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Ported, Non-ported, And "Timed Vacuum"

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  • Fuel System: Ported, Non-ported, And "Timed Vacuum"

    Recently, we high jacked a poor guy's thread ("Ignition timing") who was just trying to hook up his new carb. The issue became whether Stude carbs have ported or un-ported vacuum slits, for vacuum to the distributor's vacuum advance (VA). The technical difference is whether the horizontal slit is located, above or below the butterflies (at idle); ported is above, and un-ported is below.

    I said un-ported since, though I have not ran a OEM carb for decades, I recalled well, when unplugging the VA hose from the carb nipple, there was a strong vacuum leak. That leak, if not plugged quickly (i.e. finger over it) would result in idle speedup a few hundred RPMs initially, then stumbling. If plugged, the RPM would drop down so slow it would seem about to die.

    Others said ported, and recalled none of the above; said nothing changed whether the VA hose was connected or not.

    I don't trust anyone's memory, esp. my own, so I looked at an old WCFB, which appeared to be non-ported. Several others ignored that observation, and suggested other ways to determine. Then we all took our marbles and went home. Later, a demi-god spoke.

    This morning, I looked very, very, very closely at the 1956 WCFB again, also a 1970s AFB, a 1980s Holley, and new Edlebrock. I used a scribe to trace the closed butterfly position, in relation to the vacuum slit. I also used a strong pen-lite to see down inside the venturi.

    After looking at the carbs, then refreshing my memory on "timed vacuum" in a 1980s Holley manual I'd had for years, I now have a possible explanation for the above: There is ported vacuum, and there is ported vacuum.

    The WCFB's slit is even with the butterfly, BUT the edge of the butterfly is angled upward & away from the slit, so the lower edge is effectively all that is below the slit. So technically, it is PORTED. The AFB slit is maybe 1/64" above where the WCFB's is, in relation to the butterfly, so it too is PORTED. The Edlebrock & Holley's slits are near 1/16" above the butterfly, so definitely PORTED.

    The difference is in timing; how far off idle, before the slits become un-ported. For the WCFB or AFB to stay ported, they must idle very slow, say around 550-600 RPM. Much above that and they become un-ported. The Edlebrock & Holley would probably still be ported at anything less than around 1200 RPM. Further, the OEM carb's transition to un-ported is likely much quicker due to the position of the butterfly, in relation to the slit when it passes it.

    The 59-64 Shop Manual says time the V8s at 600 RPM then readjust the idle to 550. That accounts for the different memories. I have set my Studes to idle at 750-800 is cool weather, and 850-900 in AC weather for as long as I can recall. At those idle speeds, the vacuum exists as I recall above. But for others, who set their idle around 550, there is likely little or no vacuum, as y'all recall.

    However, in light of the above, I MUST CONCEDE, technically speaking, all Stude carbs appear to be PORTED. (Though I am unsure whether a 56J with WCFB will idle with the butterflies locked in the bores.)
    Last edited by JoeHall; 08-03-2013, 02:11 PM.

  • #2
    Joe:
    I agree with your discussion, except that to me ported is ported and manifold is manifold; ie it doesn't depend on idle speed, it depends on where the vacuum port is. If it is above the throttle plate, it is ported (even if adjusting idle speed moves the throttle plate to "expose" the vacuum port).
    Howard - Los Angeles chapter SDC
    '53 Commander Starliner (Finally running and driving, but still in process)
    '56 Golden Hawk (3 speed/overdrive, Power steering - Running, but not yet driving)
    '58 Packard Hawk. A partially restored car that was not completely assembled.

    Comment


    • #3
      Originally posted by JoeHall View Post
      Recently, we high jacked a poor guy's thread ("Ignition timing") who was just trying to hook up his new carb. The issue became whether Stude carbs have ported or un-ported vacuum slits, for vacuum to the distributor's vacuum advance (VA). The technical difference is whether the horizontal slit is located, above or below the butterflies (at idle); ported is above, and un-ported is below.

      I said un-ported since, though I have not ran a OEM carb for decades, I recalled well, when unplugging the VA hose from the carb nipple, there was a strong vacuum leak. That leak, if not plugged quickly (i.e. finger over it) would result in idle speedup a few hundred RPMs initially, then stumbling. If plugged, the RPM would drop down so slow it would seem about to die.

      Others said ported, and recalled none of the above; said nothing changed whether the VA hose was connected or not.

      I don't trust anyone's memory, esp. my own, so I looked at an old WCFB, which appeared to be non-ported. Several others ignored that observation, and suggested other ways to determine. Then we all took our marbles and went home. Later, a demi-god spoke.

