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Old 10-03-2019, 03:02 PM   #1
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Alternatives to the Motorsport AOS?

I currently run the Porsche motorsport AOS since I clearly have way too much money to spend. However, I dread the day that it fails. I am also trying to setup my friend's boxster so he can join me on the track. He's too cheap to buy the upgraded AOS.

What do you guys (or spec boxster guys) use? I imagine a catch can could be setup... I'm just wondering if there's a common setup that people use or could recommend. Anybody have pics of a catch can setup on the 986?

Thanks!
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Old 10-03-2019, 04:04 PM   #2
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Honestly, to date, I'm quite happy with my grunge solution. Im using the stock AOS. I took a hunk of clear, braided, wire - reinforced hose and used it to replace the short hose from the AOS to the plenum. I made a single "coil" of it, that falls well below the intake.
The net effect is that when oil that would normally overwhelm the AOS and end up in the intake gets into the hose, it drops to the bottom of the coil. Because the hose is clear, I can see when there's oil in it, and I pull it off and drain it.

It's worked well SO FAR.

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Old 10-03-2019, 08:32 PM   #3
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Most of the Spec Boxster drivers that I know just run the inexpensive OEM part and replace it as needed.
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Old 10-03-2019, 08:58 PM   #4
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I ran the original 98 AOS for 8 years and 80 track days in my 2.5L BSX Boxster. An oil overfill by my "trusted" shop resulted in it's demise and I replaced it with stock OEM and ran another 40 track days with the new one.

My brother and I ran identical BSX cars at the pointy end of the time sheet in PCA Time Trials with around 200 track days between us. The stock OEM AOS proved to be very reliable. Our experience suggests that if you keep the oil level *just at the top of the gauge or dip stick you will not likely have a problem running stock. An oil overfill kills em quick.
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Old 10-03-2019, 11:05 PM   #5
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dang. I feel like a chump running the Motorsport aos. You guys don’t even get puffs of smoke out the exhaust in hard corners?

All the better though. Less concern about blowning up the expensive aos. Thanks guys for your responses.
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Old 10-04-2019, 05:03 AM   #6
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Quote:
Originally Posted by maytag View Post
Honestly, to date, I'm quite happy with my grunge solution. Im using the stock AOS. I took a hunk of clear, braided, wire - reinforced hose and used it to replace the short hose from the AOS to the plenum. I made a single "coil" of it, that falls well below the intake.
The net effect is that when oil that would normally overwhelm the AOS and end up in the intake gets into the hose, it drops to the bottom of the coil. Because the hose is clear, I can see when there's oil in it, and I pull it off and drain it.

It's worked well SO FAR.

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That's a great idea! How much oil do you find? Does your oil level seem to stabilize at a certain point. For example I have heard folks with a catch can say that if they top off their oil, a few ounces quickly gets into the catch can and then no more.

On my Boxster, I accidentally overfilled my oil before my first track day in 2013 and blew a huge smoke bomb. I left early, and fixed my oil level (dropped the filter and drained the oil out of the canister) and never had any trouble with that AOS in 6 years of track days, and in fact that same AOS is still on the car.

I now have the 2 QT LN Deep sump and run (well ran since I have a Cayman now that I track) the oil level about 1/2 down between the two digital tick marks (2000 S) and what I have found is that if I top off the oil, for me, although I don't blow any smoke bombs, it goes down until about the middle and then stabilizes.

I have seen plenty of smoke bombs from other 986 Boxsters and some 987.1 Caymans, but I've been lucky and never had one after that first scary one
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Old 10-04-2019, 09:34 AM   #7
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I was under the impression that most Spec Boxsters simply remove the AOS and block off the opening.

Am I wrong?
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Old 10-04-2019, 09:42 AM   #8
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I was under the impression that most Spec Boxsters simply remove the AOS and block off the opening.

Am I wrong?
Yes...……..
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Old 10-04-2019, 10:18 AM   #9
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I run a moroso catch can. Pretty much every track day results in 118ml in the catch can. Street driving, almost nothing.

I'm still thinking about devising either an electrical or scavenge/tandem pump to delete the AOS.
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Old 10-04-2019, 10:38 AM   #10
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Originally Posted by Greg Holmberg View Post
I was under the impression that most Spec Boxsters simply remove the AOS and block off the opening.

Am I wrong?
I would never just block the opening. Your crankcase MUST vent. On many race cars and bikes we've simply vented to the header, or out the back. But I've also read that these low- tension rings require some vacuum to seal properly. I can't confirm, but I buy it.
But don't ever just seal it off.


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Old 10-04-2019, 11:22 AM   #11
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But I've also read that these low- tension rings require some vacuum to seal properly. I can't confirm, but I buy it.
That is correct.
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Old 10-04-2019, 05:52 PM   #12
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I just take an extra AOS with me to the track, that way if it shoots craps I don't have to pack up for the w/e.
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Old 10-05-2019, 05:10 AM   #13
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I just take an extra AOS with me to the track, that way if it shoots craps I don't have to pack up for the w/e.
I've read about this before. Maybe fron you? It's a good idea and I've started packing a spare as well, just in case.

