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Carb CFM Solving

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by beefcake83, Oct 29, 2001.

  1. beefcake83

    beefcake83 1/2 ton status

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    Just wondering if it's possible to find out what CFM my Q-Jet is without disassembly? The number off it is 17083226. I went to a couple decoding sites and if their info is right, I have a '93 Rochester.

    Gary Graham
    '83 GMC Jimmy w/ '94 350 'Beefcake'
    Eielson AFB, Alaska
    Metallica & Mountain Dew
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  2. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    It's whatever CFM the motor can handle. Most of the cases are 795. However if you motor can only pull 400 then it becomes a 400CFM. They self adjust to the engine they are bolted. That's why the seconds have the spring loaded flap. It opens to the amount the engine is pulling. You could take that carb off your motor and put it on a bigbloc and it should run ok. Worse case it might need bigger main jets.
    If you had a Hogly you would want no bigger than a 500CFM on a 305 or 600 on 350. Hogly's just dump gas and open flaps with no regard to what the engine can handle.

    Women dig dents and flat paint!
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    Grim-Reaper
     
  3. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    The CFM rating can be figured out by measuring the diameter of the primary throttle plates. The Rochesters came in two sizes, the smaller uses 1 3/32" diameter primary throttle plates and the larger version is 1 7/32" primary plates.

    As Grimmy pointed out, actual flow is based on demand.

    Rene

    <font color=green>Dyslexics of the world...UNTIE!</font color=green>
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  4. J.R.

    J.R. Guest

    but then thats why with a holley you dont over carb. the advantage to a holley is better and faster air fuel delivery to the motor.. if you are going to be just put-n around then use a q-jet, if you want performance then go with a holley. if you know how to set them and take care of them they will always give you the best perfomance.

    BIG BLOCK MAN
    "MORE POWER"!!
     
  5. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    <blockquote><font class="small">In reply to:</font><hr>

    if you know how to set them and take care of them they will always give you the best perfomance

    <hr></blockquote>

    Maybe top end, straight line, not on a side hill, or bumpy performance. Bring yer Holley to Moab and see how far you get.[​IMG]
    I hated my old Holley...between the fuel boiling, crappy mileage and zero-good luck with it off road I am now using it as a wheel chock. That's just my experience though, I've never pretended to be a Holley tuning genius[​IMG] I'd consider one on a street car...

    Rene

    <font color=green>Dyslexics of the world...UNTIE!</font color=green>
    <a target="_blank" href=http://coloradok5.com/gallery/project_T2> tRusty pics...</a>
     
  6. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Must be as flat as Ohio in Iowa [​IMG]
    Holly's will nto run on the trails here (tellico) unless they are propane converted.

    Women dig dents and flat paint!
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    Grim-Reaper
     
  7. J.R.

    J.R. Guest

    my holley hasnt failed me yet, and i have had the truck where the bumper was almost 6inches from the ground at the start of the hill. and for bumps try going thru a corn field with 6-8 inches of row discing at 30-70 mph. the ride was so rough i had cuts on my body from where the seat belt got me. im not saying they are perfect, and to each there own. but it works for me so i use them.

    BIG BLOCK MAN
    "MORE POWER"!!
     

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