      This morning, I looked very, very, very closely at the 1956 WCFB again, also a 1970s AFB, a 1980s Holley, and new Edlebrock. I used a scribe to trace the closed butterfly position, in relation to the vacuum slit. I also used a strong pen-lite to see down inside the venturi.

      After looking at the carbs, then refreshing my memory on "timed vacuum" in a 1980s Holley manual I'd had for years, I now have a possible explanation for the above: There is ported vacuum, and there is ported vacuum.

      The WCFB's slit is even with the butterfly, BUT the edge of the butterfly is angled upward & away from the slit, so the lower edge is effectively all that is below the slit. So technically, it is PORTED. The AFB slit is maybe 1/64" above where the WCFB's is, in relation to the butterfly, so it too is PORTED. The Edlebrock & Holley's slits are near 1/16" above the butterfly, so definitely PORTED.

      The difference is in timing; how far off idle, before the slits become un-ported. For the WCFB or AFB to stay ported, they must idle very slow, say around 550-600 RPM. Much above that and they become un-ported. The Edlebrock & Holley would probably still be ported at anything less than around 1200 RPM. Further, the OEM carb's transition to un-ported is likely much quicker due to the position of the butterfly, in relation to the slit when it passes it.

      The 59-64 Shop Manual says time the V8s at 600 RPM then readjust the idle to 550. That accounts for the different memories. I have set my Studes to idle at 750-800 is cool weather, and 850-900 in AC weather for as long as I can recall. At those idle speeds, the vacuum exists as I recall above. But for others, who set their idle around 550, there is likely little or no vacuum, as y'all recall.

      However, in light of the above, I MUST CONCEDE, technically speaking, all Stude carbs appear to be PORTED. (Though I am unsure whether a 56J with WCFB will idle with the butterflies locked in the bores.)


      I read this with interest. Thanks!

      Comment


      • #4
        So do I; Don't worry about hijacking my thread Joe. I found it very interesting. I'm just getting back into Studebakering after 40 years. The GT Hawk is my all time favorite car. I finally got another one. I enjoy reading these discussions.

        I looked at the old AFB that the Edelbrock replaced. I see what you mean about the slit in relationship to the throttle plates. I can see how you all came to different conclusions. I guess I'll do a little experimenting with the two vacuum ports, on the Edelbrock, once I get the VA repaired. I'm still not sure which one to use.
        1964 Gran turismo Hawk
        1954 Packard Pacific

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        • #5
          Thanks, Joe. I figured there must be a good reason the group was somewhat split on this.
          Dick Steinkamp
          Bellingham, WA

          Comment


          • #6
            Originally posted by erik64 View Post
            So do I; Don't worry about hijacking my thread Joe. I found it very interesting. I'm just getting back into Studebakering after 40 years. The GT Hawk is my all time favorite car. I finally got another one. I enjoy reading these discussions.

            I looked at the old AFB that the Edelbrock replaced. I see what you mean about the slit in relationship to the throttle plates. I can see how you all came to different conclusions. I guess I'll do a little experimenting with the two vacuum ports, on the Edelbrock, once I get the VA repaired. I'm still not sure which one to use.
            I have absolutely no qualifications to get into this discussion but I can tell you the vacuum line to the distributor on my Edelbrock is hooked to the far left port...(passenger side) and seems to work okay.

            Comment


            • #7
              Originally posted by E. Davis View Post
              I have absolutely no qualifications to get into this discussion but I can tell you the vacuum line to the distributor on my Edelbrock is hooked to the far left port...(passenger side) and seems to work okay.
              If I remember this correctly, and that's questionable any more, this would be "ported" and the one on the driver side would be "Manifold".

              Ted

              Comment


              • #8
                Originally posted by Chicken Hawk View Post
                If I remember this correctly, and that's questionable any more, this would be "ported" and the one on the driver side would be "Manifold".

                Ted
                Your memory seems sharper than ever Ted. It matches the 1406 Edlebrock out in the garage here. I did not trust my memory for a second, so went out to check. Its easy enough to pick a carb up off the bench and turn it over, but I would not go to the trouble of removing it from a car to have a look-see.

                Comment


                • #9
                  Originally posted by Chicken Hawk View Post
                  If I remember this correctly, and that's questionable any more, this would be "ported" and the one on the driver side would be "Manifold".

                  Ted
                  Correct..

                  If you notice the one on the Passenger side is higher than the one on the Driver side.

                  Thus the one on the Passenger side is above the throttle plate and is the Ported one.

                  Ported = Timed!

                  Which is the same as the original Carter AFB's location and functionality so we don't have to remember (age i guess)..
                  Last edited by SScopelli; 08-06-2013, 03:53 PM.

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