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Car Engineering Information

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Car Engineering Information

Postby Audacity Racing » Mon Feb 06, 2006 2:36 pm

Estimated Power:
BHP = PLAN/33,000
where:
P = BMEP, in PSI
L = piston stroke, measured in feet
A = Area of one piston, in square inches
N = Number of power strokes per minute

BMEP(Brake Mean Effective Pressure)
BMEP = (HP*13000)/(L*RPM)
Where:
HP = Horsepower
L = Displacement in Liters(1 ci. = 16.39 cc = .01639L)

Rod/Stroke Ratio:
A = L/S
Where
L = Rod Length (in inches)
S = Stroke (in inches)

Piston Acceleration:
Gmax = ((N^2*L)/2189)(1+1/(2A))
Where:
Gmax = max. piston acceleration, in feet/sec squared
N = Crankshaft speed, in RPM
L = stroke, in inches
A = Rod Ratio

Piston Travel vs. Crank Rotation:
d = ((S/2)+L)-(S/2 cos X) - L sin [cos-1(S/2L sin X)]
WHere:
S = Stroke (mm)
L = Rod Length (mm)
X = Crank Angle before of after TDC (in degrees)

Piston Speed:
Cm = .166*LN
Where:
Cm = Mean piston speed, in feet per minute
L = Stroke (in inches)
N = Crankshaft speed (RPM)

Piston Stroke Motion:
S = (R cos X)+(L cos Z)
Where:
S = Distance of piston wrist pin from center of crankshaft
R = Radius of wrist pin
L = Length of Rod
X = Angle of wrist pin
Z = Angle of the rod

Compression Ratio:
CR = (V1+V2)/V2
Where:
CR = Compression ratio
V1 = Cylinder volume at exhaust closing
V2 = Combustion Chamber volume

Port Open Time:
T = (60/N)(Z/360)
Where:
T = Time in seconds
N = Crankshaft Speed (RPM)
Z = Port open duration, in degrees

MPH Calculate:
MPH = (RPM*D)/(R*336)
Where:
RPM = Engine RPM
D = Wheel Diameter (in inches)
R = Gear Ratio

RPM Calculate:
RPM = (MPH*R*336)/D
Where:
MPH = Speed
R = Gear Ratio
D = Tire Diameter (in inches)





Here's a few more - these will allow you to compute the compression ratio of an engine:

CR = (V1 + V2)/V2
Where:
CR = Compression Ratio
V1 = Cylinder Volume (in cubic centimeters (cc))
V2 = Cylinder Head Volume (in cubic centimeters (cc))

V1 = (B^2 * (pi/4) * S)/1000
Where:
B = Bore (in mm)
pi = 3.1416
S = Stroke (in mm)

V2 = HV + DV + V3
Where:
HV = Cylinder Chamber Volume (in cubic centimeters (cc))
DV = Piston Dish Volume (in cubic centimeters (cc))
V3 = Slice (or Squish) Volume (in cubic centimeters (cc))

V3 = B^2 * (pi/4) * (G - DC)
Where:
G = Head Gasket Thickness (crushed) (in mm)
DC = Deck Clearance (in mm)

Formula for Engine Displacement:
D = (B^2 * S * (pi/4))*n
Where
D = Engine Displacement (in cc)
B = Cylinder Bore (in mm)
S = Stroke (in mm)
n = number of cylinders

Formulas for brake horsepower

Horsepower:
HP = rpm x T / 5252
Where:
HP = Horsepower
RPM = Engine speed (RPM)
T = Engine Torque (in lb*ft)
Torque:
T = 5252 x horsepower / rpm
ALSO - HP = Torque (Nm) x RPM / 7120.6616


Brake Specific Fuel Consumption
BSFC = F / BHP
Where:
F = Fuel (lbs/hr)
BHP = Brake Horsepower

BHP loss based on elevation:
L = E/1000 * 0.03 * BHP
Where:
L = BHP loss
E = elevation in feet
BHP = BHP at sea level
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