carb size on roots blower
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carb size on roots blower

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    Senior Member APOLLO's Avatar
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    Default carb size on roots blower

    What will a motor do on the dyno that is using a roots blower with small carbs? I was using the formula from BDS to see what CFM will be needed with the boost being used. I'm thinking is it will tip over on the dyno. Run out of air being pulled through the carbs. Hope I'm asking this right!! Not sure what it will do. Thanks

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    gn7
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    A little too small may not hurt max power as much as you think. In actual use it will hurt acceleration more than top speed unless they are stupid small. A roots will pull air thru a carb better than you might think. But if they are too small, you may see them go rich at higher Rs. Not from lack air flow, but the extreme pressure drop will go outside the carb's calibrations.
    Blowers do like their air flow.



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    Senior Member dankdave79's Avatar
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    What size carbs would u put on a 565 with a 14-71

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    Saw a 540 10-71 deal at a local shop...3- 850's

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    For instance. On my 525 bbc have two 750's. I put about 4 to 6 pounds of boost to it and the dyno showed it was pulling like 1300 and something of cfm. Can't seem to find the sheet but I believe it was something like that. Probable wrong with that number but I'll use that as a example. If it was 1300, Than that means I have 200 cfm left on the table. If I spin the blower any harder it will go past the cfm that is left on the table. This is where is was wondering what will happen. I say on the dyno is because I can see it I guess.

    Formula being used is this. [(DXR)/3456]X[(B/14.7)+1] = C

    D=cubic inch displacement of the motor
    R=maximum engine RPM
    B=maximum blower boost
    C=maximum CFM required

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    Senior Member APOLLO's Avatar
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    Quote Originally Posted by SoldHondaBoughtHondo View Post
    Saw a 540 10-71 deal at a local shop...3- 850's

    Willing to bet he had three carbs just for the wow factor!

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    gn7
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    You need to know the engine size, rpm, and the desired boost. Blower size is not all that important.



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    Last edited by gn7; 03-02-2014 at 06:12 AM.

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    Quote Originally Posted by APOLLO View Post
    Willing to bet he had three carbs just for the wow factor!
    Don Hampton has been selling a tri carb adaptor since before the dominator was available



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    With a roots blower, I would rather ''error'' to the large size with carbs. On a N/A street engine, i would rather error to the small side.

    Its pretty hard to overcarb a roots, within reason. I had a little 250 B&M with a single 1050 carb. Switching to a pair of twin 850's on top, netted a little power increase, even though, it was way more carb than the engine required.

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    Senior Member SoldHondaBoughtHondo's Avatar
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    Quote Originally Posted by APOLLO View Post
    Willing to bet he had three carbs just for the wow factor!
    Gary Kincaid builds nothing just for the wow factor


    Quote Originally Posted by Mild Thunder View Post
    With a roots blower, I would rather ''error'' to the large size with carbs. On a N/A street engine, i would rather error to the small side.

    Its pretty hard to overcarb a roots, within reason. I had a little 250 B&M with a single 1050 carb. Switching to a pair of twin 850's on top, netted a little power increase, even though, it was way more carb than the engine required.
    I used to work for a guy who had a 350 in a mini truck. 6-71 @ 1:1 and 2 1050's (Rick King) Truck ran perfect, idled @ 1k if it was stone cold or up to temp and got 16mpg....But then again RK puts 660's on a blown bb and it ran pretty good to. Hows about an m-62 eaton on a 1100 cc motorcycle motor....with a q-jet. Motorcycle motors are over carbed even without boost.
    Basic old school 2 valve inline 4 will have the bore of the carb pretty close to the diameter of the intake valve.
    Last edited by SoldHondaBoughtHondo; 03-02-2014 at 07:48 AM.

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    gn7
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    Quote Originally Posted by SoldHondaBoughtHondo View Post
    Gary Kincaid builds nothing just for the wow factor
    Last time I saw that engine it was in a Hallett Vector.
    Today, 3-850s is a wow factor.



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    565 spinning 6300-6400 8-9 pound range what would u run

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    Quote Originally Posted by APOLLO View Post
    Willing to bet he had three carbs just for the wow factor!

    I'm betting not .....

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    Quote Originally Posted by dankdave79 View Post
    565 spinning 6300-6400 8-9 pound range what would u run
    I don't know the answer but i'll ask, what size blower

    "Dark Sarcasm"
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    fast is the other half.
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