These are basic formulae from many sources collected over the years. Many have been improved with additional variables and used in the PS:Calc and PS:Calc Pro software. See the KEY at bottom.

ENGINE SIZE
CI = (bore/2)^2 * PI * stroke * cylinders

AIRFLOW
VE = CFM / (CI * RPM / 3456)
VE = Actual CFM / Calculated CFM * 100

CFM = CI / 3464 * VE * RPM * (1.2 single_plane intake OR 1.33 dual_plane)
Or if supercharged...
boost = (25.58 * BlowerCI * DriveRatio / CI) - 14.7
CFM = (CI * RPM / 3456) * (boost / 14.7 + 1)

HORSEPOWER
BHP = atmos_pres * CR * VE * CI / 5252 * RPM / 150.8
example
BHP = 14.7 * 8.5 * .8 * 355 / 5252 * 5000 / 150.8 = 224

BHP = CI * MEP * RPM / 792000
MEP = (BHP * 792000) / (RPM * CI)
or
BHP = (PLAN) / 33000
where P=MEP, L=stroke('), A=Piston area("^2), N=RPM*cyl/2 (4 cycle)

BHP loss for increase in altitude
BHP_Loss = altitude (thousands of feet) * .03 * BHP * -1

HP required for MPH in Quarter mile
HP_Req = ((.00426 * mph)^3) * weight

HP required for MPH (Aerodynamic loss)
HP_req = .0015 * CD * FA * (MPH^2)

GEARING
Tire size to Diameter conversion
tire_Diameter = Width (mm) * sidewall Height (%) / 25.4 * 2 + wheel_Diameter
Example: P205/60R15
205 * .60 / 25.4 * 2 + 15 = 24.685

MPH = tire_Diameter / 336 * rpm / gear_ratio
RPM = 336 * gear_ratio * mph / tire_Diameter
gear_ratio = tire_Diameter * rpm / 336 / mph

1/4 Mile ET / 1.54 = 1/8 Mile ET
Example: 14 / 1.54 = 9.09

KEY:

atmos_pres = Atmospheric Pressure in Pounds per Square Inch
BHP = Brake Horse Power (at flywheel)
 CD = Coefficient of Drag
CFM = Cubic Feet per Minute
 CI = Cubic Inch
 ET = Elapsed Time (Acceleration)
 FA = Frontal Area of vehicle in square feet
 HP = Horse Power (Net - at wheel)
MEP = Mean Effective Pressure
 PI = ~3.14159265
RPM = Revolutions Per Minute
 VE = Volumetric Efficiency