GPM change with lower compression

Discussion in 'PSI Superchargers Tech Questions' started by ZERO260IN1, Feb 19, 2009.

  1. ZERO260IN1

    ZERO260IN1 Member

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    GPM change with lower compression


    548 BBC, 13:1cr, 28 degrees , Littlefield 1471 K11, going down to 11.75cr, how much fuel would you pull away to keep the tune up similar? 9.4gpm to the motor right now.

    Im thinking of .3 less just for starters. Any input?
     
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    Last edited: Feb 19, 2009
  2. Creech

    Creech Member

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    9.4 gallons? How long of track, is this a sand dragster?
     
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  3. ZERO260IN1

    ZERO260IN1 Member

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    Door car, 1/4mile, and yes 9.4 gpm tune up :cool:
     
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  4. aj481x

    aj481x Member

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    I would consider adding a degree of timing, not changing the fuel, and make a lap. Your plugs should show you where to go.
     
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  5. SoDak

    SoDak Active Member

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    I think your pretty close by taking out .3 gpm. By my figures you'll still be a little rich. If it were mine I would probably take out .3 expecting to take out a little more.

    Why are you taking compression out?
     
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  6. ZERO260IN1

    ZERO260IN1 Member

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    Thanks for the comments



    Why? I’m a victim of the “ your running HOW much compression” LOL

    Truth be told, it ran fine… but thinking I must be fat with no color on the plugs and Im looking for more performance, I take .2 of a gallon out of it, and it goes from no cad burn to ¾ of a ring. I dunno, Not enough laps for me to come to a good conclusion on where my tune up is really sitting.

    So far the relatively new combo is an underachiever IMO and I want to “lean” on it for a lack of a better term, and feel the lower compression will be more lenient. Hopefully I don’t make this thing a turd by taking out static :)

    Input
     
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  7. Mike Canter

    Mike Canter Top Dragster
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    ZERO260IN1, you have never said how much boost you are running.
    So what is your OD?
    How much boost at 8000 RPM in 3rd gear?
    Do you have a flow sensor? Is that GPM at 8000 RPM off the flow meter or is it a guess?
     
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  8. ZERO260IN1

    ZERO260IN1 Member

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    Flowed fuel system from Davenport. Using Jetsize, Im putting 9.4gpm in the motor at 3000feet DA

    Its 24%over, and patheticly I dont have the boost numbers at 8000rpm, no data logger yet. Hopefully the combo gives you a few hints on where it typically should be. (cough cough , going to guess 25psi) :D
     
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  9. Mike Canter

    Mike Canter Top Dragster
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    Yes, I would say your CR is a little high. It would be a lot safer to be down somewhere 11.5 to 11.7. It would give you a safer tuning window.
     
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