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Discussion Starter · #1 ·
I probably posted this in the wrong forum before -

I've been looking at the AOS, and couldn't find any posts or any info online to really describe how it's supposed to work. I've managed to put together an understanding from the service manual - and if my understanding is correct, we should run 2 catch cans - one for the under boost air source, and one for the under vacuum source.
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I believe I've seen some others agree with your assertion that this platform needs 2 catch cans. I don't remember the reasoning, but yeah I've seen it before.
 

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I have two catch cans set up on my fiat. It comes down to preference more than anything. The car does already have an AOS. The second catch can is from your intake runner to the PCV seperate from the turbo. "Idle Suction Pipe" now our cars don't have a throttle body but if you dont want oil heading for your intake valves for another go, catch can is about what you can do.

What i dont like about the OEM system is that it uses the crankcase sump to drain pcv system products back into the engine oil which i think contributes to oil contamination, possibly not by particulates that much more than the blow by already does but what concerns me is water / gasoline. There doesn't seem to be an easy way to rectify this though. I was briefly considering installing a third can to this drain to see what comes out of it but the hose routing is so tight there's just no room and no way to service it.

The only other option would be to remove the factory AOS completely replace it with three catch cans in a row that are plumbed together with a little hose manifold, which is more or less what the AOS is. I think the problem in doing this is you would need a rather beefy PCV check for the boost suction line, which seems to be integral to the AOS.
 

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Discussion Starter · #4 ·
I have two catch cans set up on my fiat. It comes down to preference more than anything. The car does already have an AOS. The second catch can is from your intake runner to the PCV seperate from the turbo. "Idle Suction Pipe" now our cars don't have a throttle body but if you dont want oil heading for your intake valves for another go, catch can is about what you can do.

What i dont like about the OEM system is that it uses the crankcase sump to drain pcv system products back into the engine oil which i think contributes to oil contamination, possibly not by particulates that much more than the blow by already does but what concerns me is water / gasoline. There doesn't seem to be an easy way to rectify this though. I was briefly considering installing a third can to this drain to see what comes out of it but the hose routing is so tight there's just no room and no way to service it.

The only other option would be to remove the factory AOS completely replace it with three catch cans in a row that are plumbed together with a little hose manifold, which is more or less what the AOS is. I think the problem in doing this is you would need a rather beefy PCV check for the boost suction line, which seems to be integral to the AOS.

I've been thinking of ways to do this - since I run e85 and my oil right away smells like e85 even after a fresh oil change. I'm working on a 2 can solution to bypass the oem AOS.
 

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I think without a PCV valve in there properly youre going to get some check engine light.

I think the crankcase drain could be safely plugged or routed to a breather (gut feeling tells me to plug it) but the pcv is essential. I think the AOS actually contains some sort of beefy check valve on the boost line

If you want to do this I think you need to buy a factory 124 spider AOS and cut it up to look. A different forum member wanted to do this some years ago but then basically disappeared. Theres a YouTube video where two dudes say they dissected a 500 abarth AOS box and called the design dumb, but then they didn't explain why.
 

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Discussion Starter · #8 ·
I think without a PCV valve in there properly youre going to get some check engine light.

I think the crankcase drain could be safely plugged or routed to a breather (gut feeling tells me to plug it) but the pcv is essential. I think the AOS actually contains some sort of beefy check valve on the boost line

If you want to do this I think you need to buy a factory 124 spider AOS and cut it up to look. A different forum member wanted to do this some years ago but then basically disappeared. Theres a YouTube video where two dudes say they dissected a 500 abarth AOS box and called the design dumb, but then they didn't explain why.
Yeah I saw the video. I've ordered some parts and have some ideas to try. I am retaining the PCV valve and will have a check on the boost suction line.
 

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I think without a PCV valve in there properly youre going to get some check engine light.

I think the crankcase drain could be safely plugged or routed to a breather (gut feeling tells me to plug it) but the pcv is essential. I think the AOS actually contains some sort of beefy check valve on the boost line

If you want to do this I think you need to buy a factory 124 spider AOS and cut it up to look. A different forum member wanted to do this some years ago but then basically disappeared. Theres a YouTube video where two dudes say they dissected a 500 abarth AOS box and called the design dumb, but then they didn't explain why.
Those guys were John Bussbaum of Tork Motorsports and his sidekick Eddie. I don’t think they considered the PCV as the prime culprit and John crafted a beautiful vapor separator that worked very well. Another post by a different author had a close examination of our PCV and it was a very cheap/crappy part. Replacement had a very positive result! I’m of a vintage that’s used to metal PCVs that could be easily cleaned and reinstalled. Our multiair engine is a unique design and despite the soundness of the principles that drove it has some peculiar issues. Eddie eventually gave up trying to fix his multiair engine and successfully substituted a T-jet cylinder head. AFAIK, he never posted a follow up on the completed tune and some road testing. I’m thinking he just wanted to drive his car!
Best regards
Pete
 

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I just saw a post a few weeks ago or month ago of someone in the forum that had actually installed the two catch cans and added pictures of it. Now, I trying to find that post and for some reason can't find it to save my life, do anyone knows? Have a link to it?
 

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Discussion Starter · #14 ·
If you're considering adding a catch can check out the one I have in my Spider. Has some nice features not found in any other catch can kit that I have found and is a clean installation that looks like it came installed from the factory. https://www.ebay.com/itm/393096635478
That doesn't effectively eliminate the AOS. This style of catch can only works when the PCV "circuit" is in boost mode.
 

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That doesn't effectively eliminate the AOS. This style of catch can only works when the PCV "circuit" is in boost mode.
I went back to the listing to check and they don't claim that it's intended to eliminate the AOS. As in most catch can applications it's intended to capture any oil, for whatever reason, that manages to bypass the AOS and trap it before it can contaminate the intake system.
 

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I probably posted this in the wrong forum before -

I've been looking at the AOS, and couldn't find any posts or any info online to really describe how it's supposed to work. I've managed to put together an understanding from the service manual - and if my understanding is correct, we should run 2 catch cans - one for the under boost air source, and one for the under vacuum source.
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Mine is dry as the Sahara Desert even the intake is dry.
I got some water/oil liquid in the catch can maybe 1 oz, in the fall on a long drive. Mind even my oil level stays flat. But there are those who have such problem, maybe 2 catch can will do. Aliexpress sells them and cheaper if you're not in a hurry. About 1 month shipping.
 
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