Engine How To Determine Cfm Requierment Carburator

Discussion in 'Classic Mustang Specific Tech' started by mhjo, Dec 12, 2013.

  1. I have a upgraded stock 289, Roller cam, roller lifters, dual plane intake, k/N filter, dual exhaust, Edelbrock heads, HiPo manifolds.

    I now have a Edelbrock 500 cfm carburator, but my mechanic says I'm loosing some HP because I need larger carburator. He suggest Holley 570.

    Any suggestions??
     
  2. How much cam did you use? What rear end gear are you using? What diameter of exhaust pipe? Why only hipo manifolds, and not headers? where are you driving the car? Around town, or on a road course or 1/4 mile strip?
     
  3. #4 mhjo, Dec 16, 2013
    Last edited: Dec 16, 2013
  4. 650 and be done
     
  5. 650??? Isn't that too much? The selector that Iskwezm posted suggests 570
     
  6. It doesn't need to be that precise. Besides, the stock 289HP carb was a little short of 600, and you've got a lot more cam than that. 600, or 650, would be just fine.
     
  7. How do one calculate the correct CFM (not using online calculators). Can someone enlighten me on the CFM thing?
     
  8. The problem with the online calculators is that none of them account for camshaft lift or duration, or cross section of intake manifold, different from stock valves, or lots of other factors that affect engine performance. Don't forget jet sizing too. A smaller carb will typically get better low end performance, and a larger CFM carb, will usually be better on the top end. The 65 Shelby with a 289, got a 715 CFM carb, and my 69 Cougar with 351W got a 470 CFM (4V) from the factory.
    So, I can't give you a specific mathematical equation to answer your question.
    There may be something here that will answer your question:

    http://www.carbdford.com/forum/index.php

    I would just go with the 650. I prefer the Holley's, but I have Edelbrock as well. If your car is an automatic, I would stick with a vacuum secondary.....
     
  9. Thanks. That's what I thought too about the calculators..