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01272009, 10:30 PM  #1  
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Formulas, Constants, and Conversions.
Round 2. This is formulas, constants, and conversions. These mainly apply when designing an engine so you know how to safely and properly build it before buying the first part.
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) 2Stroke BMEP = (HP x 6500)/(L x RPM) 4Stroke 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[cos1 (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 exhaustopen 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 / 2¼ * the square root of A / Vc (L + 1/2 the square root of ¼ A Vs is the sonic speed Uusually about 1100 ft/sec) A is the crosssectional 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 lbft = 0.138 kgm = 1.35 Nm 1.00 kgm = 7.23 lbft. = 9.81 Nm 1.00 Nm = 0.102 kgm = 0.737 lbft 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 Temperature F = 9 / 5 x C + 32 C = 5/9 (F  32) K = C + 273.4 Pressure (boost) 1.00 bar = 14.5 psi = 1.02 kg/sqcm = 100 kPa 1.00 psi = 0.069 bar = 0.070 kg/sqcm = 6.89 kPa 1.00 kg/sqcm = 0.980 bar = 14.2 psi = 98.1 kPa 1.00 kPa = 0.010 bar = 0.145 psi = 0.010 kg/sqcm Area / Volume 1.00 sqin = 6.452 sqcm 1.00 sqcm= 0.155 sqin 1.00 cuin = 16.387 cc 1.00 cc = 0.0610 cuin Power 1.00 HP = 746 W torque (lbft) = 5252 x hp / rpm hp = rpm x torque (lbft) / 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 = (Temp32.0) * 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 You can see my other two threads for Engine Formulas and Turbo Mapping as well.
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