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PCV hole in intake manifold
https://www.slantsix.org/forum/viewtopic.php?t=33235		 Page 1 of 1
Author:  Eric W [ Fri Jan 09, 2009 2:09 am ]
Post subject:  PCV hole in intake manifold
Does anybody have the exact size of the hole in the intake manifold for the PCV provision under the carburetor mount? The manifold that came on my '83 aluminum intake did not have a provision for it, since it used the Holley 1945. Reed drilled a hole in the manifold so the PCV will work with my 1920, but since I have access to any size reamer I want at work, I thought I would ream the hole to the correct size. Thanks.
Author:  68barracuda [ Fri Jan 09, 2009 4:51 am ]
Post subject: 
Hi Eric is the hole in #6 runner?

If so If I may make a suggestion - plug it and dril a hole in the side plenum of the plenum - will help in a way to improve mixture distro - if it is already there - ignore my post
:P
Author:  Eric W [ Fri Jan 09, 2009 10:07 am ]
Post subject: 
Its the hole under where the carburetor mounts, not on any of the runners. Its maybe 3/16 to 1/4 inch, but I would like the exact size.
Author:  SlantSixDan [ Fri Jan 09, 2009 10:41 am ]
Post subject: 
Pretty sure it's ΒΌ", but it's not critical - the PCV valve is the metering point in the system.

Keep in mind that hole is not used for PCV on carbs made after about '67-'69 (it's in that year range, not sure exactly when). That's when the PCV port was moved over to the inboard side of the BBS and 1920 carburetors, which gave better overall mixture distribution and required no separate pass-thru port in the carb mounting pad on the intake manifold. That pass-thru, however, is used for manifold vacuum to the thermostatic air cleaner on 1920 thru '72, BBS thru '74.
Author:  Eric W [ Fri Jan 09, 2009 10:45 am ]
Post subject: 
Oh. Well, nevermind then, thanks Dan.
Author:  Eric W [ Fri Jan 09, 2009 6:15 pm ]
Post subject: 
Wait a minute: I thought if one where to put the carburetor gasket on backwards, the PCV would not work, hence the gasket only working one way?
Author:  SlantSixDan [ Fri Jan 09, 2009 9:56 pm ]
Post subject: 
Starting in '73 the (new that year) gasket does not chanellise vacuum to the underside of the carb, and cannot be installed "backward" or "upside down" .
Author:  Eric W [ Fri Jan 09, 2009 11:55 pm ]
Post subject: 
For a Holley 1945, yes. That gasket is solid with no hole. For my 1920, the large connection for the pcv hose (on the inboard side) connects to a passageway under the carburetor body that goes to....the hole in the gasket/hole in the manifold. Tomorrow I will flip the gasket to see if the pcv dosn't work (so the hole is covered). There has to be a reason the carb base gasket has forward and top printed on it.
Author:  SlantSixDan [ Sat Jan 10, 2009 10:35 am ]
Post subject: 
Quote:
For a Holley 1945, yes. That gasket is solid with no hole. For my 1920, the large connection for the pcv hose (on the inboard side) connects to a passageway under the carburetor body that goes to....the hole in the gasket/hole in the manifold.
I've taken apart a lot of Holley 1920s, and never seen one like this what you describe. I think if you look closer, you'll see it's not as it first appeared to you.
Quote:
There has to be a reason the carb base gasket has forward and top printed on it.
Yeah, because that directionality is important on pre-'73 carbs.
Author:  Eric W [ Sat Jan 10, 2009 4:58 pm ]
Post subject: 
Well, I stand corrected. :oops: Thanks Dan, and thanks for being civil with me. 8)
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