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Catch cans and crank pressure

Old 01-16-2015, 01:50 PM
  #16  
Tom M'Guinn
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Thanks guys. Teddy -- we think alike -- I was going to check the crank pressure but thought I'd clamp a silicon hose over the top of the dipstick tube (with the dipstick removed). Almost seems academic at this point (little elves aren't pushing the stick up under boost) but simple enough to do just to see how much pressure it's seeing. I'll probably put a check valve somewhere just to reduce pressure under boost, though so far it's ok at idle with the factory AOS to J-boost hose. Great input, thanks. I'm sure the old time drag guys did fine with that exhaust venturi, but I'm not quite there yet. While I'm at it I suppose I'll add a catch can too -- trying to sort if I should get the saikou michi can or if I should spend an inordinate amount of time and effort making my own...
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Old 01-16-2015, 02:29 PM
  #17  
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I use a zip tie to hold mine down. I thread it in the dipstick hole and around the upper bracket. They do like to push out at high pressures.

I have a pretty big catch can with multiple vent tubes coming from my custom AOS piece. Works really well.
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Old 01-16-2015, 06:07 PM
  #18  
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Originally Posted by Tom M'Guinn View Post
Thanks guys. Teddy -- we think alike -- I was going to check the crank pressure but thought I'd clamp a silicon hose over the top of the dipstick tube (with the dipstick removed). Almost seems academic at this point (little elves aren't pushing the stick up under boost) but simple enough to do just to see how much pressure it's seeing. I'll probably put a check valve somewhere just to reduce pressure under boost, though so far it's ok at idle with the factory AOS to J-boost hose. Great input, thanks. I'm sure the old time drag guys did fine with that exhaust venturi, but I'm not quite there yet. While I'm at it I suppose I'll add a catch can too -- trying to sort if I should get the saikou michi can or if I should spend an inordinate amount of time and effort making my own...
I originally used the dipstick tube minus the dipstick but it kept leaking and I didn't get consistent results. Intake vacuum is easier... too much work putting in an exhaust scavenging system. What did you mean by this..."'I'll probably put a check valve somewhere just to reduce pressure under boost". The check valve in the vacuum line is to prevent ALL intake pressure from getting into the crankcase.
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Old 01-16-2015, 07:11 PM
  #19  
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Guys at the track drill a hole and use a cotter pin, it is pretty slick. I will get a pic next time I see one.
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Old 01-16-2015, 08:16 PM
  #20  
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I installed this Porsche valve (P/N 94410732400) in the line from my AOS to my saikou catch-can and it seems helps with any over-pressure condition in my track car. I am running E85 and 20.5 PSI boost. This part apparently was installed from the factory on the 1989 951 and the 968RS.


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Old 01-16-2015, 10:21 PM
  #21  
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Originally Posted by Teddy952 View Post
What did you mean by this..."'I'll probably put a check valve somewhere just to reduce pressure under boost". The check valve in the vacuum line is to prevent ALL intake pressure from getting into the crankcase.
I meant I'd connect a hose to the crankcase somewhere (maybe a cam tower plug hole) and put a check valve on it to act like a pop off valve -- i.e., if the crankcase starts to build positive pressure, it will open and relieve the pressure. I'm thinking this will preserve the factory AOS to J-boot system and any suction effect it can create.

I have a hose/valve like the one bw993 posted (somewhere, not on the car), but it doesn't seem like that is intended to do the same thing. And I'm assuming the AOS opening is too restrictive to vent the pressure fast enough since it dumps through a decent size hose in the open j-boot -- i.e., the pressure must be trapped under the AOS opening and not getting out quickly enough, so a second vent with pop-off valve (perhaps recirculated to the j-boot too) seems worthwhile. Won't be able to experiment for a week or two, but will report back.

