Just do what everybody else does- - - - -lie about it! To get an accurate reading, you'll need a dyno.

Horsepower = torque X RPM divided by 5250.

Then you'll need to dial in a correction for ambient temperature and humidity. On average, the correction factor reduces the raw HP figure by 5 to 7 percent. There's a computer simulation program called "Desktop Dyno" that seems to be pretty accurate. I've done a few fantasy engine builds with D/D on small block Chevy engines, using the same parts specifications as ones I've actually built and dyno'ed, and the numbers came out close to equal for the real thing and the computer simulation.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!