fast951

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...

Tom M'Guinn

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...

fast951

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.

KSira

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.

Thom

You just answered your own question.

URG8RB8

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

KSira

I have always read that this was oil return from the AOS, but this makes more sense. Are you not worried that when the check valve opens it will push out oil that is on its way back to the engine?

Tom M'Guinn

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....?

URG8RB8

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.

ehall

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?

Tom M'Guinn

You'll have to find a catch can mounting place that allows you to run a line to the pan, with the line angled downward to gravity drain. That might be a bit of a challenge. There aren't many pre-existing options into the pan. Level sender port, big turbo drain banjo, drain plug... what else? Also, I noticed that steam condensation finds its way to the catch can at least as much as oil. It's actually nice getting that out of the motor, so worth running it a while to see if you really want to drain the catch can back to the pan.

That's exactly how it seems to me as well, and the nobler reason I'm hoping to use the side port only when needed. That, and it's a pain to remove the AOS to open the top hole.

URG8RB8

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.

KSira

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.

bebbetufs

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.

KSira

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.