The FD Pulsamatic Washer
Was designed to lower production costs by only having one speed reduction form a normal US induction motor speed of 1750 RPMs, this is why it spun at 660 RPMs and agitated at 660 pulses per minute.
FD only tried this once and only for a few years, after the unimatic design was dropped for home machines they added a 2nd second belt and set of pulleys so the agitation speed could return to 330 PPM where it stayed through several more mechanism designs till FD stopped making washers around 1980.
Other washer builders over the years used the same cost reduction in their washers design, The Philco Automagic is another.
More modern examples are the WP DD washers and the Maytag helical drive washers with the orbital transmissions.
All these designs had a faster agitation rate with a shorted stroke, it has been hotly argued over on this site whether this was a good idea or not.
John