Formulas

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"

Way cool .... thanks!

That is VERY cool stuff. Saved it to file for future use!

kzz1p wrote:

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.

Umm, seems to be a typo there (marked in red), I believe the last line should just read:

Torque = (100 x 5252) / 4000 = 131 ft-lbs.

Scotch and soda = scotch x 2 and soda.

Bluemeanie wrote:

That is VERY cool stuff. Saved it to file for future use!

Saving to file won't be necessary, as OMR will soon be posting all the charts. :laugh: :laugh:

Good Luck!

Patton wrote:

Bluemeanie wrote:

That is VERY cool stuff. Saved it to file for future use!

Saving to file won't be necessary, as OMR will soon be posting all the charts. :laugh: :laugh:

Good Luck!

Only if he can polish them to a mirror like finish first :blink: :silly: :silly: :blink:

OnkelB wrote:

kzz1p wrote:

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.

It could be, I'm not a Math guy!



Umm, seems to be a typo there (marked in red), I believe the last line should just read:

Torque = (100 x 5252) / 4000 = 131 ft-lbs.

you guys think way too hard! :laugh:
Big bore x short stroke + right cam and carbs with a good head = lots of power!
:woohoo:

PLUMMEN wrote:

you guys think way too hard! :laugh:
Big bore x short stroke + right cam and carbs with good head = lots of power!

:woohoo:

You got it going on there Fred, er I mean Jim.:laugh:

Bill

Nothing wrong with good head. Thats a winning formula !