Re the dipstick, hopefully if I can relieve pressure in the crankcase, then the stick won't pop up anyway -- but that won't stop me from over-engineering something to hold the stick down, and to clamp the tube to the oil pan to better seal it down at the pan. Love the cotter pin idea, but imagine the holes in the tube would make an oily mess over time (and undermine any suction effect from the J-boot)?
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Old 01-17-2015, 02:22 PM
  #22  
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Originally Posted by bw993 View Post
I installed this Porsche valve (P/N 94410732400) in the line from my AOS to my saikou catch-can and it seems helps with any over-pressure condition in my track car. I am running E85 and 20.5 PSI boost. This part apparently was installed from the factory on the 1989 951 and the 968RS.


Hi. I am thinking of doing the same to my car. How did you attach it to the hose to the catch can? Can you post a pic?

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Peder
Sweden
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Old 01-17-2015, 03:32 PM
  #23  
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Originally Posted by peed View Post
Hi. I am thinking of doing the same to my car. How did you attach it to the hose to the catch can? Can you post a pic?

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Peder
Sweden
Buy this hose or fab your own http://www.lindseyracing.com/LR/Pors...OS-102-XL.html

Valve should fit in that smaller hose sticking up after the goose-neck bend
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Old 01-17-2015, 03:40 PM
  #24  
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Well I can't find that old valve I had. Which way does it open? I'm still not seeing how it would help with crankcase pressure, insofar as the hose it sits in has a fairly unobstructed path to atmosphere (i.e., what's the point of a pop-off valve in an open hose). Seems more likely that it opens if vacuum gets too strong in the hose, to prevent sucking too much oil into the j-boot? Anyone know for sure?
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Old 01-17-2015, 07:26 PM
  #25  
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The air control valve is closed under vacuum and opens only when there is enough positive pressure in the AOS system. From what I understand, this valve was originally designed to relieve excess positive pressure in the system due to any moisture or oil buildup that could impact the flow rate through the venturi tube.
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Old 01-17-2015, 10:09 PM
  #26  
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Originally Posted by bw993 View Post
The air control valve is closed under vacuum and opens only when there is enough positive pressure in the AOS system. From what I understand, this valve was originally designed to relieve excess positive pressure in the system due to any moisture or oil buildup that could impact the flow rate through the venturi tube.
Thanks! That may be a useful part for me then, either with a bigger AOS opening or located on a less obstructed vent line from the crankcase.


When it opens, does it dump oil mist into the engine compartment?
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Old 01-18-2015, 02:59 AM
  #27  
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Wonder if you couldn't combine the two concepts. Have a valve that is on the entry to a catch can type setup therefore when there is too much pressure it opens up and whatever blow by matter is caught into the can...or is that too shadetree?
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Old 01-18-2015, 03:05 AM
  #28  
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Originally Posted by 333pg333 View Post
Wonder if you couldn't combine the two concepts. Have a valve that is on the entry to a catch can type setup therefore when there is too much pressure it opens up and whatever blow by matter is caught into the can...or is that too shadetree?
Hope not, that's kind of my emerging plan. The catch can will have one input from the stock aos plumbing, and another input from the cam tower that is only active when the crank pressure opens its check valve. The catch can output will go to the j-boot, so most of the time it will function like the Saikou-Michi but when pressure builds too high in the case it will just have more flow.
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Old 01-18-2015, 04:05 AM
  #29  
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I know Sean / JET951 has been making his own cans and I believe seeing positive results. Maybe PM him too?
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Old 01-18-2015, 05:19 AM
  #30  
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Originally Posted by KSira View Post
Same for me, only slightly oil contaminated water on my expensive ultra exclusive coca cola catch can. Hooking the AOS line to the intake will make vacuum in the engine and increase the sealing of piston rings.

If you are using e85 be aware there may be need for more breathing than running normal gasoline. (This I have been told by several guys running E85, don't remember the technical explanation for why)
My catch can goes connects to my MAF.

IICR a catch can connects back to the intake & a breather is the one with the airfilter on it.
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