Some formulas contain notation
such as ^2 which means "squared" or ^3 which means
"cubed"
Formulas for
Calculating Performance
Convert between 1/4 mile
and 1/8 mile ET's
1/4 mile ET
= 1/8 mile ET x 1.5832
1/8 mile ET
= 1/4 mile ET / 1.5832
Calculate 1/4 mile ET and MPH from HP and Weight
ET =
((Weight / HP)^.333) * 5.825
MPH = ((HP
/ Weight)^.333) * 234
Calculate HP From ET and Weight
HP =
(Weight / ((ET/5.825)^3))
Calculate HP From MPH and Weight
HP = (((MPH
/ 234)^3) * Weight)
Formulas for
displacement, bore and stroke
pi/4 = 0.7853982
cylinder volume = pi/4 x
bore^2 x stroke
stroke = displacement / (pi/4
x bore^2 x number of cylinders)
Formulas for
compression ratio
(CylVolume + ChamberVolume) /
ChamberVolume
cylinder volume = pi/4 x
bore^2 x stroke
chamber volume = cylinder
volume / compression ratio - 1.0
displacement ratio = cylinder
volume / chamber volume
amount to mill = (new disp.
ratio - old disp. ratio / new disp. ratio x old disp. ratio)
x stroke
Formulas for
piston speed
piston speed in fpm = stroke
in inches x rpm / 6
rpm = piston speed in fpm x 6
/ stroke in inches
Formulas for
brake horsepower
horsepower = rpm x torque /
5252
torque = 5252 x horsepower /
rpm
brake specific fuel
consumption = fuel pounds per hour / brake horsepower
bhp loss = elevation in feet
/ 1000 x 0.03 x bhp at sea level
Formulas for
indicated horsepower & torque
horsepower = mep x
displcement x rpm / 792,00
torque = mep x displacement /
150.8
mep = hp x 792,000 /
displacement x rpm
mep = hp x 792,000 /
displacement x rpm
mechanical efficiency = brake
output / indocated output x 100
friction output = indicated
output - brake output
taxable horsepower = bore2 x
cylinders / 2.5
Formulas for air
capacity & volumetric efficiency
theoretical cfm = rpm x
displacement / 3456
volumetric efficiency =
acutal cfm / theoretical cfm x 100
street carb cfm = rpm x
displacement / 3456 x 0.85
racin carb cfm = rpm x
displacement / 3456 x 1.1
Formulas for tire
size & their effect
effective ratio = (old tire
diameter / new tire diameter) x original ratio
actual mph = (new tire
diameter / old tire diameter) x actual mph
Formulas for g
force & weight transfer
drive wheel torque = flywheel
torque x first gear x final drive x 0.85
wheel thrust = drive wheel
torque / rolling radius
g = wheel thrust / weight
weight transfer = weight x cg
height / wheelbase x g
lateral acceleration = 1.227
x raduis / time^2
lateral weight transfer =
weight x cg height / wheel track x g
centrufugal force = weight x
g
Formulas for
shift points
rpm after shift = ratio shift
into / ratio shift from x rpm before shift
drivehsaft torque = flywheel
torque x transmission ratio
Formula for
instrument error
actual mph = 3600 / seconds
per mile
speedo error percent =
difference between actual and indicated speed / actual speed
x 100
indicated distance = odometer
reading at finish - odometer reading at start
odo error percent =
difference between actual and indicated distances / actual
distance x 100
Formulas for MPH
RPM gears & tires
mph = (rpm x tire diameter) /
(gear ratio x 336)
rpm = (mph x gear ratio x
336) / tire daimeter
gear ratio = (rpm x tire
diameter) / (mph x 336)
tire diameter = (mph x gear
ratio x 336) / rpm
Formulas for
weight distribution
percent of weight on wheels =
weight on wheels / overweight x 100
increased weight on wheels =
[ distance of cg from wheels / wheelbase x weight ] + weight
Formulas for
center of gravity
cj location behind front
wheels = rear wheel weights / overall weight x wheelbase
cg location off-center to
heavy side = track / 2 - [ weight on light side / overall
weight ] x track
cg height = [ level wheelbase
x raised wheelbase x added weight on scale / distance raised
] x overall weight
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