Cruise Seems Lean

Fuel and Air Systems

  1. Mattax

    Mattax Just the facts, ma'am FABO Gold Member

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    Chrysler used a useless technique because their engines were efficient at idle.
    Nobody else back then could figure out how to do that.
    Yep. That must be it.

    Sorry, there's no magic in using manifold vacuum. The magic is in lighting the mixture so pressure maxes out around 20 deg ATDC. Its pretty much as simple as that.
     
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    • 512Stroker

      512Stroker We are all here because we are not all there.

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      I love all the posts, great stuff.
      To port or not to port the vacuum advance really boils down to how much initial timing your engine can tolerate. Remembering that you will need to curve the mechanical advance match.
      I do run my current 340 setup, ported, initial timing @ 18*
      All in @ 2400 rpm 34* total
      Cruz speed timing with vacuum advance is 44*, I would like more but the vacuum advance is adjusted out to the max.
       
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      • 71GSSDemon

        71GSSDemon FABO Gold Member FABO Gold Member

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        All this reading of Shrinker's.....just fascinating. Need to take breaks to try and absorb even a fraction of what is being said. Read through all of "Carb Issues" today. WOW.
        Thank you
        Eric
         
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        • Mattax

          Mattax Just the facts, ma'am FABO Gold Member

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          Shrinker sure didn't spoon feed!
          Tuner's posts are in general easier to apply directly to whatever issue or setup is being worked on.
          Shrinker gets us thinking about what is happening and why. In the long run, that's really helpful. The fact he was willing to share what he was learning with the 4 gas and dyno, along with distilling or highlighting papers he'd read is just incredible. Tuner does some of that too, and because he's worked on such a variety of street cars and been in the business so long, and a great learner himself, he has priceless insight.
           
          Last edited: Jun 10, 2021
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          • Mattax

            Mattax Just the facts, ma'am FABO Gold Member

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            Just for the record.
            1965 Cheverolet L-78 with 4150 list 3124
            65l78_9_4cb76915662fccb81e408f6ad568bf5e10224fb9.jpg

            This appears to be an original 4150 Holley List 2818
            47682672d1319133625-numbers-for-an-original-holley-2818-choke-housing-2818rh3.jpg

            As shown in this diagram
            B-ENGINE-IGN-05-vacuum-advance-lines.gif
             
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            • 71GSSDemon

              71GSSDemon FABO Gold Member FABO Gold Member

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              So, for anyone with specific 660 holley carb experience, in the below picture (just a pic from Google), #1 is where my vacuum port nipple is. #2 is tapped but doesn't appear to go anywhere. One of my carbs has a plug screwed in, the other is empty. Does anyone know if there is both ported and manifold vacuum ports on these? or can #2 be opened up somehow to have ported vacuum?

              upload_2021-6-10_12-52-6.png
               
            • 512Stroker

              512Stroker We are all here because we are not all there.

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              #1 is a blank hole that holley did not drill and tap for an idle mixture screw
              #2 may have been for ported vacuum but I am not sure?
              Normally ported or timed vacuum are drilled in above the butterflies and non ported full manifold vacuum are drilled in below the butterflies.
               
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              • 71GSSDemon

                71GSSDemon FABO Gold Member FABO Gold Member

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                #1 is definitely drilled in both carbs and has a vacuum hose nipple screwed in mine (pic above was NOT my carb/s)

                #2 is tapped to a depth of ~ 0.5-0.625" but it appears is deadheaded at the end.

                These are my actual carbs.

                Resized952021061095143536.jpg

                Resized952021061095143546.jpg
                 
                Last edited: Jun 10, 2021
              • 71GSSDemon

                71GSSDemon FABO Gold Member FABO Gold Member

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                marked up..

                InkedResized952021061095143536_LI.jpg
                 
              • Mattax

                Mattax Just the facts, ma'am FABO Gold Member

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                This is the passage for the timing vacuum on your block. See if the passage is drilled through.
                upload_2021-6-10_16-37-2.png
                Then check the face of the main body opposite the white arrow. There should be a drilling there.
                Shoot some carb cleaner or blow some air through to see if it goes through.
                Holley's website says it should.
                Holley 0-4224 660 CFM Center Squirter Carburetor
                then click specs

                Good illustrations identifying all of the passages and basic concepts in Urich and Fisher. If you find a used copy cheap, I think its one of the better books to start with. It does have some self promotion but still good a reference. https://www.amazon.com/dp/0895864339/?tag=fabo03-20
                 
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                • 512Stroker

                  512Stroker We are all here because we are not all there.

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                  Well
                  #2 i am not sure but that looks to high up on the cab to be for timed vacuum, but I have wrong before
                  #1 I definitely the full manifold vacuum port. I hope you have not been running them uncapped as shown, that would cause a huge vacuum leak.
                   
                • 512Stroker

                  512Stroker We are all here because we are not all there.

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                  Interesting your carbs have no secondary metering block, cant say I have ever seen that before.
                  How the hell does that work?
                   
                • Mattax

                  Mattax Just the facts, ma'am FABO Gold Member

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                  They're Model 4160. Metering plate is sandwiched in there.

