Unfortunately, that claim was on the packaging which is long since gone. The rating plate on the vacuum says 10.4 amps/120 volt, which would work out to 1.67hp input (that may include the power to the brush motor and light as well)
However, I did buy a new Shop Vac this year with a label in plain sight that proclaims 4.5 peak hp and the rating plate says 9 amps/120 volt. which works out to 1.44 hp input. At 75% efficiency, this would be about a 1 hp motor. I have to say, though, it is the most powerful vacuum that I have ever owned.
As the excerpt I quoted in post #6 explains, vacuum cleaner claims of peak hp are based on a totally unrealistic method of measurement done strictly for marketing purposes and no real indication as to how well the vacuum cleaner will perform.
The point being, though, that you can't trust advertising claims when looking at expected performance. A modern motor may look like an economical replacement for your tired old motor but you may be disappointed with the outcome. If you calculate the horsepower by the rated input power (volts x amps), you may have a better understanding of what to expect. Factor in for efficiency and if the labling says anything like peak, figure a sizable factor for that as well.