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  1. #1
    jdog800's Avatar
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    Usefull engine formulas and porting software

    Thought this might come in handy for those who like to do it themselves.
    Predicting Power

    BHP = PLAN/33,000
    P is brake mean effective pressure, in PSI
    L is piston stroke, in feet
    A is the area of one piston, in square inches
    N is the number of power strokes per minute



    Piston Speed

    Cm = .166 x L x N
    Cm is mean piston speed, in feet per minute
    L is stroke, in inches
    N is crankshaft speed, in RPM

    Brake Mean Effective Pressure (BMEP)

    2-Stroke BMEP = (HP x 6500)/(L x RPM)
    4-Stroke BMEP = (HP x 13000)/(L x RPM)



    L = Displacement in Liters

    i.e., 80 cc = .08 Liters
    1 ci. = 16.39 cc

    Piston Acceleration

    Gmax = ((N^2 x L)/2189) x (1 + 1/(2A))
    Gmax is maximum piston acceleration, in feet per second squared
    N is crankshaft speed, in RPM
    L is stroke, in inches
    A is the ratio of connecting rod length, between centers, to stroke



    Piston Stroke Motion
    S = R cos X + L cos Z
    S = the distance piston wrist pin is from center of crankshaft
    R = the radius of the crankshaft wrist pin
    L = the length of the connecting rod
    X = the angle of the wrist pin
    Z = the angle of the connecting rod
    or
    sin X = R/L sin Z

    Piston Travel vs. Crank Rotation

    d = ((S/2) + L) - (S/2 cos X) - L sin[cos-1 (S/2L sin X)]
    S = Stroke (mm)
    L = Connecting Rod Length (mm)
    X = Crank Angle Before or After TDC (deg)
    Note: (L) Rod Length is usually 2 times the (S) Stroke
    OR
    For Spreadsheets and some Calculators
    HT = (r + c) - (r cos (a)) - SQRT(c^2 - (r sin (a))^2)
    r = s/2
    dtor = PI/180
    a = d x dtor
    HT = The height of piston
    r = The stroke divided by 2
    c = The rod length
    a = The crank angle in radians
    d = The crank angle in degrees
    dtor = Degrees to Radians



    Exhaust Systems Tuned Length

    Lt = (Eo x Vs) / N
    Lt is the tuned length, in inches
    Eo is the exhaust-open period, in degrees
    Vs is wave speed in feet per second (1700 ft/sec at sea level)
    N is crankshaft speed, in RPM
    Length of Curved Pipe
    L = R x .01745 x Z
    L is length
    R is radius of the pipe bend
    Z is the angle of the bend
    Diffuser Proportions
    D2 = SQRT( D1^2 x 6.25 )
    D2 is the diffuser outlet diameter
    D1 is the diffuser inlet diameter
    6.25 is the outlet/inlet ratio constant
    Baffle Cones
    Lr = Le/2
    Lr is mean point of the reflection inside the baffle cone
    Le is the length of the baffle cone

    Port Open Time

    T = ( 60/N ) x ( Z/360 ) or T = Z/( N x 6)
    T is time, in seconds
    N is crankshaft speed, in RPM
    Z is port open duration, in degrees



    Compression Ratio

    CR = ( V1 + V2 ) / V2
    CR is compression ratio
    V1 is cylinder volume at exhaust closing
    V2 is combustion chamber volume

    Carburetor Throttle Bore Diameter

    D = K x SQRT( C x N )
    D is throttle bore diameter, in millimeters
    K is a constant ( approx. 0.65 to 0.9, derive from existing carburetor bore)
    C is cylinder displacement, in liters
    N is RPM at peak power



    Crankcase Volume

    Primary compression ratio =
    Case Volume @ TDC / Case Volume at BDC
    or
    CRp = V1 + V2 / V1
    CRp is the primary compression ratio
    V1 is crankcase volume @ BDC
    V2 is piston displacement

    Resonance Effects

    F = Vs / 2╣ * the square root of A / Vc (L + 1/2 the square root of ╣ A
    Vs is the sonic speed Uusually about 1100 ft/sec)
    A is the cross-sectional area of the inlet
    L is the inlet pipe length
    Vc is the flask (crankcase) volume



    Average Exhaust Temperature

    Determine the exhaust gas temperature in Kelvin
    (k = C + 273.15). This is usually a function of the engine's BMEP.

