Speed Demon 650 or 750 for this setup?

Discussion in 'Classic Mustang Specific Tech' started by allcarfan, Dec 10, 2003.


  1. allcarfan

    allcarfan The Answer Man Founding Member

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    lightweight 331 stroker
    Mildly ported twisted wedge heads (290/210cfm)
    xe274hr cam:
    * Advertised duration: 274 intake/282 exhaust
    * Duration at .050 in.: 224 intake/232 exhaust
    * Gross valve lift: .555 in. intake/.565 in. exhaust
    * Lobe separation: 112 degrees
    Ported and notched Performer RPM intake
    1 3/4" headers

    Engine will probably see 6700 rpms or so once in a while.

    So...Speed demon 650 or 750?

    I read an article where an engine made 400 at the flywheel and the 750 speed demon was too big.

    Shane
     
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  2. gp001

    gp001 Founding Member

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    650. My 347 makes about 400 fwhp and the 750 was too big for it as well.

    Using 331 ci, 6700 max rpm, and 100% ve the formula says 709 cfm. Using 90% ve it comes out to 567 cfm. I don't think you'll ever see 100% ve, and you would still be over carbed.
     
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  3. allcarfan

    allcarfan The Answer Man Founding Member

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    im probably going to be making closer to 475/500 hp at the flywheel. To my understanding the 650 flowed wet at 753cfm.

    Thanks for your explanation GP. It doesnt get much better than that.
     
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  4. foghorn67

    foghorn67 I'll save you the time and choke myself Founding Member

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    650. especially with them demons, they flow alot more then holleys.
     
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  5. brianj5600

    brianj5600 Active Member

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    A similar motor in MM/FF went over 100% ve. I would call tech at BG, they know there products better than any of us.
     
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  6. Clark

    Clark Founding Member

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    Defintely 650, I have a 625 Road Demon on my 393W and it runs good.
     
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