Calling experts on AOS/breather
#1
Rennlist Member
Thread Starter
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
Hi.
I am finishing a full rebuild of my -89 Cup car and would like to know your experiences and which way to go concerning the AOS and how it is set up.
The hole has been drilled out in the AOS so either I attach a hose to it and then to a breather tank like lindsey etc.
Or I route it back like stock to before the turbo and put in a restriction like the stock opening in the AOS.
Is there any disadvantages of connecting to a breather tank?
And with the stock routing I have heard of people with higher output engines having issues with the turbo "sucking" oil out through the AOS.
Please tell me your experiences
I am finishing a full rebuild of my -89 Cup car and would like to know your experiences and which way to go concerning the AOS and how it is set up.
The hole has been drilled out in the AOS so either I attach a hose to it and then to a breather tank like lindsey etc.
Or I route it back like stock to before the turbo and put in a restriction like the stock opening in the AOS.
Is there any disadvantages of connecting to a breather tank?
And with the stock routing I have heard of people with higher output engines having issues with the turbo "sucking" oil out through the AOS.
Please tell me your experiences
#3
Rennlist Member
Thread Starter
#5
Rennlist Member
Thread Starter
#6
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
By the time liquid oil will be sucked out of the AOS, some other major problems will have occured.
I suppose the opening is that small because the engine designers probably estimated that blow-by would remain minimal with a K26 turbo running a mere 0.8 bar of boost (will take time to wear out the bores of such a big engine with such a remarkably low specific HP output), and they made the fitting large enough to fit a "standard" size hose. I guess the hole is the same size as on the other 944s, as perhaps they weren't even bothered thinking about making a larger hole for the 944 turbo.
The function of the valve on later cars is to release boost from the AOS line when closing down the throttle when upchanging gears under WOT.
I suppose the opening is that small because the engine designers probably estimated that blow-by would remain minimal with a K26 turbo running a mere 0.8 bar of boost (will take time to wear out the bores of such a big engine with such a remarkably low specific HP output), and they made the fitting large enough to fit a "standard" size hose. I guess the hole is the same size as on the other 944s, as perhaps they weren't even bothered thinking about making a larger hole for the 944 turbo.
The function of the valve on later cars is to release boost from the AOS line when closing down the throttle when upchanging gears under WOT.
#7
Rainman
Rennlist Member
Rennlist Member
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
The AOS is a type of "cyclonic separator".
The smaller the orifice at the exit the higher the "filtration" efficiency can be, all else being equal.
Drilling the hole out is something only to be done when fitting a breather/catch can, as you are then basically transferring the AOS's job to the catch can, and using the AOS as a very overbuilt oil filler.
The smaller the orifice at the exit the higher the "filtration" efficiency can be, all else being equal.
Drilling the hole out is something only to be done when fitting a breather/catch can, as you are then basically transferring the AOS's job to the catch can, and using the AOS as a very overbuilt oil filler.
Trending Topics
#8
Rennlist Member
Thread Starter
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
By the time liquid oil will be sucked out of the AOS, some other major problems will have occured.
I suppose the opening is that small because the engine designers probably estimated that blow-by would remain minimal with a K26 turbo running a mere 0.8 bar of boost (will take time to wear out the bores of such a big engine with such a remarkably low specific HP output), and they made the fitting large enough to fit a "standard" size hose. I guess the hole is the same size as on the other 944s, as perhaps they weren't even bothered thinking about making a larger hole for the 944 turbo.
The function of the valve on later cars is to release boost from the AOS line when closing down the throttle when upchanging gears under WOT.
I suppose the opening is that small because the engine designers probably estimated that blow-by would remain minimal with a K26 turbo running a mere 0.8 bar of boost (will take time to wear out the bores of such a big engine with such a remarkably low specific HP output), and they made the fitting large enough to fit a "standard" size hose. I guess the hole is the same size as on the other 944s, as perhaps they weren't even bothered thinking about making a larger hole for the 944 turbo.
The function of the valve on later cars is to release boost from the AOS line when closing down the throttle when upchanging gears under WOT.
#9
Rennlist Member
Thread Starter
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
The AOS is a type of "cyclonic separator".
The smaller the orifice at the exit the higher the "filtration" efficiency can be, all else being equal.
Drilling the hole out is something only to be done when fitting a breather/catch can, as you are then basically transferring the AOS's job to the catch can, and using the AOS as a very overbuilt oil filler.
