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Catch cans and crank pressure

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Old 01-29-2015, 11:53 AM
  #61
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Originally Posted by Tom M'Guinn View Post
After mulling a bunch of options, it finally dawned on me to tee into the vent line going from the AOS to turbo mount. I looked and confirmed the hole in the AOS is much bigger there, and I can put a check valve before the catch can so that port will only vent when the crankcase is under pressure. That's mt latest plan anyway...
Open up the hole in the AOS.

Turbo mount is vented and helps drain the oil from the turbo. You don't want to add any pressure to negate it.
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Old 01-29-2015, 02:10 PM
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Originally Posted by Thom View Post
In what condition was the seal after removal?
I did it with two of them. The seal is just as good
as original, unless you mangle the top.
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Old 01-29-2015, 02:13 PM
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Originally Posted by Thom View Post
Increasing diameter reduces the flow with the same level of vacuum. Not sure how far we want to go... would be nice to have a guy with a 100% stock engine plot vacuum in the AOS pipe in function of load.
Increasing diameter increases flow, but reduces pressure. Restrictions create pressure.
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Old 01-29-2015, 03:11 PM
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Originally Posted by ehall View Post
Increasing diameter increases flow, but reduces pressure. Restrictions create pressure.
Speed will also decrease, letting more of the oil separate from the air and run back to the engine, provided that the hose is higher than the outlet obviously.
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Old 01-29-2015, 03:33 PM
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Originally Posted by ehall View Post
Increasing diameter increases flow, but reduces pressure. Restrictions create pressure.
This is what I said but looking at the equation another way.
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Old 01-29-2015, 05:24 PM
  #66
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Originally Posted by fast951 View Post
Open up the hole in the AOS.

Turbo mount is vented and helps drain the oil from the turbo. You don't want to add any pressure to negate it.
What effect would connecting the turbo mount vent directly to a vacuum source instead of the side port on the AOS have? If that is just a vent, no liquid oil, then connecting it to the intake manifold with a check valve inline will assist with draining the oil through the turbo....?
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Old 01-30-2015, 02:29 AM
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Originally Posted by Thom View Post
This is what I said but looking at the equation another way.
Well, flow and restriction only work one way, but okay.
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Old 01-30-2015, 02:44 AM
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Originally Posted by fast951 View Post
Open up the hole in the AOS.

Turbo mount is vented and helps drain the oil from the turbo. You don't want to add any pressure to negate it.
Thanks, I hear you. The approach I have in mind would only decrease pressure in mount/drain -- never increase it. The extra line would have a check valve, so the pressure in the drain/mount would be identical to stock unless/until the crankcase has positive pressure. When the crankcase has positive pressure, the check valve will open and reduce the pressure in the crankcase (and therefore the pressure in the turbo mount/drain). Or am I missing something?
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Old 01-30-2015, 05:39 AM
  #69
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If the pipe between the turbo mount and the AOS is a "drain" pipe, then we want vacuum in it. By the time some check valve added in the system opens it means there will be pressure in the system whereas we only want vacuum.
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Old 01-30-2015, 11:39 AM
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Originally Posted by ehall View Post
I did it with two of them. The seal is just as good
as original, unless you mangle the top.
My seal was in good condition too, but it is very brittle. I took it out and it broke.

Looks like it is made of buna rubber that doesn't like synthetic oils.

Very simple seal so replacement should not be a problem.
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Old 01-31-2015, 04:42 AM
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Originally Posted by URG8RB8 View Post
Harry:

If you take that SS CC concept and then run an additional line from the top of the cam tower with a 1/3 psi check valve to remove the additional positive pressure it should do the trick. I was over at Tom's yesterday and we discussed this quite a bit. I have many cool fittings and valves at work along with high temp Teflon thick wall tubing. We can make something up pretty quickly. Be interesting to see just how much oil vapor is released from the top of the cam tower. Our assumption will be volume. How large of a line do we need to quickly and instantly dump all of the positive pressure? The cam tower plugs will only except around 1/4 NPT, might have to use two. Could have a giant custom plug with hose nipple machined if necessary. I would think 1/2" or -8 should be more than sufficient.
I too have considered this many times but I have one big concern. We know from the 928 that the crank can push oil up through the return chutes and load up the heads. This can supposedly cause problems by leaving too little in the sump. The 944 8V has positive pressure in the cam tower (thus the relatively common problem of blowing out cam tower gaskets). This could help push the oil back to the sump. Could not relieving this pressure cause problems, and possbly flood the catch can and/ or the intake?

On the other hand it could alleviate the problem with the cam tower gaskets.
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Old 01-31-2015, 10:22 AM
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This is the fitting I used in place of the cam plugs.

http://www.summitracing.com/parts/fra-460618
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Old 01-31-2015, 02:22 PM
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Thanks for the link Ted, nice and simple adaptor! I assume you are venting your cam tower all ready since you are using this fitting. Have you experienced any of the issues mentioned above? How much oil blow by is coming from the cam tower. I would assume not that much, but you know what that gets you. Which check valve did you select for this line?
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Old 01-31-2015, 02:36 PM
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Originally Posted by Teddy952 View Post
This is the fitting I used in place of the cam plugs.

http://www.summitracing.com/parts/fra-460618
Doesn't this adapter hit the cam cover casting (where the Porsche script is)?

I've bought this kind of M18x1.5 adapter to fit my pcv and couldn't screw it full...
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Old 02-01-2015, 10:54 AM
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Originally Posted by URG8RB8 View Post
Thanks for the link Ted, nice and simple adaptor! I assume you are venting your cam tower all ready since you are using this fitting. Have you experienced any of the issues mentioned above? How much oil blow by is coming from the cam tower. I would assume not that much, but you know what that gets you. Which check valve did you select for this line?
Initially I used the cam tower port as a source to monitor crankcase pressure/vacuum. I then tried connecting the cam port to one of the smaller intake vacuum ports with a check valve inline. I wanted to introduce vacuum to the crank case and the check valve would block the boost from entering. The test was very short lived.... after a quick drive I noticed a very little amount of blueish exhaust smoke. I believe the intake was pulling too much oily vapors from the cam tower port or maybe it sucked up some oil. At the moment I'm not using any of the cam ports for venting blow by. I would like to eventually but I haven't found a decent solution.

Here is where I got my check valves from.
http://www.usplastic.com/catalog/def...arentcatid=870

I used brass because once I found a solution I was going to use copper tubing with some compression fitting to make a custom venting system. Some of the brass valves have a 1/3 PSI cracking pressure. Maybe using a couple cam ports with these low PSI cracking valves will work? I don't think the cam ports are a good source for pulling vacuum on the crankcase, they maybe better at relieving pressure though. Once the crankcase pressure got over 1 PSI these valves should pop open and flow out cam tower port and into a catch can. I'm concerned about what will flow out of the ports though. I would assume oily vapors but I don't know for sure.
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