 or GT3 engine or one from Porsche's racing parts department that is supposed to be more robust but it is quite pricey.

Sincerely,

Macster.

jpn

Thank you for your time and patience posting....I was told that some guys just vent the crankase to atmosphere thru an oil catch tank...oil will accumulate in the catch tank and will have to be drained once ina while...its was done cause the car had a supercharger installed...can AOS still work properly with a supercharger installed..there will be positive pressure already in the intake manifold...are there other options if car has boost...

redridge

Most of the case, the AOS will be under vacuum because it is inline with the intake.... (the throttle pulls air in the engine). The good thing about venting the crank case is that it will lower the intake temp.

Dharn55

There is a Motorsports version of the AOS that is supposed to be "better/more durable" but costs about $500. It may also require some mods to gt it in place.

Macster

Even a NA car can approach near atmospheric pressure in the intake under WOT conditions at low engine speed and at other times.

Besides, a supercharged engine not under boost all the time. When it is the AOS valve closes off so high pressure in the intake doesn't pressurize the crankcase.

Also, when under boost blowby increases so the pressure of the crankcase atmosphere goes up and this helps the fumes flow out of the crankcase to through the AOS. It is a pressure difference that matters in some respects.

There's a thread asking about supercharging a '99 996 and one post by someone who installs the kit (Evo kit IIRC) claims the stock AOS ok.

These engines are intended to have the crankcase run at something less than atmospheric pressure. This helps keep the build up of unburned gas and water in the oil down to reasonable levels.

They also need a good vapor recovery system cause the scavenge pumps aerate the heck out of the oil along with the crank whipping around at high speed slinging off bearing oil and oil sprayed onto the undersides of the pistons by the piston oil jets.

Supercharge the engine if you want, but leave the AOS alone, unless the maker/installer of the supercharger kit recommends something else. He has to stand behind the product and his installation of it, so if he recommends something else you have to assume he arrived at that recommendation through trial and error.

Sincerely,

Macster.

jrgordonsenior

Let me add that these crankcases need to be under vacumn to prevent oil foaming. The Motorsports AOS that Macster mentioned above is a larger, dual chamber A/O separator (P/N 996 107 926 00). It was originally developed for the Koni cars, and found to work on Caymans and Boxsters. It's pricey at around $600. (Doug it used to be $500), but every Koni car uses one...