Speed Demon 650 or 750 for this setup?

Discussion in 'Fox 5.0 Mustang Tech' started by allcarfan, Dec 10, 2003.

  1. 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.

  2. You should see a little more than 400 FWHP, but I would go with the 650 and tinker with it(different jettings/spacers). I read in an article of a company that makes spacers that increase the cfm by ~30 and add a good amount of power across the range, I think it was in the new 5.0 issue.
  3. There was an article in a recent Car Craft where they made a 302 dyno 401fwhp. But the car revved to the moon and they did use a 750cfm carb. Im not sure why, but they did. I would stick with a 650 carb if it was my car. Good luck.
  4. 650 carb all the way. and yes those carb spacers are tapper inside to provide a smooth airflow from the carb to the intake, sort of like port matching, and the tappered carb spacers add a good amount of hp.

  5. FYI...the speed demon 650cfm carb wet flows more than a holley 4160 (750cfm) carb