    Torque

    1.00 lb-ft = 0.138 kg-m = 1.35 N-m
    1.00 kg-m = 7.23 lb-ft. = 9.81 N-m
    1.00 N-m = 0.102 kg-m = 0.737 lb-ft



    Mass

    1.00 lb = 0.454 kg = 4.45 N
    1.00 kg = 2.20 lbs = 9.81 N
    1.00 N = 0.102 kg = 0.220 lb

    Distance

    1 in = 2.54 cm = 0.0000158 mi = 0.0000254 km
    1 cm = 0.394 in = 0.00000621 mi = 0.00001 km
    1 ft = 30.5 cm = 0.000189 mi = .000305 km
    1 mi = 63,360 in = 160,934.4 cm = 1.609 km
    1 km = 0.621 mi = 100,000 cm = 3281 ft



    Pressure

    1.00 bar = 14.5 psi = 1.02 kg/sq-cm = 100 kPa
    1.00 psi = 0.069 bar = 0.070 kg/sq-cm = 6.89 kPa
    1.00 kg/sq-cm = 0.980 bar = 14.2 psi = 98.1 kPa
    1.00 kPa = 0.010 bar = 0.145 psi = 0.010 kg/sq-cm

    Temperature

    F = 9 / 5 x C + 32
    C = 5/9 (F - 32)
    K = C + 273.4



    Area / Volume

    1.00 sq-in = 6.452 sq-cm
    1.00 sq-cm= 0.155 sq-in
    1.00 cu-in = 16.387 cc
    1.00 cc = 0.0610 cu-in

    Power

    1.00 HP = 746 W
    torque (lb-ft) = 5252 x hp / rpm
    hp = rpm x torque (lb-ft) / 5252


    The Weight of Air

    14.7 lbs. per sq. inch at sea level.

    Air Density Calculation

    StdAirDensity = 1.22556 and is defined at 59.0F degrees, 0.0% humidity, and 29.92 inches on the barometer.

    Temp_c = (Temp-32.0) * 5.0 / 9.0;
    Temp_k = Temp_c + 273.0;
    Baro_mb = Barometer / (29.92 / 1013.0);
    Baro_pa = Baro_mb * 100.0;
    SaturationPressure_mb = 6.11 * pow(10,(7.5*Temp_c)/(237.7+Temp_c));
    VaporPressure_mb = Humidity * SaturationPressure_mb / 100.0;
    TempVirtual_k = Temp_k / (1.0 - (VaporPressure_mb/Baro_mb)*(1.-0.622));
    // D = P/(T*R)
    AirDensity = Baro_pa / (TempVirtual_k*GasConstant);
    % Std Density = AirDensity/StdAirDensity*100

    Additional Conversion Factors

    1 Centimeter - 0.0328084 foot; 0.393701 inch

    1 Circular Mil - 7.853982 x 10 to the negative seventh square inches; 5.067075 x 10 to the negative sixth square centimeters

    1 Cubic Centimeter - 0.061024 cubic inch; 0.270512 dram (U.S. fluid); 16.230664 minims (U.S.); 0.999972 milliliter

    1 Cubic Foot - 0.803564 bushel (U.S.); 7.480520 gallons (U.S. liquid); 0.028317 cubic meter; 28.31605 liters

    1 Cubic Inch - 16.387064 cubic centimeters

    1 Cubic Meter - 35.314667 cubic feet; 264.17205 gallons (U.S. liquid)

    1 Foot - 0.3048 meter

    1 Gallon (U.S. liquid) - 0.1336816 cubic foot; 0.832675 gallon (British); 231 cubic inches; 0.0037854 cubic meter; 3.785306 liters

