Carb Sizing on Blower Motor
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Carb Sizing on Blower Motor

  1. #1
    Senior Member stewvette's Avatar
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    Default Carb Sizing on Blower Motor

    I was looking for a recommendation on sizing some carbs for my setup. I used an equation from the holley tech manual and it says i'm ok with two 750's but i see most people running big dominators on similar setups as mine. I hear that any restriction on the inlet side of a blower is bad but can you also go to big and make it hard to tune, and loose drive-ability? Right now i'm running two 750's and was wondering if there would be an advantage going larger like some 4150 950, or should i get dominators and what size? Right now I have a 6-71 mike kuhl i'm spinning 10 over to get 5lbs of boost, im swithcing to a 10-71 Bds this week. This is a lake hot rod not a max effort by any means. Its in a 21 Daytona Jet.

    Chevy Gen 6
    540 4.25 stroke 8.1-1 cr
    AFR 325 heads
    dont have cam specs with me but around 255 at .050 613lift 114 sep
    BDS 10-71
    superchiller
    spinning 6 to 6300 rpm
    looking for 7 lbs boost on new setup
    running pump gas
    Last edited by stewvette; 08-06-2012 at 04:53 PM.

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    gn7
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    You're right there. I perfer to run a little bigger than the formula I use comes up with, but if you can hit the boost number you're looking for and turn the RPM you're shooting for, I wouldn't change it. I'd run what you have and seen if you get the numbers you're looking to get.
    There is no power difference between 7lbs with a 750 and 7lbs with a dominator.

    If you decide you want larger carbs, I wouldn't go over 850s. You definitely don't need dominators.

    I know that Holley doesn't sell a 850 blower carb any longer. But the 950 actually flows slightly less air than the 850 and will work fine on you deal if you decide you want to go to a larger carb.



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    Last edited by gn7; 08-06-2012 at 05:20 PM.

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    Second Chance unpredictable27's Avatar
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    I pretty much have the same set up but only turning a 8-71. Have demon 850's put bigger jets in um but it's on the boarder or to much fuel and the exhaust runs pretty hot. Not sure if there's to much Cfms or what. I'd probly go with 750's and a couple sizes up on the jets.

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    Senior Member stewvette's Avatar
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    Quote Originally Posted by gn7 View Post
    You're right there. I perfer to run a little bigger than the formula I use comes up with, but if you can hit the boost number you're looking for and turn the RPM you're shooting for, I wouldn't change it. I'd run what you have and seen if you get the numbers you're looking to get.
    There is no power difference between 7lbs with a 750 and 7lbs with a dominator.

    Ok that's what i was thinking thanks for the insight gn7. Would it work if i put a vacuum gauge on the base plate and see if there is some sort of reading there at wot? Have you tried this? I would hate to be spinning the blower faster than needed to get the boost number i wanted because i have a restriction on the inlet. But i'm all for not buying things that aren't needed, much rather test first than just buy and bolt on hoping for results.

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    gn7
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    Quote Originally Posted by unpredictable27 View Post
    I pretty much have the same set up but only turning a 8-71. Have demon 850's put bigger jets in um but it's on the boarder or to much fuel and the exhaust runs pretty hot. Not sure if there's to much Cfms or what. I'd probly go with 750's and a couple sizes up on the jets.
    No there is not too much CFMs.
    Hot exhaust is caused more by retarded timing than fuel unless your really dumping too much, which I doubt. There is no reason a pair of 850s won't work just fine on your deal.

    If your timing is too retarded you could be killing your exhaust valves. If your running dry exhaust your killing your headers as well.



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    gn7
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    Quote Originally Posted by stewvette View Post
    Ok that's what i was thinking thanks for the insight gn7. Would it work if i put a vacuum gauge on the base plate and see if there is some sort of reading there at wot? Have you tried this? I would hate to be spinning the blower faster than needed to get the boost number i wanted because i have a restriction on the inlet. But i'm all for not buying things that aren't needed, much rather test first than just buy and bolt on hoping for results.
    Depending on the blower itself, and how its set up, as in no stripping, and you can hit 7 lbs of boost with something in the neighborhood between 5% under and 1 to 1, I wouldn't worry about it. My guess is it will be closer to 5% under.



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