Formulas
The horsepower needed to overcome aerodynamic drag at a given speed is: HP = k*A*Cd*v^3
Where HP is horsepower, k is the density of air, A the frontal (crosssectional) area, Cd the coefficient of drag, and v the velocity. The density of air depends on conditions but is nominally .08 lb/ft^3.
Aerodynamic drag is calculated as: F = 1/2 CDAV^2
Where: F  Aerodynamic drag force, C  Coefficient of drag, D  Density of air (nominally about 0.08 pounds per cubic foot.. yes I know that's not a technically accurate mass but it saves converting to and then back from metric), A  Frontal area, V  Velocity of object
To estimate engine HP from 1/4 mile run: HP = ((trapspeed/234)^3) * weight
Tire Diameter in inches = ( ( Tire Width * Aspect Ratio ) / 25.4 ) * 2 + Wheel Diameter
Example: 245/4017 would be ( ( 245 * .40 ) / 25.4 ) * 2 ) + 17 = 24.71653543307
MPH = ( RPM * Tire Diameter ) / ( ( gear ratio * final drive ) * 336 )
Example: ( 8000 * 24.71653543307 ) / ( ( .771 * 4.062 ) * 336 ) = 187.9074535627 MPH
Of course the tires expand at high speeds so this isn't totally accurate.
VERY Rough Rules Of Thumb
Each 10 degree F drop in temperature = 1 % gain in HP
Each 10 lbs. removed from the vehicle = 1 HP for acceleration (top speed is not noticably affected)
Each 10 HP added = 0.1 second in the 1/4 mile
Conversions
Volume 


1 Imperial Gallon =  4.5461 liters (l) 
1 liter (l) =  0.2200 Imperial Gallons 
1 US Gallon =  3.7854 liters (l) 
1 liter (l) =  0.2642 US gallons 
1 Imperial Gallon =  1.2009 US Gallons 
1 US Gallon =  0.8327 Imperial Gallons 
1 liter =  61 Cubic Inches (ci) [approximate] 
Distance 

1 mile (mi) =  1.6093 kilometers (km) 
1 kilometer (km) =  0.6214 miles (mi) 
Fuel Consumption 

1 Mile/Imp. Gallon =  0.354 kilometers/liter (km/l) 
1 kilometer/liter (km/l) =  2.825 miles/Imp. Gallon 
1 mile/US gallon (mpg) =  0.425 kilometers/liter (km/l) 
1 kilometer/liter (km/l) =  2.352 miles/US gallon (mpg) 
Mass 

1 kilogram (kg) =  2.2046 pounds (lbs) 
1 pound (lb) =  0.4536 kilograms (kg) 
1 gram (g) =  0.0353 ounces (oz) 
1 ounce (oz) =  28.35 grams (g) 
Pressure 

1 pound/square inch (PSI) =  0.0689476 bars 
1 bar =  14.5037681 pounds/square inch (PSI) 
Power 

1 PS =  0.98632 HP 
1 HP =  1.01387 PS 
1 kgm =  7.23 lb. ft. 
1 lb. ft. =  0.14 kgm 