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Thread: Equation for stubby bell mouth/velocity stack?

  1. #1
    Nova Scotia,Canada,Earth Blue's Avatar
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    Default Equation for stubby bell mouth/velocity stack?

    Anyone know the equation for the +5.8% 3/4" high profile of the stubby in this figure?

    (I found equations for traditional elliptical bell mouths but not for a stubby plate design like in the figure)




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    Interesting chart. At first glance that chart would seem to prove the old adage, "less is more". Do you have the link to the article with any descriptions of statistical models? It must be a science of infinite variables. The correlation coefficient such as a slight lip radius deviation alone would change the results drasticly. I've thought about this some, ever since I bought a Z from the Boston area from a guy who said his grandfather had done years of research and testing and had come up with the theory that the short stubby, home spun versions he had made, although crude, were very efficient. They were mounted on a triple set of Weber DCOE45s and fit nicely under the K&N filter housings. I still have that set. He had made me promise not to change a thing until I at least tried his set-up. I haven't yet but hope to one day and thought I might even try to improve on the design and make new ones.

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    Here is the latest for a traditional taller bellmouth/airhorn/velocity stack. (attached pdf)

    Here is one closely approximating Velocity stacks #2

    but still no detailed equation for the one in the drawing above from (David Vizard - How to tune the A-series engine , page 57 to 72 / The chapter called RAM CHARGING.)
    Attached Thumbnails Attached Thumbnails (Blair_and_Cahoon)_Design_of_an_intake_bellmouth_Sept._2006.pdf  
    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
    The person who buys on price alone is this man's lawful prey.


    John Ruskin (1819 - 1900)



    ZCars in Eastern Canada seaport ready for shipment to Europe

    http://ZSportCanada.com


  4. #4
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    Thanks for the link and attachment Blue. It is an interesting topic that at this point, I can only partially comprehend but enjoy reading and hearing the results of the testing just the same.

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    The design of the bell mouth is 1/4 of an ellipse from the edge of the carb/Throttle body to the outer most part of the air horn. It then curls into a circle. There are ratios of height to width of the bell mouth that determine the ellipse's curve aand best performance....and a rule of thumb for the curl.

    What is confusing me is the long (major) axis of the ellipse is parallel with the air flow on the newer bell mouth in the pdf where as the Vizard ellipse looks to be perpelndicular?
    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
    The person who buys on price alone is this man's lawful prey.


    John Ruskin (1819 - 1900)



    ZCars in Eastern Canada seaport ready for shipment to Europe

    http://ZSportCanada.com


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