Piston RPM Help

Where:
RPM = Revolutions Per Minute

A piston's RPM is the amount of revolutions it makes in one minute. This is found by dividing six times the speed of the piston (in feet per minute) by its stroke (in inches.)

Speed of Piston
The speed of a piston is how fast it rotates around its cylinder. This is measured by how many feet it travels every minute.

This speed is multiplied by 12 to keep track of units. Since in our equation piston speed is in feet per minute and stroke is in inches, we must bring piston speed to inches per minute so that its units can divide into the units of the stroke. There are 12 inches in a foot, so to bring piston speed to inches, we multiply it by 12.

Stroke of Piston
The stroke of a piston is the distance it travels around its cylinder in one revolution. Obviously, this value relies greatly on wide around the piston's cylinder is.

Since in one revolution, the piston goes up and then comes back down, this is multiplied by 2 to compensate for the two movements that make up one revolution.

Example 1
A piston's stroke is 2.75 inches. It travels at 2,575 feet per minute. Find its RPM.

The piston travels at 5,618.18... revolutions per minute.

Works Cited

Lumley, John. "The Star Sapphire Engine." ASOC. 29 June 2001. Armstrong Siddeley
     Owners Club Ltd. 10 July 2006.
     <http://www.siddeley.com/info_sapphire_eng.html>.

Mullen, Stephen. "Here Are the Formulas for Calculating Motorcycle and Automotive
     Performance." Nightrider.com. 2006. Stephen Mullen. 10 July 2006.
     <http://www.nightrider.com/biketech/calc_formulas_page.htm>.

Steve W. "Calculating Maximum RPM Limits." Mustangs and More.com. 1999. Steve
     LaRiviere. 10 July 2006.
     <http://www.mustangsandmore.com/ubb/SteveWmaxpistonspeed.html>.

"Formulas." RPMoutlet.com. 2003. RPM Outlet Inc. 10 July 2006.
     <http://www.rpmoutlet.com/formula.htm>.