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Piston speed
The mean piston speed says more about the load on the rotating assembly than the rpm alone. Enter the stroke and rpm and you see where you stand against known limits.
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Mean piston speed
17,3 m/s
Mean piston speed. Street engines normally sit under 18 m/s, race engines around 20-25 m/s.
How the calculation works
The piston moves two strokes per revolution, down and up. The distance per minute is thus 2 times the stroke times the rpm. Converted to metres per second it is 2 × stroke × rpm divided by 60000. That is the mean speed, the peak speed mid-stroke is considerably higher.
Two engines can rev equally high but load the rotating assembly quite differently. A long-stroke engine reaches its limit at lower rpm than a short-stroke one. High piston speeds require forged pistons, good lubrication and a rotating assembly that withstands the load.
Example
An engine with an 80 mm stroke revving to 6500 gives a mean piston speed of 17,3 m/s, which is on the high side for a street engine.
Safe mean piston speed
| Engine type | Mean piston speed |
|---|---|
| Street engines | 16-18 m/s |
| Race engines | 20-25 m/s |
| Pro Stock | 30-33 m/s |
| Formula 1 | 25-28 m/s |
| Diesel engines | 8-15 m/s |
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