Your Free C.F.M. Calculator


  • 1
    Myth: -installing a larger carburetor increases horsepower.

    Truth: The amount of air flowing into your engine is not dependent on the size of your carburetor but is determined by the size of your engine, the C.I.D. (cubic inch displacement) and R.P.M (revolutions per minute) that it is spinning at.

  • 2
    First figure out the exact size of your engine C.I.D. - Cubic Inch Displacement
    • C.I.D. = Bore squared x stroke x .7854 x number of cylinders
    • e.g.-----------bore x bore x stroke x .7854 x 8 cyl.
    • S.B.C.= 4 x 4 x 3.484 x .7854 x 8 = 350.25 cid
  • 3
    C.F.M. calculator The following formula will define the C.F.M. (cubic feet per minute) of air/fuel mixture your engine draws based upon your engines specific parameters. You can now determine what size of carburetor you should use for your application.

C.F.M. calculator

  • C.F.M. = Engine Size (C.I.D.)
  • times maximum R.P.M.
  • divided by 3456

e.g. (S.B.C.)-------350cid x 6000rpm รท 3456 = 608 c.f.m.


Using a carburetor that is too large can be harmful to your engine as most larger carburetors are often jetted richer which will cause your spark plugs to foul and will promote fuel wash resulting in piston ring and cylinder wall damage.

As seen in the example above a small block Chev. running at 6000 RPM max. will work best using a 600 C.F.M. carburetor.

Use this chart

Find your engine size on the left, then pick you maximum RPM on the top and draw lines to meet at your recommended C.F.M.

This chart will not show properly on small screens

c.f.m. calculator