The smaller the orifice at the exit the higher the "filtration" efficiency can be, all else being equal.
Drilling the hole out is something only to be done when fitting a breather/catch can, as you are then basically transferring the AOS's job to the catch can, and using the AOS as a very overbuilt oil filler.
So with my setup best would be to hook it up to a breather tank.
Or if routing it back like stock attach a Catch can in between
#10
Rainman
Rennlist Member
Rennlist Member
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
A breather/catch can does the same type of job that the AOS does...separate oil from the air in the crank case, and route fine vapor into the intake.
If you install a breather you don't really need to use the AOS anymore as it was designed - all it serves to do is fill the oil holes in the engine block and act as a "pipe" to feed your breather tank. So since it isn't needed to separate air/oil the cyclonic function isn't needed so the opening can be enlarged.
If you install a breather you don't really need to use the AOS anymore as it was designed - all it serves to do is fill the oil holes in the engine block and act as a "pipe" to feed your breather tank. So since it isn't needed to separate air/oil the cyclonic function isn't needed so the opening can be enlarged.
#11
Rennlist Member
Thread Starter
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
A breather/catch can does the same type of job that the AOS does...separate oil from the air in the crank case, and route fine vapor into the intake.
If you install a breather you don't really need to use the AOS anymore as it was designed - all it serves to do is fill the oil holes in the engine block and act as a "pipe" to feed your breather tank. So since it isn't needed to separate air/oil the cyclonic function isn't needed so the opening can be enlarged.
If you install a breather you don't really need to use the AOS anymore as it was designed - all it serves to do is fill the oil holes in the engine block and act as a "pipe" to feed your breather tank. So since it isn't needed to separate air/oil the cyclonic function isn't needed so the opening can be enlarged.
#12
Rainman
Rennlist Member
Rennlist Member
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
The point of using a breather is that you are venting crankcase pressure to the atmosphere rather than circulating it into the intake tract (which is under vacuum which would help the flow).
A larger opening lets the pressure "breathe out" faster.
A larger opening lets the pressure "breathe out" faster.
#13
Rennlist Member
Thread Starter
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
Is the only gain routing it the stock way that you rid the bad smell and fumes in the enginebay or is there other reasons.
#15
Rennlist Member
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
I drilled my AOS because at high-output, my motor would produce excessive crankcase pressure, which would cause oil leaks, push the dip stick up, etc. Drilling the AOS lowers the crankcase pressure under heavy boost, and eliminates the oil leaks, dip stick issues, etc. As V2 says, however, it also reduces the effectiveness of the Air-Oil-Separator (AOS), allowing more oily mist to escape out the top of the AOS. Because of that, most people who drill the AOS also install a closed-loop catch can, where the hose from the top of the AOS is routed to the catch can, to trap the oil, and another hose from the catch can is routed to the j-boot to vent the pressure. If you use a breather that is not routed back to the j-boot, you'll get a burning oil smell that can be annoying for a street car.
Not sure what you are referring to when you say the turbo might "suck oil" through the AOS, but there are two related issues there. First, when you alter the pressure/vacuum in the crankcase, the oil lubricating the turbo sometimes can't drain fast enough back into the oil pan. That's usually solved by controlling the oil feed to the turbo and reducing pressure in the crank. The other issue is when too much oil vapor spits out the top of the AOS and gets sent to the j-boot, resulting in noticeable amounts of oil in the j-boot and turbo inlet. That is why people use a catch can -- to trap the oil in the can instead of sending it straight into the turbo. A breather vented to atmosphere will also prevent oil from getting to the j-boot, but makes for a smelly car as all that oily pressure fills the air.
Not sure what you are referring to when you say the turbo might "suck oil" through the AOS, but there are two related issues there. First, when you alter the pressure/vacuum in the crankcase, the oil lubricating the turbo sometimes can't drain fast enough back into the oil pan. That's usually solved by controlling the oil feed to the turbo and reducing pressure in the crank. The other issue is when too much oil vapor spits out the top of the AOS and gets sent to the j-boot, resulting in noticeable amounts of oil in the j-boot and turbo inlet. That is why people use a catch can -- to trap the oil in the can instead of sending it straight into the turbo. A breather vented to atmosphere will also prevent oil from getting to the j-boot, but makes for a smelly car as all that oily pressure fills the air.