Dual Quads or Single Carb?

Discussion in 'Engine Topic' started by Patsfan54cc, Jan 5, 2015.

  1. Patsfan54cc

    Patsfan54cc New Member

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    I just picked up a 5.7 crate motor w/vortec heads all stock. I have a TH350 & 3.08 gears. I'm changing this over to a carb but my son-in-law & I are in a bit of a disagreement. I do plan on putting a cam in it (nothing to radical) & I want dual quads but he say's it will be a dog. He says go with a single Demon 750. Who wants to break the tie? Also any suggestions on a cam? Thanks
     
  2. kimosabi

    kimosabi Veteran Member

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    Add here's why it would probably be a dog, as your son in law says:

    Your stock 350 will need at most 550cfm of air at 6000rpm. Give or take a little.

    Smallest quad I could find on Summit is a 600cfm carb. Which means that even though you find two 500cfm quad you're not giving it any throat at all, doubling capacity to 1000cfm, which will really hurt/slow down your intake charge as well as reducing carb signal. No stock engine with stock compression is gonna like that.

    You need some vacum and carb signal for it to operate at its moste efficient.

    Stock Vortec heads are said to have a lift limit of about 0.450.
     
  3. Rockhound

    Rockhound Veteran Member

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  4. 351maverick

    351maverick Veteran Member

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    I'd run a single 4 barrel on a tunnel ram for the badass factor before dual quads on a flat manifold
     
  5. B2inSC

    B2inSC Veteran Member

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    I cant think of any practical street application where more than one 4bbl carb would be required or would run well.

    Even the factory tri power cars ran off two barrel primary with vac actuated secondary carbs.

    No way I'd put multiple carbs on a stock motor...or even significantly modified one.
     
  6. hogg

    hogg Veteran Member

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    i ran two 4's ,500 ,on a stock 73 350 with old 64 cc heads ,. Ran very smoth and idel very good . had progressive lenkage,ran on two barrals most of the time with what ever leked past the others. Didnt like being put to the floor at full stop but would still go and was a lot of fun at say 40 or 50. The car only had a 273 rear. A single carb wood have been faster . BUT HAD A LOT MORE TO TALk ABOUT WHEN I OPENED THE HOOD. Old school
     
  7. APEowner

    APEowner Veteran Member

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    You can get dual quad setups to run well on the street but it's cost more and require more fiddling than just bolting on a single 4brl so from a practical standpoint the single carb is the way to go. However, we're not talking about building a practical car. We're talking about something that makes you feel good when you're driving it and/or showing it off. If you like the idea of dual quads and have the resources to go that way then go for it. It'll run just fine and have quite the wow factor when you pop the hood.
     
  8. 1980RS

    1980RS Veteran Member

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    I can tell you from experience that the 750 Demon is going to be way too big, the dual fours with 500 will not be a dog as I had that setup on my kids Vortec 350 but there is a lot of fiddling around with them as both carbs with idle curcuits are hard to balance out. I am surprised that Eddy does not sell one with out an adjustable idle the way GM and Chrysler did it.

    I can also tell you that a 600 Eddy 1405 with a little work goes great on the Vortec engine, mine has the LT4 Hot Cam and I am very happy with it, if you decide to get a Demon go with the smaller one it will work better.
     
  9. rtanner

    rtanner Veteran Member

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    dual quads, gasoline will be 1.50 gallon by march 2015
     
  10. ddeennis

    ddeennis Veteran Member

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    I read the same stuff each time this subject comes up and most of the
    information given about two carbs is false and totally not true, many folks that give advice about dual fours on the street never owned a tunnel ram and only pass on what they heard from another who had issues, they had issues cause they had no clue on how to set up the carbs and final tune to timing and such.

    So here we go, you have to fiddle with them, they don't work, carbs are hard to tune, too much cfm, weak throttle response and so on, just not so. really have no merit to any of it.

    So you want the truth, you ignore the folks who say it can't be done and say it don't work and it's just full of fiddling. Because they are just passing on what they was told.

    Then you ignore the folks who say the tunnel ram wil run like a dog, because they didn't own.

    The ones who says your car will run better with a single carb vs dual carb
    has some merit, not all cases, you will find increased torque and power with a tunnel ram and dual 4's in more then just a few cars.

    It comes down to knowledge and your ability's.

    Look, I took a single carb off my car and stuck on a tunnel ram with 2 600 vacuum secondary carbs, I went faster and quicker down the 1/4 mile, then I switch to two 750 VS and still went faster and quicker yet, I picked up low end power and mid range torque, I ran that combo for about 2 years or better and never once had to adjust the carbs- never!

    Then I built a 6-71 blower off a firetruck to put on my car and transfered the carbs from the tunnel ram to the blower, for two years now I have not had to touch the carbs, never even pulled off the air cleaners.

    If I had listen to the crap advise most give on this subject I would have never
    done a tunnel ram or built my own blower ( which I know is another subject), I will tell you OP first hand you can run two holley 600 vs carbs with great ease specially if you used a tall tunnel ram, you would pick up velocity and increase power in the lower end, using a short style dual intake you will give up some power down low but it's not the end of the world kinda power


    You have to be aggressive with your timing you going to have to crank in all the initial timing the engine will take and shorten up the mechanical advance and make it come in quicker around 2500 rpms.

    So timing is important you should get a head start on that before a swap and crank up the timing. So that way when you set the intake on with two carbs you can work on only carbs cause your dist will be ready to go ,timing is done for the most part.

    using two 600 vs holleys you would only run on the primary's with a 1 to 1 throttle linkage- like the cheap 15 dollar units summit racing sells and what I used, it would be the same as a double pumper with 1 to 1 linkage and nobody &itches about a 600 holley double pumper sitting on a 350 sbc engine do they? So thats how the car will respond, then the secondary's can be adjusted with a spring whether black, purple or white til you have a smooth transition to all eight barrels.

    Look my father in law runs around with a stock 350 sbc with mild cam and a tall tunnel ram with two 750 eddy carbs and he built that thing like 3 years ago, I set up the carbs the same, got all the throttle blades set the same and tied the two carbs together with 1 to 1 linkage, adjusted the idle mixture screws and off he went, I already had the dist dialed in so it was just a matter of making the two carbs the same in every way. he even runs around with a 2 something rear end gear and 4 speed tranny, so he lugs that thing at times but it don't die he just gives it alittle more gas and off he goes with a grin on the face.

    Friend of mine same deal with his Nova sbc 350 tunnel ram with two 750 carbs granted he has some 3.73 gears little stall in street trim turns 12.50-.80
    with that little light Nova

    Just make sure both carbs are the same in every aspect, float level, throttle blade angles everything and anything you can think of, they both be the same and make sure you crank up the timing.

    here's a few pic

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    Last edited: Jan 7, 2015

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