Small primaries and large primaries

Discussion in 'Troubleshooting & Diagnosis' started by JD Z, Oct 29, 2017.

  1. JD Z

    JD Z Veteran Member

    A family mechanic suggested I would want a carburetor with small primaries and large primaries. He is a fan of the quadrajet and worked on many in his day. His preference was Edelbrock and I haven’t looked into that carb yet. Fuel economy for cruising and fouled plugs was a theme for my situation in his mind.

    I’m looking to go to a 650 carb from the 750 Holley currently on the car. The local mechanic said it was too large for the car. No choke being one of the problems. Looking for suggestions on the primaries and brand to consider.
     
  2. Dave Nelson

    Dave Nelson Veteran Member Gold Member

    3,077
    332
    Dec 19, 2003
    Vineland N.J USA
    He is correct about the quadrajet, it is a excellent street carb.
     
  3. SRGN

    SRGN Veteran Member

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    Feb 20, 2009
    Central NJ
    Quadrajet is what the car was born with. 780 cfm.
     
  4. JD Z

    JD Z Veteran Member

    Thanks guys. Against the family mechanic’s recommendation, I ordered a Holley 83670 - 670cfm carb. Electric choke which is needed. An 80670 was recommended from the shop and Holley suggested aluminum for better management of heat under the hood.

    I look forward to driving with this new carb and a professional tune.

    I remember the sound back in the 80s when that quadrajet kicked in. It was a sound and feel to remember. Driveability and kick in town 0-45 is important. 0-70 as well. We will see how this Holley stacks up against my memory of old and the current 750cfm Holley. :)
     
  5. FlaJunkie

    FlaJunkie Veteran Member Lifetime Gold Member

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    Mar 24, 2001
    Rockledge, Florida
    I am totally lost on this thread...
     
  6. JD Z

    JD Z Veteran Member

    FlaJunkie, if your lost the key point is:

    “I’m looking to go to a 650 carb from the 750 Holley currently on the car. The local mechanic said it was too large for the car. No choke being one of the problems”

    The primary question was to gain insight on the quadrajet or others with a small/large primary. Yep, I didn’t go Edelbrock or Quadrajet. Many insight points beyond what we see. Sharing where I landed for chance it may be useful in some way shape or form. No more questions for me on this thread.

    I kindly shared where I landed.
     
  7. FlaJunkie

    FlaJunkie Veteran Member Lifetime Gold Member

    5,685
    37
    Mar 24, 2001
    Rockledge, Florida
    If you have a high performance V8, max air flow is about 800 cfm. The 'mechanic' would only be right if you have an average reving motor.
     
    JD Z likes this.
  8. '71StreetZ

    '71StreetZ New Member

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    Aug 18, 2017
    I have always heard that you can calculate needed CFM with a simple equation
    ( CFM = Displacement (Cubic Inches) x Desired RPM / 3,456 )
    An average 350 at 6k rpm would be 350 x 6,000 / 3,456 = 607.638
    so a 650-670 carb should be plenty
     
    JD Z likes this.
  9. 80sz

    80sz Veteran Member

    2,154
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    Feb 2, 2014
    Buffalo,n.y.
    You will be fine with the carb. I liked the old wawoomp style of the quadrajet also,it just sounds cool!
     
    JD Z likes this.
  10. JD Z

    JD Z Veteran Member

    80sz, yes I remember the wawooomp. Liked it.
     

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