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Old 10-05-2019, 01:01 PM   #14
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I pack a spare just in case. Engines seem to react differently to oil levels. My previous motor never blew a bomb no matter what level I ran. It did blow up at the track mind you. This new engine blew a huge bomb on my first outing. Rather embarrassing as the red flags came out. They thought that I was on fire! Since then, I run at about 2 bars over the bottom notch. The oil expands as it heats up but I’ve not had any further problems.
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Old 10-06-2019, 03:11 AM   #15
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So like a few other owners the boxster I bought had this strange issue of on long left bends or when driving hard and changing gears
the car would produce a smoke screen that James Bond would be proud of!!
at first I thought the AOS was getting tired so that was changed for another original but still the same thing happened .
its quite obvious that what was happening is the AOS is getting overwhelmed and neat oil is being pulled into the inlet manifold
so the fix I made was to put an oil catch tank plumbed in between the AOS and the inlet but a catch tank with 3 ports two at the top 15mm and one at the bottom corner 8mm
‘this 8mm port was connected to a one way valve then plumbed into the oil filler pipe of the engine this avoids the sump being over vacuumed by the inlet giving the same symptoms as a failed AOS and making the oil filler cap impossible to remove when the engines running .
so on test no white smoke from the exhaust at all...... NOTHING
on inspection of the catch tank there was evidence of oil being sucked up and evidence that this had simply drained back into the sump when cruising as the vacuum was low enough for the one way valve to let the oil drain back
the catch tank is mounted in the boot behind the carpet so can’t be seen and apart from periodic glances is fit and forget with no oil being lost from the system
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Old 10-06-2019, 06:25 AM   #16
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So like a few other owners the boxster I bought had this strange issue of on long left bends or when driving hard and changing gears

the car would produce a smoke screen that James Bond would be proud of!!

at first I thought the AOS was getting tired so that was changed for another original but still the same thing happened .

its quite obvious that what was happening is the AOS is getting overwhelmed and neat oil is being pulled into the inlet manifold

so the fix I made was to put an oil catch tank plumbed in between the AOS and the inlet but a catch tank with 3 ports two at the top 15mm and one at the bottom corner 8mm

‘this 8mm port was connected to a one way valve then plumbed into the oil filler pipe of the engine this avoids the sump being over vacuumed by the inlet giving the same symptoms as a failed AOS and making the oil filler cap impossible to remove when the engines running .

so on test no white smoke from the exhaust at all...... NOTHING

on inspection of the catch tank there was evidence of oil being sucked up and evidence that this had simply drained back into the sump when cruising as the vacuum was low enough for the one way valve to let the oil drain back

the catch tank is mounted in the boot behind the carpet so can’t be seen and apart from periodic glances is fit and forget with no oil being lost from the system
That sounds PERFECT. I couldn't find a good catch can to do this with. Can you share what you used?

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Old 10-06-2019, 06:36 AM   #17
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Hi I used this catch tank (uk eBay number 330674802885)
And this ( uk eBay number 293260351570)
As it has a ball bearing not a piece of rubber
Let me know if you need any more information
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Old 10-06-2019, 12:00 PM   #18
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I have a friend who races spec and his dad and him use a catch can and block off the the intake vent. They've been racing for years like that with no problems. My friend is the only certified installer for the L&N IMS solution in Texas. I followed his advice and did the same to my rallycross boxster. I forgot to vent the catch can and oil started coming out the crank seals. Besides that, it's worked pretty good for me. I've heard from another friend that you lose power by using a catch can but I don't feel it. I also don't see my friend's car any slower than the rest. Just my .02
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Old 10-07-2019, 12:38 AM   #19
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My understanding of the AOS, vacuum and low tension rings is this. The primary advantage of low tension rings is free HP due to reduced friction on cylinder walls. The second part is this, The AOS is an emission device. It is there to capture and reduce blow-by from combustion in the crankcase, and it works like this.
The pressure from combustion helps seal the rings against the cylinder and piston ring lands. As the piston approaches BDC energy is spent and pressure in the cylinder begins to decrease. As cylinder and crankcase pressures approach equalization it causes the rings to lose contact resulting in blow-by. Vacuum in the crankcase supplied by the AOS allows the low tension rings to maintain contact further down the stroke resulting in reduced blow-by.
So if you don't have to smog your car, the AOS is not required, you will simply have a little more blow-by. This is simplified for understanding, and does not address leakage and trapped pressure between the oil control rings that contribute to the problem. Bottom line if you have an off road only car, Stick a vent cap on the oil fill tube and rock and roll.
Of course I could be wrong.....

Last edited by 911monty; 10-07-2019 at 01:09 AM.
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Old 10-07-2019, 07:43 AM   #20
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no thoughts on using a tandem pump from a 9x7 to create vacuum in crankcase and just eliminate the aos.
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