Various Automotive Formulas

There are probably many different ways to calculate for any of the desired results. These are one I use.

Cubic Inch Displacement:  Bore x Bore x Stroke x 0.7854 x number of cylinders
Example:  4 x 4 x 3.480 x 0.7854 x 8 = 349.849 cubic inches

Cubic Inches to Liters:  Cubic Inches x 0.01639
Example: 350 x 0.01639 = 5.734 liters

Brake Horsepower:  Torque x RPM / 5252
Example:  400 x 5000 = 380.8 horsepower

Carburetor CFM Requirement:  (RPM x Cubic Inch Displacement x .8x) / 3654
(Note .80 to .85 is considered good volumetric efficiency of engine.)
Example:  (5000 x 350 x .85) / 3654 = 430.4 CFM

Miles Per Hour:  Two methods depending on what variables are known.
#1 (Tire Diameter x RPM) / (Final Gear Ratio x 336)
#2 (Tire Diameter x RPM x 0.002975) / Final Gear Ratio
Examples
#1 (27.0 x 3000) / (3.31 x 336) = 72.831 MPH

Final Gear Ratio:  Two methods depending on what variables are known.
#1 ((Tire Diameter x RPM) / MPH) / 336
#2 (Tire Diameter x RPM x 0.002975) / MPH
Example:
#1 ((27.0 x 3000) / 73) / 336 = 3.31

RPM:  Two methods depending on what variables are known.
#1 (Final Gear Ratio x 336) / (Tire Diameter / MPH)
#2 (MPH x Final Gear Ratio) / (Tire Diameter x 0.002975)
Example:
(3.31 x 336) / (27.0 / 73) = 3000 RPM

Horsepower required:  ((0.0426 x MPH) ^3) x Weight
Example: ((0.0426 x 70) ^3) x 3750lbs = 99.4 horsepower required