
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 / 2 * the square root of A / Vc (L + 1/2 the square root of A
 Vs is the sonic speed Usually 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

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