A reciprocating piston engine links piston motion to crankshaft rotation. This calculator evaluates geometric swept displacement and simple rate conversions for an explicitly assumed four-stroke cycle; it is not an engine-performance model.
Vertical Gasoline Engine Interactive Calculator
Enter crankshaft speed, cylinder bore, piston stroke and cylinder count. Results are ideal geometry and rate conversions under a four-stroke assumption, not predictions of torque, power, fuel use or engine capacity.
Equation Used
- The operating-cycle convention is four stroke: intake, compression, power and exhaust.
- Each cylinder has one power event per two crankshaft revolutions.
- Bore and stroke are ideal geometric dimensions shared by every entered cylinder.
- Total displacement is the swept volume of all entered cylinders.
- Mean piston speed is 2 times stroke times crank revolutions per second.
- Compression ratio, clearance volume, connecting-rod length, valve timing, combustion, pressure, torque, power, efficiency, fuel use, heat transfer, friction, inertia, balance, stress, cooling, lubrication, emissions and safety are omitted.
Four-Stroke Geometry and Rates
The FAA describes the four separate piston strokes as intake, compression, power and exhaust. NASA defines bore as cylinder diameter, stroke as piston travel, and total displacement as the sum of all cylinder swept volumes. The animation shows that topology; its chosen connecting-rod proportion is illustrative.
What This Calculator Represents
The tool converts entered rpm to revolutions per second, counts one assumed power event per cylinder per two revolutions, calculates circular swept volume from bore and stroke, and reports the geometric mean piston speed.
Ideal Four-Stroke Arithmetic
events/s=cN/120
Vd=pi B^2 S c/4
mean piston speed=2Sn
B and S are converted consistently so displacement is reported in cubic centimetres and piston speed in metres per second.
Worked Idealized Example
For 3,000 rpm, 70 mm bore, 75 mm stroke and one cylinder, crankshaft rate is 50.0 rev/s, assumed four-stroke event rate is 25.0 events/s, total geometric displacement is about 288.6 cc and geometric mean piston speed is 7.50 m/s.
Model Boundary
- Calculated: shaft rate, assumed four-stroke event rate, swept displacement and mean piston speed.
- Illustrated: one piston, connecting rod and crank moving through the four named strokes.
- Not calculated: clearance or compression ratio, exact rod geometry, valve timing, pressure, torque, power, efficiency, fuel consumption, temperatures, loads, vibration, stress, durability or safety.
Frequently Asked Questions
Does this calculate engine power?
No.
Why divide rpm by 120 for events per cylinder?
A four-stroke cycle takes two crankshaft revolutions. At N rpm, each cylinder has N/2 power events per minute, or N/120 per second.
Is displacement combustion-chamber volume?
No; it is geometric swept volume.
Is mean piston speed instantaneous piston speed?
No; it is total stroke travel per unit time.
Does the drawing use an entered connecting-rod length?
No; its rod proportion is illustrative and does not affect results.
Can this size or rate an engine?
No.
References
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