Various Automotive Formulas
There are probably many different ways to calculate for any of the desired results. These are one I use. You might also check my Tools page HERE for interactive calculators.
Cubic Inch Displacement
How to calculate your engine's cubic inches displacement and how to convert that to liters.
Cubic Inch Displacement: Bore x Bore x Stroke x 0.7854 x number
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
Some of the more popular Chevrolet engine sizes.
What is my theoretical brake horsepower?
Brake Horsepower: Torque x RPM / 5252
Example: 400 x 5000 = 380.8 horsepower
Carburetor CFM Requirements
How big of a carburetor do you really need in normal circumstances? Everyone assumes 'bigger is better' but it's very easy to go too big with a carburetor. Naturally your altitude above sea level, driving conditions, engine mods, and much more come into play when choosing a carburetor; this formula is just a starting point.
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
Calculate Miles Per Hour
Miles Per Hour: Two methods depending on what variables are
#1 (Tire Diameter x RPM) / (Final Gear Ratio x 336)
#2 (Tire Diameter x RPM x 0.002975) / Final Gear Ratio
Example #1 - (27.0 x 3000) / (3.36 x 336) = 71.747 MPH
Calculate Final Gear Ratio
Final Gear Ratio: Two methods depending on what variables are
#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)
(3.31 x 336) / (27.0 / 73) = 3000 RPM
Horsepower required: ((0.0426 x MPH) ^3) x Weight of
Example: ((0.0426 x 70) ^3) x 3750lbs = 99.4 horsepower required