JD M Horsepower

[george baker]

20 HP for a JD M but how is it measured? I understand it is different than the way we measure it today. How was the HP established on these older models. Thanks

 

[Brendon-KS]

Up until 1959, the Nebraska tests measured power at the belt pulley and at the drawbar. As the usage of belt power decreased, the power rating was taken at the PTO shaft instead. Since the M was tested in 1947, the report would show belt and drawbar power. The 20hp you mention would be at the belt; drawbar power was around 15.
Belt and PTO power would be basically the same on any given tractor. An exception to this might be the horizontal engine Deeres where the belt pulley was directly connected to the crankshaft and there was no gear train losses; their belt power would probably be higher than what could be measured at the PTO.

 

[george baker]

Thanks, it puzzles me how a machine with 15 to20 horsepower can be so powerful compared with garden tractors today that carry the same rating but are not even close in any respect to these older work horse machines. I used an "economy" tractory when much younger that could not come close but had a similar rating. even my snow blower in the garage is 10 horsepower.

 

[alabamafrog]

There is a difference between horsepower and torque. Torque is why old 20-30 hp Deeres can pull the world.
There is plenty of fancy math involved in the calculating of each.