    1 Grain - 0.06479891 gram

    1 Gram - 0.00220462 pound (avoirdupois); 0.035274 ounce (avoirdupois); 15.432358 grains

    1 Hectare- 2.471054 acres; 1.07639 x 10 to the fifth square feet

    1 Inch - 2.54 centimeters

    1 Kilogram - 2.204623 pounds (avoirdupois)

    1 Kilometer - 0.621371 mile (statute)

    1 Liter - 0.264179 gallon (U.S. liquid);0.0353157 cubic foot; 1.056718 quarts (U.S. liquid)




    1 Meter - 1.093613 yards; 3.280840 feet; 39.37008 inches

    1 Mile (statute) - 1.609344 kilometers

    1 Ounce (U.S. fluid) - 1.804688 cubic inches; 29.573730 cubic centimeters

    1 Ounce (avoirdupois) - 28.349523 grams

    1 Ounce (apothecary or troy) - 31.103486 grams

    1 Pint (U.S. liquid) - 0.473163 liter; 473.17647 cubic centimeters

    1 Pound (avoirdupois) - 0.453592 kilogram; 453.59237 grams

    1 Pound (apothecary or troy) - 0.3732417 kilogram, 373.24172 grams

    1 Quart (U.S. dry) - 1.10119 liters

    1 Quart (liquid) - 0.946326 liter

    1 Radian - 57.295779 degrees

    1 Rod - 5.0292 meters

    1 Square Centimeter - 0.155000 square inch

    1 Square Foot - 0.09290304 square meter

    1 Square Inch - 645.16 square millimeters

    1 Square Meter - 10.763910 square feet

    1 Square Yard - 0.836127 square meter

    1 Ton (short) - 907.18474 kilograms

    1 Yard - 0.9144 meter

    POWER - AC CIRCUITS

    Efficiency = 746 x Output HP / Input Watts
    3° KW = Volts x Amps x PF x 1.732 / 1000
    3° Amps = 746 x HP / 1.732 x Eff. x PF
    3° Eff. = 746 x HP / 1.732 x Volts x Amps x PF
    3° PF = Input Watts / Volts x Amps x 1.732
    1° KW = Volts x Amps x PF / 1000
    1° Amps = 746 x HP / Volts x Eff. x PF
    1° Eff. = 746 x HP / Volts x Amps x PF
    1° PF = Input Watts / Volts x Amps
    HP (3°) = Volts x Amps x 1.732 x Eff. x PF / 746
    HP (1°) = Volts x Amps x Eff. x PF / 746
    1 KW = 1000 Watts

    Eff. = Efficiency, PF = Power Factor, KW = Kilowatts, HP = Horsepower



    POWER - DC CIRCUITS

    Torque = HP x 5280 / RPM
    HP = Torque X RPM / 5280
    1 HP = 36 lb.in. @ 1750 RPM
    1 HP = 3 lb. ft. @ 1750 RPM


    Eff. = Efficiency, HP = Horsepower

    OHMS LAW

    Volts (E) = Amps (I) x Ohms (R)
    Amps (I) = Volts (E) / Ohms (R)
    Ohms (R) = Volts (E) / Amps (I)


    R=Ohms, E=Volts, I=Amperes

    To figure miles per hour, multiply the engine RPM by the Wheel Diameter in inches and divide this by the Gear Ratio times 336
    or
    MPH = RPM * wheel diameter (in inches) / gear ratio * 336



    To figure engine speed (RPM), multiply by the Speed in MPH, by the rear axle gear ratio times 336. Divide this by the tire diameter in inches.

    or

    RPM = MPH * gear ratio * 336 / tire diameter


  2. #2
    jdog800's Avatar
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    sorry about the long layout

  3. #3
    jdog800's Avatar
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    This is a little porting software to make the right calculations. You will need excel to make it work.
    Attached Files Attached Files

  4. #4
    just GOT TO DO IT! great lakes gpr 1200's Avatar
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    Talking

    Man That made MY BRAIN HURT just looking at all that info.. It sort of startled my brain. It was all relaxed

  5. #5
    jdog800's Avatar
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    Quote Originally Posted by great lakes gpr 1200 View Post
    Man That made MY BRAIN HURT just looking at all that info.. It sort of startled my brain. It was all relaxed

    The brain is a terrible thing to waste



    Knowing is half the battle.



    Go joe...........

  6. #6
    Mike xsockguyx's Avatar
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    All the equations are simple algebra formula's. Formula's sucks to remember. Thank god for calculators.

  7. #7
    zpeters's Avatar
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    Wow that was some good informationnn..... .For the smartest of all people haha ! Sticky that for the computer geeks! no pon intended!

  8. #8
    Happily Self-Employed WFO's Avatar
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    Quote Originally Posted by great lakes gpr 1200 View Post
    Man That made MY BRAIN HURT just looking at all that info.. It sort of startled my brain. It was all relaxed

    +1

    thank god I have portsmiths to deal with the rithmatic

  9. #9
    WATER WOODY's Avatar
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    Quote Originally Posted by WFO View Post
    +1

    thank god I have portsmiths to deal with the rithmatic
    WERD!

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