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Automotive Formulas

Discussion in 'Reference Materials' started by pissedoffsol, Mar 1, 2004.

  1. pissedoffsol

    pissedoffsol RETIRED

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    Found a cool site with a bunch of equations for solving for "stuff" :)

    orig posted on http://www.westernracing.com/reference/formulas.htm


    Automotive Formulas

    Formulas for displacement, bore and stroke:

    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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