Built for low RPM torque for sure. What RPM they ran at I do not know. I would figure more like 2,500 RPM to 3,000 RPM. Then they ran at or close to wide open throttle and high load. Not many days of running in a year but long days when they did. By the time the combine was retired it was usually the threshing components that were really worn. But the engine rings and bearings would take a beating.
