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All you need is a hose. Disconnect the AOS line from the plenum and reroute it around through the engine compartment to the air filter box under the air filter. During driving it will get enough suction from the air box in addition to the positive crank case pressure under driving to breath the crankcase fumes.
The extra catch tank is not necessary. It is just a neat solution to not dirty the air filter box too much or catch some oil if you have another internal engine problem which pushes oil out through the AOS. The connection on the oil cap is also in case such scenario happens and is there to let any overpressure escape.
Even Porsche understood this and implemented it on its later models. As you can see above the oil filler neck has a connection to the AOS (the big ribboned tube with the 90degr connection ont the oil filler neck)
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.
Has this ever been long term tested on a 996 to see if the theory works in the real world?
I have it 45.000 miles on my car. Saved my engine from massive hydrolock when my head 1 scavenge pump deteriorated and flooded the AOS. So in that respect it works. My indie who developed it has installed it on more then 250 cars by now.
I have it 45.000 miles on my car. Saved my engine from massive hydrolock when my head 1 scavenge pump deteriorated and flooded the AOS. So in that respect it works. My indie who developed it has installed it on more then 250 cars by now.
I have it 45.000 miles on my car. Saved my engine from massive hydrolock when my head 1 scavenge pump deteriorated and flooded the AOS. So in that respect it works. My indie who developed it has installed it on more then 250 cars by now.
Would he do an instructional write up with detail/pictures for us DYI Yanks?
I hope I'm understanding this correctly since I need to get my AOS replaced, could I do this instead with no downside ? Seems like it would be cheaper and a better option.
The air box idea sounds great. I think a non vented, inline oil catch would still be needed. Depending on how much oil people are getting, they may start fouling MAF sensors.
Would assume that the AOS developed for the 986 engine referred to in an above link was a fail? He made 10 units. His last post on that thread was 11/16. Seems like the fuel trim issue was insurmountable? Sounds like Silk's method to reroute the vent to air box is a good idea.
01-18-2019, 04:37 AM
