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Many of the formulas use the value of pi which is 3.1415927 | |
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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 (thanks to Bobby Mosher for this formula) 
   1/8 mile ET = 1/4 mile ET / 1.5832 (thanks to Bobby Mosher for this formula) 
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 = actual cfm / theoretical cfm x 100 
street carb cfm = rpm x displacement / 3456 x 0.85 
racing 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 
driveshaft torque = flywheel torque x transmission ratio 
Formula for instrument error 
actual mph = 3600 / seconds per mile 
speedometer error percent = difference between actual and indicated speed / actual speed x 100 
indicated distance = odometer reading at finish - odometer reading at start 
odometer 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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