Catch cans and crank pressure
02-06-2015, 01:54 PM
#121
Burning Brakes
Interesting though alto I am not sure I see the logic. Having the same pressure in the engine mount, the oil drain must still overcome the restriction of the oil in the oil pan. Since the pressure in the engine mount and engine is the same it should cancel each other out, and venting the AOS to create zero pressure in the engine and turbo mount should not make a difference.
02-06-2015, 02:23 PM
#122
Yes, but as the turbo drain is sumped and vented there will be no build up of back pressure in the drain pipe like there could be if it were closed. Thus the turbo simply sees crank case pressure on the outlet side. The oil in the pipe will be level with the oil in the oil pan. The problem comes if this crank case pressure is excessive of course.
EDIT: I have had the engine mount vent blocked of and had no problem with using it like this. This was with a ball bearing turbo which have very little oil flow. (Not my doing this block of, that's why it will be removed)
Have now installed a 1" fitting so engine pressure should not be a problem and hopefully will not affect how how the AOS works
02-06-2015, 03:34 PM
#123
Agreed, but it is not the same as having the oil return above oil level. I get your point of the turbo seeing it like this. Even with the sump and the pressure vent from the oil sump in the engine mount. The oil still have to overcome the restriction of having oil return below oil level. My concern and point was that with constant high RPM there could be to little time for the sump in the engine mount to drain and it could overflow in to the AOS. Nothing would make me happier than this not being the case tho, could just be me worrying to much. Having spent time wrenching on my 944 my faith in Porsche engineers have faltered slightly.
The only moment there may be pressure in the line between the J-boot and the AOS is when the throttle is abruptly closed and the recirculating valve releases pressurized air back into the J-boot (eg when going WOT through gears).
With that said, the only reason there is an air line between the turbo oil outlet and the AOS is to use the vacuum expected in the crankcase to drain lubricating oil out of the turbo.
02-06-2015, 04:00 PM
#124
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Would not the speed be driven by pressure difference and a greater difference by opening up the top of the AOS should help the oil separate from the air? I would think the limit in the stock AOS is to avoid sucking up oil to the intake when the stock solution creates vacuum.
In essence, a larger opening may help with crank case pressure, at the cost of failing to separate air from oil as well. It seems it would be a trade off. It might be best to open the hole, but add an additional catch can. I'm just speculating though.
02-06-2015, 04:46 PM
#125
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The stock breathing system is designed so that the AOS is put constantly under vacuum as air is being ingested by the compressor when the engine is running under load, and on a stock engine with correctly-sealing pistons rings, it works pretty damn well.
The only moment there may be pressure in the line between the J-boot and the AOS is when the throttle is abruptly closed and the recirculating valve releases pressurized air back into the J-boot (eg when going WOT through gears).
With that said, the only reason there is an air line between the turbo oil outlet and the AOS is to use the vacuum expected in the crankcase to drain lubricating oil out of the turbo.
The only moment there may be pressure in the line between the J-boot and the AOS is when the throttle is abruptly closed and the recirculating valve releases pressurized air back into the J-boot (eg when going WOT through gears).
With that said, the only reason there is an air line between the turbo oil outlet and the AOS is to use the vacuum expected in the crankcase to drain lubricating oil out of the turbo.
02-06-2015, 05:06 PM
#126
Without the stock intake snorkel, the level of vacuum at the AOS port, if any, is too low to measure with a traditional automotive vacuum gauge -- at least on my car. And when you remove the snorkel and crank the boost, the pressure coming from the AOS overwhelms whatever scavenging effect coming from the j-boot. Agree it works fine in the stock set up, but with typical mods, you end up with pressure in the vent line.
I'm not sure the BOV would ever pressurize that vent line though -- when the BOV opens, the pressure has a hu's ge and close exit route back through the MAF/filter. With the great big opening so close, it seems unlikely that much pressure would find it's way down a foot long 18mm hose, into the AOS, and on to the vent line. Maybe, but I dunno....
02-06-2015, 05:49 PM
#127
Drifting
Here's what we did to solve the crankcase pressure issue on my car. This completely solved the issue.
