Most of the high RPM noise comes from the fan. Stovebolt engines in general were designed to run all day, every day at 3K+ RPM, and the 261 has a heavier duty lower end than either a 235 or a 216. It was intended to power medium duty trucks with heavy loads, usually running up against a governor for hours at a time. Most people are too timid to work a stovebolt the way it was intended to be used. 3200-3600 RPM was where they developed their maximum horsepower, and they will still do that if the rod bearing clearance and oil pressure is right.
Jerry
