In a Honda research center in Japan, the highest four-stroke RPM where able to explore was 26,000rpm. This was back in 1964.
19,000rpm for the highest service peak-power RPM reached by Honda’s NR500 four-stroke GP engine, this was in 1982…
And if we about RPM numbers the first recorded four-stroke engine from Nikolaus Otto had 180rpm for its four-stroke internal combustion engine in 1876.
What is the highest rpm for a four-stroke engine ever reached?