Catch cans and crank pressure
#106
Addict
Rennlist Member
Rennlist
Site Sponsor
Rennlist Member
Rennlist
Site Sponsor
You will have to experiment with the restrictor size. Start as small as possible, you can always drill it out to the next size up if needed.
Drilling and tapping the oil filler cap is an option.
There are many ways to do this. Some work better than others...
Drilling and tapping the oil filler cap is an option.
There are many ways to do this. Some work better than others...
i wonder if a 1/32" restrictor in the line running between the crankcase or the cam tower and the vacuum ports would be small enough to avoid sucking too much oil in the intake. My Supra PCV routed from the cam tower to the intake without any restriction was sucking too much oil.
What about a drilled oil filler cap (or a custom dipstick) to add a second vent near the AOS ??
What about a drilled oil filler cap (or a custom dipstick) to add a second vent near the AOS ??
#107
Rennlist Member
Thread Starter
I think we are focusing on different issues. On my car, the turbo is draining fine at idle and all other times. I did put an oil restrictor in a long time ago, so maybe that's part of it.
My issue is excess pressure building up in the crankcase under sustained boost, which is blowing the dipstick and tube up causing an oily mess. I could open the top of the AOS and probably solve my issue, but (a) I don't want to pull the AOS to do it, and (b) I like the idea of the system functioning exactly as factory until the extra boost requires otherwise. See sketch below of what I'm planning. It is not intended to help the drain at idle -- the only time it will do anything is when the crank pressure (and the pressure in the line) exceed .3psi, at which point it'll vent that pressure to the catch can/j-boot. See sketch below...
My issue is excess pressure building up in the crankcase under sustained boost, which is blowing the dipstick and tube up causing an oily mess. I could open the top of the AOS and probably solve my issue, but (a) I don't want to pull the AOS to do it, and (b) I like the idea of the system functioning exactly as factory until the extra boost requires otherwise. See sketch below of what I'm planning. It is not intended to help the drain at idle -- the only time it will do anything is when the crank pressure (and the pressure in the line) exceed .3psi, at which point it'll vent that pressure to the catch can/j-boot. See sketch below...
#108
Addict
Rennlist Member
Rennlist
Site Sponsor
Rennlist Member
Rennlist
Site Sponsor
I understand your design. Did you already verify that there is pressure in the line between turbo mount and AOS?
Another approach would be a "vented oil dipstick tube". We know there is pressure in the tube to push out the dipstick. Why not vent there? By adding a port to the dipstick tube, you can vent it to catch can. You may need to add a spring to the dipstick to keep it shut and to force air out of the new port.
And for those needing vacuum at idle, they can use it as well.
Lots of good ideas.
Another approach would be a "vented oil dipstick tube". We know there is pressure in the tube to push out the dipstick. Why not vent there? By adding a port to the dipstick tube, you can vent it to catch can. You may need to add a spring to the dipstick to keep it shut and to force air out of the new port.
And for those needing vacuum at idle, they can use it as well.
Lots of good ideas.
I think we are focusing on different issues. On my car, the turbo is draining fine at idle and all other times. I did put an oil restrictor in a long time ago, so maybe that's part of it.
My issue is excess pressure building up in the crankcase under sustained boost, which is blowing the dipstick and tube up causing an oily mess. I could open the top of the AOS and probably solve my issue, but (a) I don't want to pull the AOS to do it, and (b) I like the idea of the system functioning exactly as factory until the extra boost requires otherwise. See sketch below of what I'm planning. It is not intended to help the drain at idle -- the only time it will do anything is when the crank pressure (and the pressure in the line) exceed .3psi, at which point it'll vent that pressure to the catch can/j-boot. See sketch below...
My issue is excess pressure building up in the crankcase under sustained boost, which is blowing the dipstick and tube up causing an oily mess. I could open the top of the AOS and probably solve my issue, but (a) I don't want to pull the AOS to do it, and (b) I like the idea of the system functioning exactly as factory until the extra boost requires otherwise. See sketch below of what I'm planning. It is not intended to help the drain at idle -- the only time it will do anything is when the crank pressure (and the pressure in the line) exceed .3psi, at which point it'll vent that pressure to the catch can/j-boot. See sketch below...
#109
Removed my AOS today to install a bigger fitting. One thing I noticed is that the turbo AOS has a connection to the oil return of the turbo, while the non turbo does not have one. That made me wonder why the turbo is different, you would think that the AOS would work without this line as the non turbo does not have it. That made me wonder if this might actually be part of the turbo oil return. Since the oil return hose is connected below the oil level the drain could be really slow. A non ball bearing turbo has a lot of oil flow.
