I have a whirlpool thin twin in my shop right now- a DD. The label says they spin at 640 rpm.

Did the old belt drive machines (the compact/portables) spin at something like 800 rpm. I don't remember

Interesting. Never knew the spin speed on a DD before; I wonder if the full-sized versions spun at 640 as well.

The early WP/KM BD portables (late 60's??) were 24" full-sized machines in a portable cabinet, with a single-inlet water valve (no temperature control) and retractible wheels. They had a large 12 lb. tub, and spun at 525. Not sure what the speed was on the later, smaller models, but I know it was fast. The earlier version seemed more practical; not sure why Sears/Whirlpool discontinued it. I've seen the "small" BD portables and the tubs appeared quite dinky. Same with the DD models and ThinTwins. One of our members has a full-sized Kenmore portable, but I don't remember who.

As a sidenote, I was looking at the underside of my GE (Hitachi) portable and, aside from a larger pulley that drives the impeller connected to a smaller motor pulley, there was virtually no reduction gearing for the tub. A monster solenoid energizes, pulls out the clutch arm, and off it goes, spinning at the same speed as the impeller during the wash cycle! No wonder it made a "Wa-wa-wa-wa-wa-wa-wa-wa-wa-wa" sound as the motor picked up speed!

This is interesting!
Yes Kenmore (two shirt) extra small portable has a very high spin speed and as for my Kenmore/Whirlpool standard portables (which holds at least 15 or more shirts) spun only at 525RPM....

And it it a fact that the BD version spun much faster than the DD version. I have both in the cellar and the BD needs a tranny overhaul....