Engineers compare mean and peak piston speeds easily. Choose units, angles, and rod length quickly. Validate designs with clear tables and downloadable outputs today.
Mean piston speed is computed from stroke and rotational speed:
Ū = 2 × Stroke × RPM / 60
where Stroke is in meters and RPM is revolutions per minute.
Approximate peak speed (SHM) is a fast estimate when rod length is unknown:
Vmax≈ = π × Stroke × RPM / 60
Exact speed uses slider-crank geometry with connecting rod length L and crank radius R=Stroke/2.
Displacement from TDC is:
s(θ) = (R+L) − (R cosθ + √(L² − (R sinθ)²)).
Velocity is obtained from v(θ)=ω·ds/dθ, and acceleration from a(θ)=ω²·d²s/dθ².
| RPM | Mean Speed (m/s) | Exact Peak Speed (m/s) | Peak Angle (deg) |
|---|---|---|---|
| 1500 | 4.3000 | 7.0552 | 74.5 |
| 3000 | 8.6000 | 14.1105 | 74.5 |
| 6000 | 17.2000 | 28.2210 | 74.5 |
Mean piston speed (Ū) compares engines by linking stroke and RPM into one value. Many durable production designs operate near 10–15 m/s, while high‑output layouts often approach 18–22 m/s. Lower values generally reduce ring sliding speed and oil film stress at the liner. For the sample 86 mm stroke at 3000 rpm, Ū is 8.6 m/s, indicating margin for long service.
Peak piston speed occurs before and after mid‑stroke, not exactly at 90°. A quick estimate uses simple harmonic motion, giving Vmax≈ = (π/2)·Ū. Exact peak depends on rod ratio L/R; lower ratios increase peak speed and shift the peak angle toward the power stroke. Typical passenger designs sit around L/R = 3.0–4.5. With a 143 mm rod and 43 mm crank radius, L/R ≈ 3.33 and the exact peak speed is about 14.11 m/s near 74.5° at 3000 rpm.
Stress and bearing loads track acceleration more than mean speed. Acceleration rises with ω², so doubling RPM roughly quadruples inertial loading. Using the same 86/143 mm geometry, peak acceleration is about 5,520 m/s² at 3000 rpm and about 22,080 m/s² at 6000 rpm, roughly 2,252 g. These values help size pins, rods, and fasteners, and they support fatigue checks when combined with reciprocating mass.
The angle table converts crank degrees into displacement, velocity, and acceleration snapshots. This helps align valve events, injection timing, or ignition targets with piston motion rather than just crank position. Smaller steps (5–10°) improve resolution around TDC where acceleration and dwell change rapidly, while larger steps (15–30°) are sufficient for quick comparisons. Reviewing 0–360° provides a full cycle for timing discussions.
Design reviews require consistent units and repeatable calculations. Exporting to CSV supports analysis in spreadsheets, plotting speed versus angle, and archiving parameter sets alongside test data. The PDF report provides a one‑page summary for sign‑off or maintenance documentation, keeping inputs, key speeds, and notes together. Recording tolerances for stroke, rod length, and RPM helps bound the expected speed range.
It calculates mean piston speed from stroke and RPM, estimates peak speed using a quick harmonic approximation, and computes exact speed, displacement, and acceleration when connecting rod length is provided.
Mean speed depends only on stroke and RPM. Exact peak speed, peak acceleration, and instantaneous values come from slider‑crank geometry, which needs rod length to resolve the changing connecting‑rod angle.
Rod ratio is connecting‑rod length divided by crank radius (stroke/2). Higher ratios reduce side thrust and make motion closer to simple harmonic. Lower ratios increase peak speed and shift the peak away from mid‑stroke.
Peak acceleration is the strongest inertial loading point, typically near TDC or BDC. It scales with RPM squared, so small RPM increases can raise loads sharply. Use it for pin, rod, and fastener checks.
Use 5–10° for detailed timing and near‑TDC behavior, 15° for general comparisons, and 30° for quick screening. Smaller steps increase rows and export size but improve resolution.
No. Exports are generated from your most recent calculation stored only for the current session. Run a new calculation to update the export contents, then download the updated CSV or PDF.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.