My plan was to make the turbo oil drain connect directly to the oil pan and eliminate the existing tee going into the AOS. The AOS has been opened up without removing from the car. Just made the hole larger which worked as hoped.
Add a new vent from the valve cover to the now freed up 2nd AOS inlet. The banjo mentioned in Tom's post is a good way to attach.
"...the drain port that connects to the turbo mount ..." is not a drain port. It
is an inlet into the AOS, one of the 2 inlet ports I showed you located at the top of the AOS and angled to attach the oil to the AOS walls and create a cyclone effect within the unit. The factory turbo mount has a chamber/reservoir to catch the oil draining from the turbo. At the bottom it has a drain to the pan. Without the vent at the top oil would not flow freely in and
out of the chamber.
Very happy with the results, especially while using all factory parts!
My plan was to make the turbo oil drain connect directly to the oil pan and eliminate the existing tee going into the AOS. The AOS has been opened up without removing from the car. Just made the hole larger which worked as hoped.
Add a new vent from the valve cover to the now freed up 2nd AOS inlet. The banjo mentioned in Tom's post is a good way to attach.
"...the drain port that connects to the turbo mount ..." is not a drain port. It
is an inlet into the AOS, one of the 2 inlet ports I showed you located at the top of the AOS and angled to attach the oil to the AOS walls and create a cyclone effect within the unit. The factory turbo mount has a chamber/reservoir to catch the oil draining from the turbo. At the bottom it has a drain to the pan. Without the vent at the top oil would not flow freely in and
out of the chamber.
Very happy with the results, especially while using all factory parts!
02-06-2015, 05:56 PM
#128
Theoretically no. A larger opening creates more flow but less pressure. The smaller hole causes the same amount of air to force it's way through restriction, thus causing greater pressure. The higher the pressure the harder the air/oil mix will swirl inside the AOS. That's what allows it to separate.
In essence, a larger opening may help with crank case pressure, at the cost of failing to separate air from oil as well. It seems it would be a trade off. It might be best to open the hole, but add an additional catch can. I'm just speculating though.
In essence, a larger opening may help with crank case pressure, at the cost of failing to separate air from oil as well. It seems it would be a trade off. It might be best to open the hole, but add an additional catch can. I'm just speculating though.
02-06-2015, 06:05 PM
#129
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Here's what we did to solve the crankcase pressure issue on my car. This completely solved the issue.
My plan was to make the turbo oil drain connect directly to the oil pan and eliminate the existing tee going into the AOS. The AOS has been opened up without removing from the car. Just made the hole larger which worked as hoped.
Add a new vent from the valve cover to the now freed up 2nd AOS inlet. The banjo mentioned in Tom's post is a good way to attach.
"...the drain port that connects to the turbo mount ..." is not a drain port. It
is an inlet into the AOS, one of the 2 inlet ports I showed you located at the top of the AOS and angled to attach the oil to the AOS walls and create a cyclone effect within the unit. The factory turbo mount has a chamber/reservoir to catch the oil draining from the turbo. At the bottom it has a drain to the pan. Without the vent at the top oil would not flow freely in and
out of the chamber.
Very happy with the results, especially while using all factory parts!
My plan was to make the turbo oil drain connect directly to the oil pan and eliminate the existing tee going into the AOS. The AOS has been opened up without removing from the car. Just made the hole larger which worked as hoped.
Add a new vent from the valve cover to the now freed up 2nd AOS inlet. The banjo mentioned in Tom's post is a good way to attach.
"...the drain port that connects to the turbo mount ..." is not a drain port. It
is an inlet into the AOS, one of the 2 inlet ports I showed you located at the top of the AOS and angled to attach the oil to the AOS walls and create a cyclone effect within the unit. The factory turbo mount has a chamber/reservoir to catch the oil draining from the turbo. At the bottom it has a drain to the pan. Without the vent at the top oil would not flow freely in and
out of the chamber.
Very happy with the results, especially while using all factory parts!
02-06-2015, 06:19 PM
#130
Burning Brakes
I'm not sure I understand how you plumbed it though. Did you block the vent from the turbo mount, or did you tee into it?
