The fundamental formula for horsepower sez:

HP = [ (WRN x 2 pi) / 33000 ] Visualize a rope on a windlass arrangement
wound around a shaft of radius "R"; the rope is supporting a load of "W",
and the shaft is turned at a number of revolutions, "RPM"

Whe R = Radius or length of a lever arm about the center of a shaft, in
feet
W = force, weight, in pounds
N = Number of revolutions, RPM

Supposedly, this is the original formula, traceable to James Watt.
Simplifying the formula by dividing out the 2 pi term yields: HP = [ WRN /
5252 ] WR is torque, thus the familiar form becomes: HP = [ (Torque x RPM)
/ 5252 ] or Torque = [ (HP x 5252) / RPM ]

Bob Swinney