Jetting
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Jetting

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    Liquid Louie flatcrzy's Avatar
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    Default Jetting

    I have a Blown 6/71 Ron Grose 496 BBC 966HP that I just bought from Folsom Cali! I live in Idaho and will be running the boat at 3055' elevation, it has 2 Holley 830 blower carbs 4150 80509 2. It's set for sea level, what would be my base primary and secondary jets at this level? It's running 6lbs of boost .0020 valve lash (hot) solid lifters, 29 degrees timing? Any help would be much appreciated!

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    Senior Member wizbang's Avatar
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    .0020 lash or .020 lash ???????

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    Liquid Louie flatcrzy's Avatar
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    .020

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    Some guy obnoxious001's Avatar
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    Quote Originally Posted by flatcrzy View Post
    I have a Blown 6/71 Ron Grose 496 BBC 966HP that I just bought from Folsom Cali! I live in Idaho and will be running the boat at 3055' elevation, it has 2 Holley 830 blower carbs 4150 80509 2. It's set for sea level, what would be my base primary and secondary jets at this level? It's running 6lbs of boost .0020 valve lash (hot) solid lifters, 29 degrees timing? Any help would be much appreciated!
    It probably makes sense to check with Ron or Joey Grose and see what they recommend,, I think the norm is 1 jet size down per 2000 feet, so if everything was truly correct and set for sea level,, maybe drop all the jets one size only to start.

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    Liquid Louie flatcrzy's Avatar
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    Got it figured out! Got actual elevation to adjust for because it's differnt than the true elevation. Went from 94- 82 to 98-86 to start with we'll see how she runs from there!

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    Quote Originally Posted by flatcrzy View Post
    Got it figured out! Got actual elevation to adjust for because it's differnt than the true elevation. Went from 94- 82 to 98-86 to start with we'll see how she runs from there!
    Umm,, you should be jetting down for altitude,, not up?

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    Quote Originally Posted by flatcrzy View Post
    Got it figured out! Got actual elevation to adjust for because it's differnt than the true elevation. Went from 94- 82 to 98-86 to start with we'll see how she runs from there!
    Sure doesn't sound like you have it figured out.
    1 size DOWN is enough.

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    Liquid Louie flatcrzy's Avatar
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    Quote Originally Posted by obnoxious001 View Post
    Umm,, you should be jetting down for altitude,, not up?

    Wrote it wrong, went from 98 86 to 94 82

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    Some guy obnoxious001's Avatar
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    Quote Originally Posted by flatcrzy View Post
    Wrote it wrong, went from 98 86 to 94 82
    Quote Originally Posted by Fiat48 View Post
    Sure doesn't sound like you have it figured out.
    1 size DOWN is enough.
    Quote Originally Posted by obnoxious001 View Post
    I think the norm is 1 jet size down per 2000 feet, so if everything was truly correct and set for sea level,, maybe drop all the jets one size only to start.
    I agree with Fiat,, I would not drop 4 sizes, safer to take smaller steps than to hurt the thing, particularly since you came on looking for advice.

    I think Burley is a corrected altitude of just over 4000 feet,, and one of my comp jet guys drops 2 sizes for the Burley race.

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    Bear in mind a carb somewhat.....self compensates fuel delivery....in that the air passing through the carb...drags fuel out with it. Less air.....drags less fuel (to a degree).
    Not so with an injector.....which could care less about available air. It's just fuel pumping through holes.

    What you are doing frankly scares Hell out of me. Especially knowing holley jet sizes and their numbers.

    Last edited by Fiat48; 07-29-2010 at 09:45 PM.

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    Senior Member Jim W's Avatar
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    Quote Originally Posted by Fiat48 View Post
    Bear in mind a carb somewhat.....self compensates fuel delivery....in that the air passing through the carb...drags fuel out with it. Less air.....drags less fuel (to a degree).
    Not so with an injector.....which could care less about available air. It's just fuel pumping through holes.

    What you are doing frankly scares Hell out of me. Especially knowing holley jet sizes and their numbers.


    Bob,

    for accurate tuning, who's jets would you recommend???

    Jim
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    Holley jets are fine. You just have to be aware of the actual diameters.
    Look at 80,81 & 82. Those are the same drill sizes. So you are not changing as much as say changing a 94 to a 95.

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    gn7
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    Holley jets are rated by FLOW not drill size. Each jet size is suppose to represent a 2% change in flow. Jets that have the same drill size may have a different entry or exit chamfer. And a change from a #90 to 91 jet will flow a larger difference than a #80 to 81, because the 2% of the amount thru the 90 jet, is larger than 2% of the flow thru a 80. Holley jets are +/- 2% flow accuracy as well. Therefore, it requires a 2 jets size change to guarantee achange. So it is possible, due to tolerances, for a 90 to flow exactly the same or very close to a 91 or an 89.

    Holley did, and may still, sell close tolerance jets. each was flow checked and marked. They come in set of 3 for each size. One at the bottom of the flow tolerance, one in the middle and one at the top. With 2% spred across all three. 1% big and small from the middle jet. And they are $$$$$



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    Last edited by gn7; 07-30-2010 at 06:46 PM.

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    Liquid Louie flatcrzy's Avatar
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    Quote Originally Posted by obnoxious001 View Post
    I agree with Fiat,, I would not drop 4 sizes, safer to take smaller steps than to hurt the thing, particularly since you came on looking for advice.

    I think Burley is a corrected altitude of just over 4000 feet,, and one of my comp jet guys drops 2 sizes for the Burley race.

    Well I went out and ran it today but put the original jets back in it! I screwed up, I didn't pull the jets so it has 86s all the way around, now after a 12 pack of beer and reading shit with a flash light you can see how 86 can become 98 upside down! Anyway it's Beyond Scary ass fast when you open her up I never even got past 1/2 throttle because the Ol' lady was screaming to slow down.But it will not idel worth a shit you have to keep giving it gas or or it will die.

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