Following are some of the
most commonly used formulas useful for high
performance work.
Displacement from Bore and Stroke
displacement = pi
x (radius squared) x height
example: 4 inch
bore, 4 inch stroke
displacement =
3.14159 x (2 squared) x 4 = 50.265ci per cylinder
Cubic Centimeters from Cubic Inches
cc = (2.54 cubed)
x ci
example: 100ci
cc = (2.54 cubed)
x 100 = 1638.7cc
Cubic Inches from Cubic Centimeters
ci = cc / (2.54
cubed)
example: 1200cc
ci = 1200 / (2.54
cubed) = 73.23ci
Horsepower from Torque and RPM
hp = (torque x
rpm) / 5252
example: 80 ft-lbs
at 4000 rpm
hp = (80 x 4000) /
5252 = 60.93hp
Torque from Horsepower and RPM
torque = (hp x
5252) / rpm
example: 100hp at
4000 rpm
torque = (100 x
5252) / 4000 = 80 x 4000) / 5252 = 131 ft-lbs.
Average Piston Speed from Stroke and RPM
average piston
speed in fpm = (stroke in inches x rpm) / 6
example: 4 inch
stroke at 6000rpm
aps = (4 x
6000) / 6 = 4000 feet per minute
Horsepower from Quarter Mile Speed and Weight
hp = ((mph / 223)
cubed) x weight
example: 130 mph
with a 600lb bike & rider weight
hp = ((130 / 223)
cubed) x 600 = 118.8 hp
Horsepower from Elapsed Time and Weight
hp = weight / ((ET
/ 5.92) cubed)
example: 10
seconds ET with a 600lb bike & rider weight
hp = 600 / ((10 /
5.92) cubed) = 124.5 hp
Elapsed Time from Horsepower and Weight
ET = 5.92 x cube
root of (weight / horsepower)
example: 650lb
bike with 140hp
ET = 5.92 x cube
root of (650 / 140) = 9.88 seconds
Quarter Mile Speed from Horsepower and Weight
mph = 223 x cube
root of (horsepower / weight)
example: 650lb
bike with 140hp
mph = 223 x cube
root of (140 / 650) = 133.67mph
Elapsed Time from Quarter Mile Speed
ET = (1320 / mph)
example: 10 second
bike
ET = (1320 / 10) =
132 mph
Quarter Mile Speed from Elapsed Time
mph = (1320 / ET)
example: 134 mph
bike
mph = (1320 / 134)
= 9.85 seconds
Flow Bench Test Pressure Conversion
Flow = (square
root of (new flow pressure / known flow pressure)) x
known cfm
example: 160 cfm @
10", convert to 28"
Flow = (square
root of (28 / 10)) x 160 = 267.7 cfm at 28"
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