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  1. #1
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    Default Daily mild 308 Carb choice

    I have a WB ute with a rebuilt 308 and 4 speed, no one can give much of a definitive answer and theres tonnes of different opinions on what is the best carby size I should use. Many have said to keep the Quadrajet, others say you cant go wrong with a Holley.

    I have also previously tried a FITECH EFI 400 W/Fuel command centre and had nothing but issues.

    Any suggestions would be welcome.

    Specs:

    308, dish pistons
    Old heads with port matching and 3 angle job
    ICE ignition system (adjustable)
    2.73 diff ratio (9 inch)
    M21 4 speed
    204/214 @0.050 cam
    Edelbrock performer manifold
    Factory style Quadrajet carb and 1/2 inch 4 hole spacer, charcoal canister and PCV hooked up and working
    Ceramic Pacemaker headers w/dual exhaust and lukey style mufflers

    It is my daily driver, mostly on 95 and I use AC every day due to my location being Darwin. I am after fuel economy and torque due to the diff ratio and AC.

    I have so far looked into:
    Keeping Quaddy
    Holley 350 W/adapter
    Holley 390 4 barrel
    Edelbrock AVS2 500
    Holley Sniper EFI

  2. #2
    been here .......too long Smitty2's Avatar
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    .. keep the Quaddie

    by design, it is better fuel economy wise but will still give you a kick
    when those secondarys open!
    plus
    all your hoses, accel cable connectors are all bolt on factory style
    as is the carb itself... spreadbore carb on a spreadbore manifold
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  3. #3
    Senior Member TonnerGuy's Avatar
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    Default

    Quaddy for sure, what was the problem with the Fitech ? have considered one on my 308.

  4. #4
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    QJ is probably best for your combo which is pretty mild looking at the cam.

    If you did want to change to another carb, the Edelbrock 650 AVS carb would be an excellent choice. The secondaries are adjustable on this carb, like the QJ. They are extreeeeeeemely reliable [ like the AFBs ] & will go for years without servicing & give good economy. Many people think the QJ, AVS & AFB are vacuum secondary carbs. Incorrect. They are mechanical secondary, all 4 barrels go to WOT when the #10 hits the gas pedal.

    Holleys make excellent paper weights....

  5. #5
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    If you’re sticking with spreadbore. Stick with a quadrajet. Or one of those edelbrock thingys.

  6. #6
    been here .......too long Smitty2's Avatar
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    Quote Originally Posted by GtoGeoff View Post
    QJ is probably best for your combo which is pretty mild looking at the cam.

    If you did want to change to another carb, the Edelbrock 650 AVS carb would be an excellent choice. The secondaries are adjustable on this carb, like the QJ. They are extreeeeeeemely reliable [ like the AFBs ] & will go for years without servicing & give good economy. Many people think the QJ, AVS & AFB are vacuum secondary carbs. Incorrect. They are mechanical secondary, all 4 barrels go to WOT when the #10 hits the gas pedal.

    Holleys make excellent paper weights....
    haha... Holleys make excellent paperweights ! never seen that before

    also a correction, Quaddies have a vacuum operated secondary system
    The throttle blades are mechanically connected to the throttle system
    but you get nothing, no action unless the vacuum operated airvalves
    (aka THE Secondarys) open and fuel flows into the secondary openings
    in the main body courtesy of the secondary metering rods being lifted
    by the vacuum controlled airvalves and the vacuum drawing fuel from
    the carbs fuel wells which gets discharged from the secondary fuel nozzles

    It is important to note that the secondary airvalves only open as
    far as needed to supply the amount of air the engine needs as
    indicated by the amount of engine vacuum.

    So if the 4 throttle blades are open and the airvalves closed ...
    the engine is only getting the air/fuel it needs from the Quaddie's
    primary system. So you don't get full WOT until the vacuum operated
    airvalves open...
    Last edited by Smitty2; 04-01-2019 at 10:17 PM. Reason: spelling
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  7. #7
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    Hey Smitty. I have some primary and secondary metering rods from a blue 308. Is it worth trying to sell them? Or can you still get them new?