                  This one is originally from a list 3310-3
                  upload_2021-6-10_16-53-54.png

                  Fuel enters at the bottom where the larger drill bit is.
                  upload_2021-6-10_16-55-2.png
                   
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                  • 71GSSDemon

                    71GSSDemon FABO Gold Member FABO Gold Member

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                    The one port is uncapped in the front carb as that is where my vacuum advance is normally connected, but I have to replace that hose. The rear carb has that port capped.

                    As for metering block for the secondaries, these run metering plates like many do.
                     
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                    • 71GSSDemon

                      71GSSDemon FABO Gold Member FABO Gold Member

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                      I think they flow equivalent to #74 jets. Just not adjustable but I do believe QFT offers a plate modified for removable jets instead.
                       
                    • 512Stroker

                      512Stroker We are all here because we are not all there.

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                      That clear up one question, you are currently running full manifold vacuum to your vacuum advance.
                      With it disconnected and the port capped with is your initial timing?
                       
                    • Mattax

                      Mattax Just the facts, ma'am FABO Gold Member

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                      FWIW there has been long discussions on what plate numbers have what drilling.
                      Secondary metering plate vs Secondary Metering Block?
                      Mike and Tuner have a good discussion about how the plates work on page 3.
                       
                    • 71GSSDemon

                      71GSSDemon FABO Gold Member FABO Gold Member

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                      IIRC, it is 20 deg initial and 38 deg all in
                       
                    • 512Stroker

                      512Stroker We are all here because we are not all there.

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                      It's going to get higher than 20* when connect it to full manifold vacuum.
                      Are you sure your transition issue is not caused by to much initial timing?
                      Something is wrong
                       
                      Last edited: Jun 11, 2021
                    • Bewy

                      Bewy Well-Known Member

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                      Mattax,

                      Sorry your post #101 on vac adv is totally incorrect. Set any Chrysler 6 or V8 engine to the factory initial 6-12* timing. With the engine idling, turn the dist slowly to advance the timing. Idle rpm will increase [ more hp ] & vacuum will increase [ increased efficiency ]. To do this, one could use more init timing....or use vac adv connected to man vacuum to get the reqd amount of timing for best idle.
                      The exh dilution of the mixture at idle & low rpms [ even worse with increased cam duration, the rough idle ] requires more time to burn as efficiently as possible, & that includes Chrysler engines, & this is achieved by more timing at idle.
                       
                    • 71GSSDemon

                      71GSSDemon FABO Gold Member FABO Gold Member

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                      Question on this statement, and just a question. If initial timing with vacuum advance disconnected, is set at 18-20 (already well above factory settings) this additional timing is there. Then if connecting to ported vacuum, it is as set. If connected to manifold vacuum, it will be considerably higher but only until the throttle is opened - same as ported vacuum as it is equal to manifold vacuum once the throttle is open. So, with a more aggressive initial timing and the mechanical timing limited due to this, are we talking the same thing to some degree (pun intended)?@mattax your thoughts on this statement?
                       
                      Last edited: Jun 11, 2021
                    • Mattax

                      Mattax Just the facts, ma'am FABO Gold Member

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                      Been there. Done that.
                      A long time ago.
                      Some of us learned the hard way that test doesn't show what you think it shows.
                      Shrinker explained why.
                       
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                      • 71GSSDemon

                        71GSSDemon FABO Gold Member FABO Gold Member

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                        @Mattax your thoughts on my statement in #121? Am I way off base? From above to the comments about your timing theory being incorrect:

                        Question on this statement, and just a question. If initial timing with vacuum advance disconnected, is set at 18-20 (already well above factory settings) this additional timing is there. Then if connecting to ported vacuum, it is as set. If connected to manifold vacuum, it will be considerably higher but only until the throttle is opened - same as ported vacuum as it is equal to manifold vacuum once the throttle is open. So, with a more aggressive initial timing and the mechanical timing limited due to this, are we talking the same thing to some degree (pun intended)?
                         
                      • yellow rose

                        yellow rose Overnight Sensation FABO Gold Member

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                        Maybe you could post a link to Shrinker’s discussion on that just as a refresher. When the distributor has a decent curve in it, running manifold vacuum isn’t a good idea. And if you do use manifold vacuum and the engine is happier you then need to figure out why.
                         
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                        • Mattax

                          Mattax Just the facts, ma'am FABO Gold Member

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                          This is correct

                          To some degree yes if you look at it in the way you just did.
                          In general no, because its fixated on a belief that extremely early timing and lean burns produce power.

                          @yellowrose
                          Sorry, My post was referencing
                          Sorry your post #101 on vac adv is totally incorrect. Set any Chrysler 6 or V8 engine to the factory initial 6-12* timing. With the engine idling, turn the dist slowly to advance the timing. Idle rpm will increase [ more hp ] & vacuum will increase [ increased efficiency ].

                          @71GSSDemon mentioned he had read Shrinker's posts, in particular the paragraph from post #10. Bewy obviously chose not to, or did but choses to believe the current magazine writers are more knowledgable. The two big points from Shrinker in those two paragraphs is that early timing goes with lean burns and there has to be enough later burn to push the exhaust out. Elsewhere he explains why lean burns are foolish at idle, but the bottom line is they don't make power. Maybe I can dig that out later and post it up. Tests in neutral do not indictate power.

                          @71GSSDemon following upo on 512stroker's question. Remind us. Was the vacuum advance connected during this last drive? and if so where?
                           
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