You can reroute the AOS vent line to the air filter box. No more excessieve vacuum (at zero throttle or idle) applied to the AOS diaphragm. The AOS will stay always in open position and never fail. In fact in theory this is also how it is done on the gt3 models. There the vent line is not subjected to huge intake vacuum as in the NA m96/97 engines.

No more greasy throttle body, no more oil and gunk in your intake. Only drawback is the air filter gets dirty a bit more at the spot where you let the rerouted line enter the air filter box. Further advantage is a colder air intake temperature as hotter AOS fumes are rerouted and have more time to cool down. Makes for some extra noticeable bhp. Engine runs smoother at idle as no unmetered air gets into the engine.

As said before the main advantage is no more oil in your intake. In case of an internal problem which causes the AOS lines flooding with oil and the positive crankcase pressure pushing the oil out, it ends up in the filter box rather then the intake to possibly cause a hydrolock.

You could put an additional catch-tank to filter out any oil getting past the AOS. Saves you some cleaning of the air filter box every time you change the air filter.

I have this set up and it saved my engine half a year ago when my head 1 scavenging pump gradually lost its pumping capacity. At some point the AOS spitted out oil every right hand turn I made. In the beginning just a tiny bit. But got worse and worse and the car started smoking of the oil ending up in the air box and starting to drip on the hot exhaust, I did not have an additional catch tank at that time. At some point I connected a small bottle to the line and only one right hand curve at moderate 35mph resulted in 200ml of oil in the bottle. Imagine that going into the intake. Hydrolock festival

It turned out the scavenging pump in head 1 was not able to pump the oil back fast enough and the AOS vent line in bank one got flooded with oil which found its way out via the AOS due to the overpressure in the crankcase.

To prevent the engine from this overpressured cranckcase scenario. There is now a second connection from the oil cap to the additional catch tank. So any overpressure in the cranckcase when the AOS gets flooded can escape via there.

if you analyze the setup of the 997.2 and it’s oil filler tube you will see it is exactly the same what Porsche has implemented in its later models. As well as the rerouting of the AOS line to a ‘lower vacuum at zero throttle’-position on the intake. It makes sense, not reinventing the wheel again.

I’ve read something about long term fuel trim being an issue with a catch can on these cars. Something to look into.

Here it is

http://986forum.com/forums/boxster-g...ket-aos-4.html

The AOS under driving circumstances (diaphragm open) is in fact a catch can, so I fail to see the influence on it during normal operation. Adding an additional open flow catch tank just helps to catch and condensate any oil dispersed in the crankcase fumes which gets past the AOS under extreme driving circumstances.

Remember with the setup as explained above you completely take away the excessive vacuum created by a closed throttle body in combination with high rpm. The diaphragm is always open as it should be ideally and it will never fail. Unless there is another problem within the AOS you do not need to replace it.

I understand the probability that in the U.S. you might not pass vehicle inspection. In theory it should be okay as the air is recirculatid to the intake only via an alternative route.

Did you read the thread in the link I posted?

I was thinking of integrating a removable catch can design to the OEM part. Stefan mentions that the bellows deteriorate due to exposure to acidic oil. I think adding a removable catch can to the existing separator chamber via a one-way vacuum shut-off valve will ensure that the AOS is always under the intended design condition, but will simply drain off the collected oil after each drive when there is no vacuum in the separator chamber. As the AOS works under intended design use, the operation conditions do not change at all, and hence there is no need to worry about the fuel trim. The device will keep functioning as stock, but gives the flexibility of draining out the oil after use. Draining the oil will ensure there is no change to flow characteristics inside the chamber, or oil churning up to turn acidic. Good oil maintenance practice, which is generally expected, will ensure that the bellows are not exposed to acidic oil. The one-way valve will also ensure that the oil from the additional catch is not sucked back in.

I certainly have not had a lot of time with the vehicle, and I have not spent enough time understanding the situation. But let me know what you guys think about it.