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Updated the FMU page on redz31.com

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  • Updated the FMU page on redz31.com

    Updated the FMU page here with a question I was recently asked:

    http://www.redz31.com/pages/fuel/fmu.html

    Questions, comments, etc?

  • #2
    font sizes are screwy....

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    • #3
      My shop is right next to Cartech.
      BLOZ UP.com
      It is not recommended to confirm proper installation by driving into walls or other barriers as this could cause personal injury or damage to the vehicle.

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      • #4
        >fuel consumption does increase slightly with more timing
        It's RWD in reverse.

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        • #5
          j30_vg33et wrote: >fuel consumption does increase slightly with more timing

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          • #6
            Hmmm. Well, yeah, I see what you're saying.

            I guess it just seems that as timing approaches an optimum value, BSFC goes down. Thus you're just making better use of the fuel in the chamber.

            But you're saying that due to the increased fuel fraction burned, additional fuel should be put in for cooling.

            Sound right?

            BTW, shouldn't you be sleeping? My sorry ass is still at work...
            It's RWD in reverse.

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            • #7
              If you experiment on your own, you'll see that the increased timing will actually tend to (very slightly) lean out the mixture. This is my general experience.

              I'm also of the belief the 'extra' fuel is not really cooling the charge as some people think. The cooling due to vaporization of that tiny amount of fuel is having such a tiny effect on the temperature of the charge. Calculate the latent heat and figure based on the AFR; it's less than one degree. The additional fuel just makes a denser mixture and hence the flame front moves through it slower which in effect does the same thing as retarding the ignition timing.

              Innovate tech tends to agree as well, I think he put it very well in this article:
              http://www.innovatemotorsports.com/resources/rich.php

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              • #8
                Jason84NA2T wrote: If you experiment on your own, you'll see that the increased timing will actually tend to (very slightly) lean out the mixture. This is my general experience.
                to an o2 sensor yes it will seem leaner, since it detects the combustables after combustion, the sooner the burn starts the sooner all the fuel is combusted, retarding timing will always mean some fuel gets wasted, dumped into the exhaust, and this will be whether your engine is struggling or knocking, the o2 only cares about the gas in the pipe

                Jason84NA2T wrote:
                I'm also of the belief the 'extra' fuel is not really cooling the charge as some people think. The cooling due to vaporization of that tiny amount of fuel is having such a tiny effect on the temperature of the charge.
                not in our case since 1. we are batch injection, 2. the injectors are right next to the valves....

                the only time fuel will cool the charge is in a tbi application where it is dumped in to an intake long before any obstruction, and the air will thoroughly mix with it as it tries to evaporate, this also happens on carbed vehicles but more or less effectively since the fuel isn't atomized by a high pressure squirt

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                • #9
                  I'm thinking that G-E and I are saying the same thing about A/F.

                  Further, it would reason that if your injector is putting the same amount of fuel into the same amount of air, and all you're changing is timing, any difference seen in A/F on the wbo2 is due to it's interaction with the exhaust species. By definition, the A/F remains the same.

                  Good points about fuel cooling. BTW, thanks for the linky to the inovative article.
                  It's RWD in reverse.

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                  • #10
                    in our engine most the fuel puddles on the intake valves, with just a little bit being injected with it open, we really don't get any significant atomization and therefore cooling effect prior to entering the chamber

                    this of course doesn't preclude installing a 7th injector next to the t/b with a controller ....

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