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Thread: Carburetor Bell Mouth Design

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    Carburetor Bell Mouth Design

    Hi all,

    A few people noticed the Bell Mouth I had made for my carburetor (mostly coz I was constantly showing it off) at the last race meet at Mt Welly. I thought I'd be a good sport and share the details of its design for others to have a go at making their own.

    I found an article (see link) that showed some pretty snazzy computer modelling of the effect of various shapes on flow performance. The really good thing is that on the second page they give three options to use depending on how keen you are to get a nice opening for your carb; a really basic tube with rounded end, an eliptical design (which is what I used) and a high-tech equation driven profile.

    All you need to know really is the internal diameter of your carby and away you go pretty much, the tricky part is getting it to fit onto your carb, and making it. Luckily I know a guy with a 3D printer so that solved that issue

    Here's the article:
    http://www.profblairandassociates.co...mouth_Sept.pdf

    And here's a picture of mine fitted to my carb.
    20160807_172159 - Copy.jpg

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    Brendan (24-08-2016)

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    Senior Member Yow Ling's Avatar
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    Good work, and very scientific. I got my bellmouth shape from a trumpet, then made it from fiberglass

    2015-03-06 17.37.01.jpg2015-02-22 11.09.01.jpg
    chaos will take a long time to restore
    george w bush

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    Administrator Brendan's Avatar
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    That's real cool and nice looking!!

    I have a 3d printed one also, i'll grab a pic at some stage and post up.

    Quote Originally Posted by CunninghamJames007 View Post
    Hi all,

    A few people noticed the Bell Mouth I had made for my carburetor (mostly coz I was constantly showing it off) at the last race meet at Mt Welly. I thought I'd be a good sport and share the details of its design for others to have a go at making their own.

    I found an article (see link) that showed some pretty snazzy computer modelling of the effect of various shapes on flow performance. The really good thing is that on the second page they give three options to use depending on how keen you are to get a nice opening for your carb; a really basic tube with rounded end, an eliptical design (which is what I used) and a high-tech equation driven profile.

    All you need to know really is the internal diameter of your carby and away you go pretty much, the tricky part is getting it to fit onto your carb, and making it. Luckily I know a guy with a 3D printer so that solved that issue

    Here's the article:
    http://www.profblairandassociates.co...mouth_Sept.pdf

    And here's a picture of mine fitted to my carb.
    20160807_172159 - Copy.jpg

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    Administrator Brendan's Avatar
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    Quote Originally Posted by Yow Ling View Post
    Good work, and very scientific. I got my bellmouth shape from a trumpet, then made it from fiberglass

    2015-03-06 17.37.01.jpg2015-02-22 11.09.01.jpg
    yer, naaa, it don't look quite the same!!

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    Thanks Brendan, I do like the Trumpet idea tho. I was originally going to turn some sort of wooden form on the lathe to make a fiber glass one, and then my mate came in to save the day with the printer.

    Here's a snap shot of the CAD model I made for 3D printing it.
    Bell mouth.jpg
    Bell mouth 2.jpg

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    Brendan (26-08-2016)

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    i made mine from a glass , had nice whisky in it
    (-;

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    Care to share the print file?


    Calvert86

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    Bellmouth.zip
    Quote Originally Posted by Calvert86 View Post
    Care to share the print file?
    Sure thing (attached). For some reason my computer won't let me upload the STL, but I managed to attached an IGES which will get you mostly there. Note that it's bespoke to my carby, and it will need tweaking accordingly.

    It's a bugger i can't upload the SolidWorks file (too big even when zipped) because it has equations driving the ellipse curves to scale it. If anyone has any bright ideas about uploading large files then I can give that a go.

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    Bellmouths.jpgThere's more than one way to do it...
    Pressed these out today. 3mm wall 6061 alloy tube in a size where the ID doesn't need to be touched to match the carb.
    40mm long, recess machined at the carb end to suit the body OD. The main portion of the length is then machined to approx 1.8mm wall thickness - taking it off the OD. Lightly polished on the lathe to assist pressing.
    Pressed onto a male form made up in mild steel and highly finished. Well lubed when pressing.
    I've done bigger ones before and it's possible to get an impressive flare on the end before it splits...

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    masterblaster (21-09-2016)

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    Pressed onto a male form made up in mild steel and highly finished.
    That's awesome, looks mint too. Any pics of the forms you used? Or even of the process in action?

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