Google says: http://www.web-cars.com/math/horsepower.html

Below are down to earth barnyard calculations

Todays farmers


.... any suggestions for a caption for the picture below? This great picture is out of the book, Ford Century.

How about this caption,
"The men are late, they must not be catching anything."
Or "Fish always taste so good when camping."

http://www.web-cars.com/math/horsepower.html
"One mechanical horsepower also equals 745.699 watts or .746 kW (kilowatts) of electrical horsepower. This means that if you really want to confuse people, you could complain about the 0.0268 horsepower light bulb your landlord has in the hallway as opposed to the mundane 20 watt measurement."
DJH

Eugene,

Where it really gets intersting is the ALAM horseppower used by early motor car manufacturers. It is a simple calculation based on the number of cylinders, the bore and the stroke. I believe it was just used for determining the license fee - bigger engines cost more.

Two pages from the period provide more information:

1. From Audels:





2. From a book on Auto Repair:




Tom
Detroit

Here is a 20 HP motor running a sawmill.

Tom,

That's simple? I always heard it was one horse pulling a ton (got that from traffic school after getting my 2nd ticket at 16).

Alex

You do it just like you test a pair of LEVI's.

You hitch horses to the rear axle of the car.Then you get in the car and start slowly going forward. If you can move, add horses until you you reach the point where the horses don't back up it's between 20 and 22 horse power. Careful you don't hurt the horses doing this test.
Norm

Norman, Let me complicate the issue. What sized horses should one use to be accurate?
....Michael Pawelek

To add a little to the posting that Dennis supplied. The early steam (and other tractors) had a doule rating. Fo instance a popular Case steam traction engine was the 25-75. It took 25 horses to pull the same size plow. It took 75 horses to do it for 24 hours, (or perhaps that was for 8-10 hours).
I had a 1915 Case 65. This was it's drawbar rating at 2 1/2 mph. 22 horses could pull the same size plow. It would produce 105 hp on the belt pulley. It took 40 hp just to move it's 14 tons across a farm field. It was exceedingly inefficient when it came to converting fuel to usefull work, about 3%, the rest was mostly lost heat and a little friction.