Nice to hear you're happy with the modifications. I suppose you're not getting a lot of oil in the intake then? If not I was likely wrong in my assumption that oil could be whipped up by the crank and pushed up the returns from the head in left hand turns. How hard have you been pushing the car with the mod. Any long track sessions with long left hand turns or hard breaking into long turns?
02-06-2015, 06:39 PM
#131
Rennlist Member
Thread Starter
Here's what we did to solve the crankcase pressure issue on my car. This completely solved the issue.
My plan was to make the turbo oil drain connect directly to the oil pan and eliminate the existing tee going into the AOS. The AOS has been opened up without removing from the car. Just made the hole larger which worked as hoped.
Add a new vent from the valve cover to the now freed up 2nd AOS inlet. The banjo mentioned in Tom's post is a good way to attach.
"...the drain port that connects to the turbo mount ..." is not a drain port. It
is an inlet into the AOS, one of the 2 inlet ports I showed you located at the top of the AOS and angled to attach the oil to the AOS walls and create a cyclone effect within the unit. The factory turbo mount has a chamber/reservoir to catch the oil draining from the turbo. At the bottom it has a drain to the pan. Without the vent at the top oil would not flow freely in and
out of the chamber.
Very happy with the results, especially while using all factory parts!
My plan was to make the turbo oil drain connect directly to the oil pan and eliminate the existing tee going into the AOS. The AOS has been opened up without removing from the car. Just made the hole larger which worked as hoped.
Add a new vent from the valve cover to the now freed up 2nd AOS inlet. The banjo mentioned in Tom's post is a good way to attach.
"...the drain port that connects to the turbo mount ..." is not a drain port. It
is an inlet into the AOS, one of the 2 inlet ports I showed you located at the top of the AOS and angled to attach the oil to the AOS walls and create a cyclone effect within the unit. The factory turbo mount has a chamber/reservoir to catch the oil draining from the turbo. At the bottom it has a drain to the pan. Without the vent at the top oil would not flow freely in and
out of the chamber.
Very happy with the results, especially while using all factory parts!
02-06-2015, 06:45 PM
#132
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Thread Starter
I agree with your view on the breathing system.
I'm not sure I understand how you plumbed it though. Did you block the vent from the turbo mount, or did you tee into it?
Nice to hear you're happy with the modifications. I suppose you're not getting a lot of oil in the intake then? If not I was likely wrong in my assumption that oil could be whipped up by the crank and pushed up the returns from the head in left hand turns. How hard have you been pushing the car with the mod. Any long track sessions with long left hand turns or hard breaking into long turns?
I'm not sure I understand how you plumbed it though. Did you block the vent from the turbo mount, or did you tee into it?
Nice to hear you're happy with the modifications. I suppose you're not getting a lot of oil in the intake then? If not I was likely wrong in my assumption that oil could be whipped up by the crank and pushed up the returns from the head in left hand turns. How hard have you been pushing the car with the mod. Any long track sessions with long left hand turns or hard breaking into long turns?
02-06-2015, 07:31 PM
#133
Drifting
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LR also modified my FL car similar to what Gorge just described. I have an independent drain for the turbo going straight to the oil pan via a -10 or -12 AN line below the oil level. It has been so long ago I can't remember. Mike welded on an AN nipple to the pan when he put the barn door in. It also has the giant "overkill" 1" vent upgrade kit to there catch can which I don't like as everything will smell nasty. No idea how well this system works since I have never started the car. I did not pay attention to what they did about the vent line. If I ever go home this year I will take some pics.
02-06-2015, 08:19 PM
#134
Rennlist Member
Thread Starter
That's odd... your 3.0 is pretty much like mine was in its early days and I did not have this issue when using the stock airbox. I really can't see any other reason than worn out piston rings/bores to explain the issue, although I certainly hope I'm wrong...
On a stock set up, when you close the throttle abruptly after having gone WOT the barn door AFM will close and the pressurized air will go to the AOS - later cars have a pressure release valve on the rubber section of the breather line plugged onto the AOS cover.
On a stock set up, when you close the throttle abruptly after having gone WOT the barn door AFM will close and the pressurized air will go to the AOS - later cars have a pressure release valve on the rubber section of the breather line plugged onto the AOS cover.
Good point about the flapper on stock cars -- been so long I always think in terms of having a MAF...
