Increasing oil capacity of AOS to help with avoiding smoke screens - 986 Forum - The Community for Porsche Boxster & Cayman Owners

There are 3 basic versions of the AOS that I know of. The basic version that comes with our cars, and then 2 larger versions that some folks call the "Motorsports" versions - one is for 911 cars and one is for 987 Boxsters and Caymans, that I think can be retrofitted onto 03-04 986 Boxsters. Post #7 here has some pictures: Oil Separator Modification - Pics - AOS Motorsport VOS The reason I understand these bigger AOS won't fit on earlier 986 Boxsters is because the outlet of the AOS and the inlet on the engine is larger starting in 2003. But what if you were to open up a hole in the side of the oil chamber in the smaller AOS, and either epoxy/bond/plastic weld on a bump-out or an extension or a tube leading leasing to a reservoir with extra capacity, so that the oil chamber would have more time before it got full and then oil gets sucked into the intake? Maybe a 3d printed bump-out could be made that would make the original AOS oil chamber a little bigger? I could be way off, I have never seen the inside of an AOS, but it seems if the oil chamber could be made bigger it might help avoid some smoke bombs. I guess the other solution I have seen is to put a catch can in between the AOS and the intake, but what I have heard from folks that have done this is the following: 1. Add catch can between AOS and intake 2. Fill oil up to top line on gauge 3. Drive on track 4. Catch can immediately fills up with around 1/2 to 3/4 quart of oil and oil gauge reads down to about halfway between the marks, at which point no more oil goes to the catch can. I guess at least it didn't get sucked through the intake. I run my oil about halfway between the top and bottom line on the gauge and have no smoke bombs since doing so. I may start a new thread on this, but: * Has anybody ever done any mod to the AOS to increase the oil capacity so it has more time to drain back into the engine? * Does this sound like a terrible idea? * An unnecessary idea? Thanks Steve

I like your ideas.Certainly the AOS a part that needs improvement. I am not convinced that physical capacity is the biggest problem. The internal part that fails and causes the smoking is a small 'rubber' diaphragm. Replacing this diaphragm with a piece of Viton would probably make it last forever? Easier said than done ! There is another situation that causes the smoking -violent turns with very sticky tires.The oil just 'sloshes' up and overwhelms the system. A deep sump+horizontal baffle should help that problem. I plan to try the Viton idea if I can get a failed AOS to experiment with.

Quotes source post: 471576

I'm sure there are plenty of folks on this forum with a failed AOS to could donate to the cause.

cool idea. i'd thought about putting the catch can between the aos and the engine, but there are multiple inputs to the aos so would be a nightmare. if you were going to go to such extremes then go to an aftermarket aos altogether (lots out there for subis): Air/Oil Separator - WRX/STi/LGT/FXT - GrimmSpeed getting at the actual aos might be a good way to do it. here's a link to a thread with pics of one cut open: AOS DIY 997.1 C2 - Rennlist Discussion Forums should be possible to tap the chamber somehow. or perhaps remove the top diaphragm altogether, tap the opening and somehow route to an aftermarket aos? or ... why dump it into the intake at all? intake is just used for: vacuum, emissions (so the vapour doesn't go to atmosphere) and a place for the oil to go so that you don't grease up the road. so how about an electric vacuum pump? this would provide consistent vacuum, and it could vent into a catch can. I had looked into this; there is some talk online about using a secondary air injection pump. I think the issue is duty cycle - it would have to run 100% of the time, and pump oil and not just air. and the final note is that the boxster aos has gone through several iterations (check the last digit on the part number) - make sure you get the latest one for your car.

Below is a picture from that thread. [I believe that..] When the AOS separates the oil from the air, the oil goes into the big chamber at the bottom and then drains back into the engine. When the oil comes in too fast and completely fills this chamber, that is when I believe that the oil gets sucked into the intake. If this chamber was bigger (like on the "motorsports" AOS) you would be able to have more time before it filled. If it mostly overfills during high G corners, then having this extra capacity may be enough to keep from blowing a smoke bomb, similar to how the bigger Motorsports AOS does. This is my theory on enlarging the chamber with a 3D printed bump-out. Or two tubes that lead to an external reservoir that is at the same level as the AOS so it could gravity feed down and back into the AOS. Ben006 with the 3D printer, any interest in another possible project? Is there even room to fit a bumpout onto the side of the AOS? (My car is in Orlando getting some suspension work so I can't look)

Radium King's suggestion is very interesting. It is not a regular catch can.We have already discussed that idea and concluded it was a good idea but space is so limited,it is difficult to execute well. The part Radium King links is quite different to say a JAZ catch can. It is much smaller. This may solve the installation/space issue . It does not solve the problem of the diaphragm splitting? However,if the AOS no longer gets 'swamped' that may prevent the diaphragm getting stretched and soaked in oil. So this may by a vital part of solving this problem. Of course it is not Smog-Legal but what Smog Tech would see/know? There is no need to empty the Grimspeed because it is not a catch can it is an AOS.It is less than $300. The big question is -"Could you use a Grimspeed AOS to completely replace the Porsche part?" https://www.youtube.com/watch?v=HglJqwVJdcY

Far better to avoid the problem by lowering the oil level. Install the fvd sump pan & keep oil level midway between dipstick marks should be 1st step.

Agreed.I have done what you recommend.See post #2.

Quotes source post: 471604

I am thinking the same thing. Add deep sump, put in the same amount of total oil but due to the sump it is lower down. Would be a lot simpler.