  8. #8
    been here .......too long Smitty2's Avatar
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    Quote Originally Posted by Castiron355 View Post
    Hey Smitty. I have some primary and secondary metering rods from a blue 308. Is it worth trying to sell them? Or can you still get them new?
    yeah... still available new
    several sources in Oz inc eBay, plenty of places in the USA
    even Amazon (as well as JEGS Summit) sell them
    ditto with the jets ...even all the different hangers

    https://www.ebay.com.au/itm/CARBURET...fkQW:rk:2:pf:0
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  9. #9
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    Sweet. Cheers.

  10. #10
    Not the Kingswood! hq308's Avatar
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    If you still have the Fitech re-fit but replace the command centre with a surge tank. The command centre is junk but the Fitech is pretty good when set up correctly.

  11. #11
    Do you ever leave? EH179's Avatar
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    Quote Originally Posted by GtoGeoff View Post
    QJ is probably best for your combo which is pretty mild looking at the cam.

    If you did want to change to another carb, the Edelbrock 650 AVS carb would be an excellent choice. The secondaries are adjustable on this carb, like the QJ. They are extreeeeeeemely reliable [ like the AFBs ] & will go for years without servicing & give good economy. Many people think the QJ, AVS & AFB are vacuum secondary carbs. Incorrect. They are mechanical secondary, all 4 barrels go to WOT when the #10 hits the gas pedal.

    Holleys make excellent paper weights....
    Haha... the BS meter rates high with this one...QJ are "mechanical secondaries"...really, lol.
    Why wont the sec' air flaps open in Park/Neutral when sinking the boot in, like Holley DP's do? lol
    Smitty explained why this is so...

    Holleys make excellent paper weights?... for all the refund dockets on the rubbish carbs that have been returned, perhaps.

  12. #12
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    Yes, EH179, they are mech sec carbs. Learn about how carbs work before you post.

    I suggest you try & find the original Holley Carb book, written by Holley engineer & future vice president, Mike Urich. On page 42 you will find this:

    " Mechanical secondary carbs are opened by a direct link from the primaries, usually on a progressive basis so the secondary opening is delayed until the primaries have reached approximately 40* of opening."
    This definition fits ALL Carter/Edel 4bbls carbs, QJs & TQs.

    As opposed to diaphragm operated secondaries. Page 43." These carburetors [diaph sec ] use a diaphragm to open the secondary throttles."

    Smitty2,

    The AFBs, AVS, QJ etc do use vacuum...sort of..... to open the air door. GM description of sec operation: " As air flow through the sec throttle bores creates a low pressure [vacuum] beneath the the air valve, atmospheric pressure on top of the air valve forces the air valve open against spring tension. AFBs & QJs have ingenious 'starter' or low speed ccts on the secondaries that get some early fuel flowing before full airflow is reached. This eliminates a bog.

    To the OP.

    If you have a single plane intake man, a 500 AVS would be ok. With a dual plane, a 650 would be better.

    Before Edel got into the carb business, they compared a Holley 600cfm 6619 carb against a Carter 625cfm carb on a 350 Chev. The Carter made 17 hp more, 17 ft/lbs more tq & used less fuel doing it....
    PM if you want a copy of the test.

  13. #13
    Do you ever leave? EH179's Avatar
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    [QUOTE=GtoGeoff;753335]Yes, EH179, they are mech sec carbs. Learn about how carbs work before you post.

    Idiot! Read what i said in second sentence of post # 11. They are "NOT MECHANICAL"...

  14. #14
    Sure why not? 76lxhatch's Avatar
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    You could argue either way because its a combination of both. Yes the main secondary throttle blades are mechanically operated by linkage, which is often the traditional meaning (especially when comparing to simple designs). However the secondary circuit requires vacuum to deliver fuel, so in that sense it is vacuum operated and you could probably argue that technically the air flap is also a throttle since it blocks air.

    The answer to the original question is to keep the Quadrajet, but don't forget that carbs don't magically tune themselves any more than EFI.

  15. #15
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    That’s Quaddies in nutshell really. No one knows WTF is going on! Hahaha!!

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