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Q-Jet vs. A.F.B.

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by 85Blazernga, Apr 23, 2001.

  1. 85Blazernga

    85Blazernga Registered Member

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    Can anyone explain why a Q-jet is better at handling angles and hills off road than an A.F.B.?

    I am in the process of replacing my 5.POS with a 350. I am replacing my old carb for a refurbished Edlebrock. I know that the A.F.B. will give me better performance on the street but I don't think I want to sacrifice any off roading characteristics. Any help is appreciated.

    GSB
    Forever #3!!
     
  2. my old edlebock would spudder and die if i had one wheel on a curb! you won't be happy offroad. Q-jets have better float boals- centrally located. my q-jet handls all but the steepest inclines.

    78, 350/350/203, 3/4 ton, 4" lift, 35" BFGs[​IMG]
    <A target="_blank" HREF=http://bluebeast.coloradok5.com/>http://bluebeast.coloradok5.com/</A>
     
  3. Blue85

    Blue85 Troll Premium Member

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    The Q-Jet rules at the tippy angles because the fuel bowl is in the middle, between all four of the barrells and is designed with the inlets and outlets in the right locations. Q-Jets have CFM ratings as high as any reasonable aftermarket carb due to the huge secondaries. The difference in size between the primaries and secondaries is the biggest reason that the Q-Jet can give you better gas mileage and still flow enough air for a big block. An A.F.B. or Holley may give better mid to high rpm power, but the difference will be small. The Q-Jet will give a better idle and better low rpm meaning that you will be able to lug the engine vs. just stalling it. Then at big angles the difference is night and day: the Q-Jet will run the engine and the A.F.B. won't.

    The only substitute for a Quadrajet on a 4x4 is EFI.

    <font color=green>"MAN THOUGHT HURT BUT SLIGHTLY DEAD" --Providence (R.I.) Journal</font color=green>
     
  4. LittlePig

    LittlePig 1/2 ton status

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  5. 85Blazernga

    85Blazernga Registered Member

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    Do you like the Edelbrock refurbished Q-jets? Heard that they could pretty much be bolted on right out of the box.

    GSB
    Forever #3!!
     
  6. Emmettology 101

    Emmettology 101 3/4 ton status

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    Those are nice but Pricey! Around $350-400.. I usually get the Auto Zone Rebuilt units for around $100-$170.... They also come with a 1 year warranty......

    Mike - <A target="_blank" HREF=http://emmett.coloradok5.com>http://emmett.coloradok5.com</A>[​IMG]
     
  7. 86blazerk5

    86blazerk5 1/2 ton status

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    I have been wondering this my self lately and was just about to make a post about it and I saw this one. If I spent big money and replaced my old q-jet with a nice new 420 dollar edelbrok q-jet, Would I notice a difference over replacing it with an under 200 rebuilt Q-jet?
    Ike

    Spreading The K5 Gospel!
     
  8. Emmettology 101

    Emmettology 101 3/4 ton status

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    Not sure, cant help ya there. I have only ran the chepo units from Auto Zone. However, if my budget could afford one, I would probably buy an Edelbrock unit or one from Jet....

    Mike - <A target="_blank" HREF=http://emmett.coloradok5.com>http://emmett.coloradok5.com</A>[​IMG]
     
  9. Blue85

    Blue85 Troll Premium Member

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    Well diesels use injection, so yeah.

    <font color=green>"MAN THOUGHT HURT BUT SLIGHTLY DEAD" --Providence (R.I.) Journal</font color=green>
     
  10. Twiz

    Twiz 1/2 ton status

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    I'm trying to do a custom cut, rebuilt q-jet flow bench test and M.P.G. test soon. I have one normal rebuilt q-jet and a modified one and plan on testing them both. I hope the results are worth the effort. I'll make a post when I get it done. Should be cool (I hope) I'll still make a post if it doesn't do what i thnk it should. Keep an eye out for it.

    In a nut shell.
    I'am focusing on primary signal and atomization by maximizing the "mass production, as cast q-jet assembly". That should icrease eonomy and off-road capibility. I plan on also checking the fuel dilivery on angles. I'm in the process of putting togather a visual flow bench with maomeaters. Any in put?

    This is something I've wanted to do for awhile, but it's always been on the back-burner.

    Needless to say I'm sold on Q-jets for off road. (next best thing to T.B.I., T.P.I, o rdiesels ( clackers)

    Twiztid
     
  11. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    I'm quite interested Twiztid...please keep us all informed as to the progress of your testing. Better performance is a shared goal...I personally hate the flooding probs on bad angles with my AFB clone! It tends to take the fun out of a steep rocky hill[​IMG]

    I'm thinking of going the Q-junk reman route and maybe incorporating some of your mods if the testing looks good.

    Rene

    [​IMG]<A target="_blank" HREF=http://jules.coloradok5.com>http://jules.coloradok5.com</A>
     
  12. dyeager535

    dyeager535 1 ton status Premium Member

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    Are you going to be "knife edging" and reducing the cross section of the choke blade and primary throttles? Check out the idle bleeds(?) because as the Q-jet got older, the size was reduced, decreasing the ability to use radical cams and still modify idle mix accurately.

    Dorian
    My K5 and Chev/Olds tech/links page: <A target="_blank" HREF=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</A>
     
  13. Twiz

    Twiz 1/2 ton status

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    dyeager535

    My modified Q-jet is a 17058213 (as per your web page a 1978) It has the air bleads/emulsion tubes the jet out into that primary booster. Not the more typical bleads that are streight up (pre 76 I think) I chose this carb for my guinny pig for the emulsion tube, I'm shooting for max atimization.. --allthow all of these mods will appliy to all q-jets-- except maybe the 'letric ones. I will modify a pre '76 carb if this one turns out O.K.

    As far as getting around the idle problem with a lumpy cam. I will drill a small hole the primary throttle blades, to feed the engine more air, if need be.That should get the idle fuel adj screws back in line. I have done this and it works. Allthow, I am not useing a very raidcal
    (218 @ .050 int. and 226 @ .050 ex. .462 int lift .480 ex. lift)

    As far as the modifications. Basicly, just cleaning up the as cast Imerfections, turning the carb back into what the designers had probably origanly intended. Cleaning up the air flow path to the boosters and venturi, and knife edgeing the throttle blades, I eliminated the choke and am useing it elsewhere (I have never had a properly working choke on anything I ever drove and have done just fine. I think chokes are one of those "for the majority" kind of things. Oddly enuff a Bic pen wedged between the gas and brake pedal seams to work just fine for me, but thats just me.)

    I was hopeing you were going to hitt this (dyeager), I can probably use your thoughts and ideas. Checking out your page, you are da-man to ask. Expect to see a P.M. from me as this sucker gets closer to being done.

    Thanks for your time

    Twiztid
     

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