RPM (piston speed, stroke)

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Equation / Last modified by KurtHeckman on 2018/02/13 21:05
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KurtHeckman.RPM (piston speed, stroke)
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1f0e355d-b3b7-11e4-a9fb-bc764e2038f2

The Engine RPMs calculator computes the revolutions per minute (RPMS) based on the average (mean) speed of the pistons, and the stroke length.piston rev.pngOne rev 

INSTRUCTIONS: Choose units and enter the following:

  • (pS)  Mean Piston Speed
  • (s) Stroke Length

Engine RPMs: The calculator returns the engines RPMs.

The Math

The equation for the RPMs of an engine is as follows:

            `RPMs = (ps)/(s*2)`

The Piston Speed equation calculates the mean velocity of the piston based on the cylinder stroke length and the RPMs.  The piston's speed of travel up and down the cylinder is always changing and actually comes to an instantaneous stop at both the upper and lower ends of the stroke at the beginning and end of a single revolution.  Therefor we can only calculate the average (mean) velocity based on RPMs.  In one minute, the pistons travel two times the stroke length times the number of revolutions (2 * Stroke * Revs).  Divide that by one minute and you have the mean piston speed.

   Inch Equivalences
FractionDecimalMils
1/16th0.062562.5
1/32th0.0312531.25
1/64th0.01562515.625

Related Combustion Engine Calculators: 

  • RATIOS AND LENGTHS:
    • Bore (diameter): Compute the Bore Diameter based on the engine displacement, number of cylinders and the stroke length.
    • Bore Stroke Ratio: Compute the Bore Stroke Ratio based on the diameter of the bore and the length of the stroke.
    • Compression Ratio: Compute the Combustion Ratio base on the minimum and maximum displacements of the cylinder at the beginning (1-Induction) and compressed (3-Power) portions of the combustion cycle (see animation)
    • Displacement Ratio: Compute the Displacement Ratio based on the volumes at the beginning and end of the stroke.
    • Rod Length Stroke Ratio: Compute the Rod and Stroke Length Ratio base on the two lengths.
    • Stroke (length): Compute the Stroke Length based on the total engine displacement, number of cylinders and the bore.
  • VOLUMES:
    • Total Engine Displacement: Compute the Total Volume (displacement) of a Combustion Engine based on the bore, stroke and number of cylinders.
    • Engine Cylinder Volume: Compute the Volume (displacement) of a Engine Cylinder based on the bore and stroke.
    • Engine Cylinder Overbore Volume: Compute the Volume (displacement) of an Engine with an Overbore based on the stroke, bore, overbore and number of cylinders.
    • Rotary Engine Equivalent Displacement: Compute the Equivalent Volume of a Rotary Engine based on the swept volume and number of pistons.
    • Compression Volume (V2): Compute the Compressed Volume of a Cylinder when the piston is at the end of the stroke and the chamber is at its smallest (and most compressed) volume, based on the chamber, deck, crevice, chamfer, gasket, valve relief and dome/dish volumes.  This is the second volume (V2) in the Compression Ratio calculation.
    • Gasket Volume: Compute the Volume of a Gasket based on the inner and outer diameters and the gasket's thickness.
    • Deck Volume: Compute the Volume of a Cylinder Deck based on the deck height and the bore.
    • Crevice Volume: Compute the Volume of a Cylinder Crevice based on the piston diameter, cylinder bore and the crevice height.
    • Chamfer Volume: Compute the Volume of a Cylinder Chamfer based on the cylinder diameter and the chamfer height and width.
  • SPEEDS AND RPMS:
    • Piston Speed: Piston Speed (mean) based on stroke length and RPMs.
    • Max Piston Speed: Max Piston Speed based on stroke length and RPMs