AFR's
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AFR's

  1. #1
    Member Wetnreckless's Avatar
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    Default AFR's

    Having trouble finding a general consensus on " safe " air fuel ratios for
    blower motors. Not looking to squeeze a tenth, or every ounce of horsepower out of it, but without the benefit of a dyno just looking for a
    starting point from people more knowledgeable than I am.

    Particulars : 468 Chevy 7.5 to 1, solid roller 640 lift, 256 dur.,alum.heads
    871 ( no intercooler ) 2 825 cfm demons, msd 6al and dist. @ 32* total
    by 2,600 rpm. Trying to stay on pump gas.
    Making 8 lbs. boost @ 6,100 rpm in a flat keel Daytona
    with a mag bronze " B "

    Have been pointed in the direction of afr's of :
    Idle - 3,000 rpm no load 13.5
    Cruise - 12.3 - 12.5
    WOT - 11.3 - 11.5
    Sound reasonable ? Thanks for any help.

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    Member Wetnreckless's Avatar
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    Thanks gn7, I guess with those numbers i'm probably leaving some power on the table but at this point I would rather be safe than sorry and not have to build another motor. Danny

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    mo balls than $cents$ IMPATIENT 1's Avatar
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    x2 afr's are lookin nice to me

    Dare to be different, if it turns out great you can claim you planned it that way.

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    Senior Member ap67et10's Avatar
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    Quote Originally Posted by IMPATIENT 1 View Post
    x2 afr's are lookin nice to me

    if this had efi, i'd tell you that your wasting a ton of money on gas! but since its a carb you need to tune for WOT primarily and where the rest falls, it falls.

    Andrew

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    Senior Member STV_Keith's Avatar
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    If cruise is not on boost, I'd be shooting for 12.5-12.8 and WOT, 11.5-11.7.
    Keith-


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    Senior Member Hass828's Avatar
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    Quote Originally Posted by STV_Keith View Post
    If cruise is not on boost, I'd be shooting for 12.5-12.8 and WOT, 11.5-11.7.
    Thats almost were he's at, just a slight tad fat which is probably fine.
    But Andrew could make him cruise at 14.5-1
    "if we keep doing it the same way we always do..we will always get the same results"
    H8-2-W8
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    Senior Member ap67et10's Avatar
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    Quote Originally Posted by Hass828 View Post
    Thats almost were he's at, just a slight tad fat which is probably fine.
    But Andrew could make him cruise at 14.5-1
    I could...or 17:1 or even 9:1...all at the click of a button. But this conversation doesn't apply here.....its got carbs!
    Last edited by ap67et10; 07-22-2010 at 04:09 PM.

  11. #9
    Senior Member Hass828's Avatar
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    Quote Originally Posted by ap67et10 View Post
    I could...or 17:1 or even 9:1...all at the click of a button. But this conversation doesn't apply here.....its got carbs!
    dont be jealous

    If you save up you can get you one too.
    "if we keep doing it the same way we always do..we will always get the same results"
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  12. #10
    gn7
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    Quote Originally Posted by STV_Keith View Post
    If cruise is not on boost, I'd be shooting for 12.5-12.8 and WOT, 11.5-11.7.
    Quote Originally Posted by Hass828 View Post
    Thats almost were he's at, just a slight tad fat which is probably fine.
    But Andrew could make him cruise at 14.5-1
    I am with you Hass. Is this a hair splitting contest. Because if it is, I say he should richen up the WOT to 11.27995 to 1



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  13. #11
    Senior Member Hass828's Avatar
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    Quote Originally Posted by gn7 View Post
    I am with you Hass. Is this a hair splitting contest. Because if it is, I say he should richen up the WOT to 11.27995 to 1
    Yea, you know GN7, one of the big things I hear about the EFI is how long they make an engine last, which I believe to be true in a stock unmodified situation where a carb might be way to fat from the get go and kills the engine before it ever made 100,000 miles(in the old days) .
    BUT, if you spend just a little bit of time and tune a carb once , the engine will last too.
    I have a 454 that I got when I bought an old wore out 74' model truck from a farmer, had 140,000 hard miles on it and the engine was the only thing that worked. doors wouldnt close,no lights,windows wouldnt roll down, tailgate bashed, it was as wore out as it could get but that engine & turbo 400 still ran suprisingly well. I pulled it out, ran a ball hone through the cylinders , put new rings & bearings, presses new iron guides in the heads and had a valve job done, put a small isky cam, headers, aluminum performer rpm intake and a new 750 vac sec holley, and a cheater nos plate. This was like 18-20 yrs ago, the SOB has now wore this truck out. And I used to tow my big enclosed trailer to the drag races with it and unhook while there and race the other street guys with it (on the NOS) then hook back up and tow back home.
    It put another 135,000 hard miles on this truck, and I've ran tons of NOS through it. The old SOB is still all standard bore & crank. Still runs good today.
    I dont know if it would have lasted longer if it were efi but if it did I probably wouldnt be around to see it,lol.
    "if we keep doing it the same way we always do..we will always get the same results"
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  14. #12
    mo balls than $cents$ IMPATIENT 1's Avatar
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    not all carbs are equal, and this we know put it on blow thru and he can go from 15lbs up to 32lbs and all he'd have to touch is the pressure regulator to fatten up or lean out +/- .5 afr and that change will be throwout the carb's range , under a load and without 1, been there doin that efi would take 2 rocket scientists, a electrical engineer, and 3 polocks to get er done breaking out the leatherman multitool bunchsssss easier than breaking out the laptop on the lake

    Dare to be different, if it turns out great you can claim you planned it that way.

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    Highaboosta Unchained's Avatar
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    OK here's a poll,

    How many actually OWN and USE a wide band O2 sensor to tune with ?

    Twin Turbo 1800 HP V-Drive lake boat

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    Quote Originally Posted by Trigger View Post
    No one cares about your buddies old antiquated garden hose technology.
    Quote Originally Posted by MAXIMUS View Post
    I think I could run more boost but it's a real hand full right now

  16. #14
    Senior Member ap67et10's Avatar
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    Quote Originally Posted by IMPATIENT 1 View Post
    not all carbs are equal, and this we know put it on blow thru and he can go from 15lbs up to 32lbs and all he'd have to touch is the pressure regulator to fatten up or lean out +/- .5 afr and that change will be throwout the carb's range , under a load and without 1, been there doin thatefi would take 2 rocket scientists, a electrical engineer, and 3 polocks to get er done breaking out the leatherman multitool bunchsssss easier than breaking out the laptop on the lake


    I will take that as a complement!! thanks Tom, did know you thought so highly of us EFI guys!

    AP

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