Auto Math Formulas

  • Displacement
     = bore2 x stroke x .7854 x # of cylinders

  • RPM
     = mph x axle ratio x 336 x transmission gear ratio / loaded tire diameter

  • MPH
     = (rpm x 60) / (axle ratio x tire revolutions per mile)

  • Tire Revs Per Mile
     = 10084 / loaded tire radius

  • Carburetor CFM Requirements
     = displacement x redline rpm x volumetric efficiency (90%, or .9 for a good street car) / 3456

  • Coil Spring Rate
     = (W x G) / (8 x N x D) where:
    W = wire diameter (in.)
    G = 12,000,000
    N = number of free coils* + 0.5
    D = diameter of spring coil (from center to center of wire)
    * "free coils" is the number of coils in the spring which don't touch the mount. Generally, the top and bottom coils aren't counted as "free coils".

  • Skidpad performance:
     g = (1.225 x R) / (T x 2) where:
    g = lateral acceleration force (in percentage of one gravity)
    R = radius of circle competed
    T = time in seconds to complete circle

    If there any more formulas you'd like to see on this list, or any that you may already have and would like us to post, feel free to contact us.

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    Copyright © 2009 Bruce Johnson and Craig Watson