Automotive Formulae by Dino
1) Estimating wheel horsepower from top speed
HORSEPOWER (Wheels) = (6.114.W.V + Cd.A.V3)/149877
(x1.11 manual gearbox FWD, x1.17 manual gearbox RWD, x1.17 automatic gearbox FWD, x1.25 automatic gearbox RWD for flywheel horsepower)
W= Test weight (lb), V= Top speed (mph), Cd=Drag coefficient, A= Frontal area (ft2).
2) Estimating flywheel horsepower from 0-60 time
HORSEPOWER (Flywheel) = (0.413.W)/T0-60
T0-60 = 0-60 mph time (sec).
3) Estimating wheel horsepower from 1/4 mile trap speed
HORSEPOWER (Wheels) = W. [Mph/247]3
4) Estimating wheel horsepower from 1/8 mile trap speed
HORSEPOWER (Wheels) = W. [Mph/196]3
5) Relationship between barometric pressure and elevation
BP = BP0.e -0.0104.H/K
BP= Barometric pressure, BP0= Pressure (sea level), H= Elevation (ft), K= Air temperature (K) = 273+oC.
6) Dyno horsepower correction factor for air temperature, pressure and humidity
Air correction factor = [29.92”Hg/(BP-WVP)]. [(459.7+ AIT)/519.7]0.5
AIT= Air intake temperature (oF), WVP= water vapour pressure.
7) Relationship between flywheel horsepower and compression ratio
Horsepower change (%) = [1- 1/Rnew0.4]/[1-1/Rorig0.4] -1 x100%
R= Compression Ratio.
8) Calculation for rear wheel torque
Torque (Wheels) = (W.G.A)/1545
W= Vehicle & driver weight (lb), G= Gearing (mph/1000rpm), A= Acceleration (mph/sec)
9) Formula for mph, rpm, overall gear ratio and tire diameter
Mph = [rpm x tire diameter(in.)]/[overall gear ratio x 336]
10) Calculation for optimum overall gearing
Overall gear ratio = (tire diameter x maximum rpm)/(mph1/4 x 340)
mph1/4= 1/4 mile trap speed calculated using formula 3) where weight and horsepower are known