Formulas

 

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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