#111
Drifting
Join Date: Aug 2009
Location: Bangkok, Thailand, Milpitas, CA & Weeki Wachee, FL
Posts: 2,239
Likes: 0
Received 2 Likes
on
1 Post
In my opinion, venting at the oil dipstick tube will be too restrictive, thus the original plan to vent through the cam tower via a check valve as a secondary input into the sealed catch can. This hose will need to be of considerable size. My best guess is 1/2" or -8AN. I don't think 3-8 psi venting through the fairly large cam tower and head drain ports is going to cause much interference with the oil draining back to the pan. Again, theory/speculation, not proven fact. As Tom said, to solve our identical issue, opening up the top AOS port and venting to a proper sealed catch can should solve our issue just fine. When I do my install I am going to install several digital pressure sending units to make measurements. I will of course share the results
#112
#113
Rennlist Member
Thread Starter
That's a potential issue. I'm hoping that gravity will help the oil go down to the drain as intended when it hits the T, and the air will go up and on to the catch can, but that's just a hope. The catch can will protect the motor from sucking it in, but time will tell if this produces too much catch can oil. The other way to think about is to ask which will create more oil in the can -- opening the top of the AOS (which will increase catch can oil by some % ALL of the time) or venting the side port through check valve (which will probably increase the oil flow by a bigger % but only SOME of the time). The answer may depend on how often one is on boost....?
#114
Drifting
Join Date: Aug 2009
Location: Bangkok, Thailand, Milpitas, CA & Weeki Wachee, FL
Posts: 2,239
Likes: 0
Received 2 Likes
on
1 Post
Simple solution to that problem with my catch can anyway. The bottom of the can also has a port for a fitting to be routed back to the oil pan thus continually draining any "caught" oil back to the pan. At first, I am not going to do this as I want to see just how much oil accumulates in a week/month. I am guess not too much.
#115
Addict
Lifetime Rennlist
Member
Lifetime Rennlist
Member
So wait. If the AOS is a centrifugal separator, then widening the top hole should have a negative effect on separating the air and oil. The smaller diameter hole creates greater air pressure, which should cause the air/oil mixture to swirl faster and thus have a greater separation, than should occur with a wider top AOS hole, right?
#116
Rennlist Member
Thread Starter
Simple solution to that problem with my catch can anyway. The bottom of the can also has a port for a fitting to be routed back to the oil pan thus continually draining any "caught" oil back to the pan. At first, I am not going to do this as I want to see just how much oil accumulates in a week/month. I am guess not too much.
So wait. If the AOS is a centrifugal separator, then widening the top hole should have a negative effect on separating the air and oil. The smaller diameter hole creates greater air pressure, which should cause the air/oil mixture to swirl faster and thus have a greater separation, than should occur with a wider top AOS hole, right?
#117
Drifting
Join Date: Aug 2009
Location: Bangkok, Thailand, Milpitas, CA & Weeki Wachee, FL
Posts: 2,239
Likes: 0
Received 2 Likes
on
1 Post
My drain plug is drilled and tapped for 1/8" NPT if I recall correctly. I have an oil temp sensor there now. This could be a option, but like you said, I am not fond of the moisture condensate that accumulates in the can. This project gets more interesting by the minute.
#118
So wait. If the AOS is a centrifugal separator, then widening the top hole should have a negative effect on separating the air and oil. The smaller diameter hole creates greater air pressure, which should cause the air/oil mixture to swirl faster and thus have a greater separation, than should occur with a wider top AOS hole, right?
#119
Burning Brakes
Removed my AOS today to install a bigger fitting. One thing I noticed is that the turbo AOS has a connection to the oil return of the turbo, while the non turbo does not have one. That made me wonder why the turbo is different, you would think that the AOS would work without this line as the non turbo does not have it. That made me wonder if this might actually be part of the turbo oil return. Since the oil return hose is connected below the oil level the drain could be really slow. A non ball bearing turbo has a lot of oil flow.
#120
The stock turbo mount actually has its own sump inside. That is why the turbo drain can be connected below oil level. The line to the AOS allows crank case pressure to this sump. The turbo outlet thus sees the same pressure as it would if it was dumping directly into the sump above oil level. Possibly a bit better since it the vent hose is huge compared to the size of the small sump.