re: The "lie" in motor HP *may* be the max HP you can get from the motor before stall (which which would be a lie), which you might very occasionally use. Wouldn't think that would make sense for a shop vac. "
The way I heard it years ago is that the max-claimed HP of a shop-vac, etc. was actually achievable. It was the based on the max amperage the unit would draw if you jammed a screwdriver in the impeller. Just before the motor fried, you will have achieved maximum HP.