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are all q-jets the same?

Discussion in 'The Garage' started by 84gmcjimmy, Mar 5, 2005.

  1. 84gmcjimmy

    84gmcjimmy 1 ton status

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    are all Qjets with the same CFM rating, for the same kind of engine, the same? Excluding the computerized and new ones?
    I want to call LORDCO to see if they even have a q-jet rebuild kit. and i'm just awating a carb from James (79stomper) other wise I'd know.
    anyone know if the parts are interchangeable? and if the rebiuld kits are the same?
    What should come in the rebuild kit? Any special tools I need? Do I need one of those stands they advertise on JEGS, or shuld I be fine if I support it by little slices of wood?

    Thanks!
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    Depends what you consider the same. If you mean a federal emissions Monte Carlo SS from 1985 (as a for instance, US model) then yes, each one of those carbs is the same.

    However, if you got a 1985 Monte LS with 305 (not even sure if that was available, you get the picture though) then no, they aren't *exactly* the same.

    Getting out of the realm of CCC so I can clarify what you are asking, if you got a 1977 truck with emissions class (same engine size) that didn't require EGR, and you had another 1977 truck with the same setup, except it required EGR, the primary jetting, along with other things would be different. High altitude, Federal vs. California emissions, then of course the respective engines, transmissions, etc. All compensated with by things like float level, primary rods/jets, secondary rods/hangar, power piston spring, and so on.

    It sounds like a lot, but the only things I've ACTUALLY noticed when bolting X carb on Y motor, is that using an EGR carb on a non-EGR application will be noticed, and putting a carb from a much smaller engine may result in fuel starvation on a larger engine.

    To get perfect tune as GM did though, requires a lot of tweaking, etc., which if not adjusted on YOUR vehicle, won't be "ideal", again as GM tested them.

    Each carb was built/calibrated/tested on each individual drivetrain offered that year.

    For parts, many things interchange as long as you stay away from non-CCC. But the primary rods/hangars changed at some point IIRC, and the carb bodies themselves changed about 1975, although both styles of body were used later than that date. Choke varied based on year as well, some can be changed by simply unbolting and swapping, other castings aren't as adaptive.
     
  3. big83chevy4x4

    big83chevy4x4 3/4 ton status

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    both q jets from my 83 k10 and 83 k20 were WAY differnent. you need the numbers off the side to get the correct kit. there are a few parts that interchange, but not many.
     
  4. 84gmcjimmy

    84gmcjimmy 1 ton status

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    yikes! I think I will wait until I have both carbs beside each other then I will find out.
    Are there appearence the same with the EGR compared to the non EGR? Or if I had 2 different ones, would I beable to tell?

    Thanks.
     
  5. 84gmcjimmy

    84gmcjimmy 1 ton status

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    okay I will wait until I get the carb to order the kit.
    Thanks for telling me that!!

     
  6. dyeager535

    dyeager535 1 ton status Premium Member

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    No appearance diff EGR vs non-EGR, just in the primary jetting/rods.
     
  7. 84gmcjimmy

    84gmcjimmy 1 ton status

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    okay. I guess, like i said, I will wait until I have both then find out.
    Thanks!!
     
  8. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    Not all Q-Jets are the same!

    I remember reading about it in the "Rochester Carb" bible....you HAVE to check your casting numbers on the carb.

    The jets and other items will "appear" to be the same for all models but they are NOT interchangeable....

    I did some quick searching but can't find the details....yet.


    .
     
  9. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    Got it....here you go....

    "Rochester Carburetors" by Doug Roe c.1981
    p. 43-44


    "In 1975, rigid emissions standards...forced changes to idle, off-idle and main metering control...These units were first used on passenger cars and over the next six years, were fitted to trucks and commercial vehicles. These carburetors can be identified by the distinctive shape of their air horn and the beginning digit of their part numbers -- 1 (one).

    The primary metering rods with a "170" prefix part number are 0.080-in shorter, and theri part-throttle metering area - including tapers to the power-tip area -- is quite different from pre-'75 designs.

    The rods are NOT interchangeable. The part number range of these primary rods is 17051336--52."






    .
     
  10. Z3PR

    Z3PR Banned

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    Hey, I had a 1985 Monte Carlo CL. It had the 4.3 V6 with TBI. Miss that car, it was a nice driver.
     
  11. 84gmcjimmy

    84gmcjimmy 1 ton status

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    Greg,
    thanks, sometimes im such an idiot. jiminycricket on this board lent me that book to use when I rebuild it.
    I have a hard time reading books because I have a hard time focusing, and I can't really understand some things, thanks I will look at it in a few mintes.
     
  12. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    No problemo....

    It feels good to know an answer once in a while. I've had plenty of CK5'ers jump in and save me just before I was about to do something wrong, or spend money on the wrong parts to resolve an issue.

    .
     
  13. R72K5

    R72K5 Banned

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    theres billion different castings, its a mess, then theres 701 series 702 series, 703 series 704 series 1705 series 1708 series, and others, minor changes alot of times, just enough ot change gasket a little bit

    and etc..

    minor changes soemtimes and other times major changes

    cfm on qjets were 800 and 850

    way to tell physically is by looking at the size of the annular ring in the primaries, bigger ring is 800(more restrictive), smaller is 850(less restrictive)
     
  14. 84gmcjimmy

    84gmcjimmy 1 ton status

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    alright thanks Randy. Looks like I will have to really stare at them and llook up the casting numbers when I get the 2nd one. thanks
     
  15. dyeager535

    dyeager535 1 ton status Premium Member

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    It's 750 vs 795 (or 800CFM depending on what literature you read) CFM for factory Q-jets. Not that it matters much, just that the new Edelbrock Q-jets are the only 850's in existence.
     

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