Horsepower is a measure of power in the mechanical world much like watts is a measure of power in the electrical world. Horsepower is the product of torque and rpm. Torque is the twisting force and the rpm, how rapidly you can perform this twisting force, determines the power (horsepower). If you lift 550 pounds 1 foot in 1 second you have produced 1 horsepower. If you have a model airplane engine that turns at 10,000 rpm and with suitable gearing it is coupled to a winch and it manages to raise 550 lbs, 1 foot, in 1 second it produced at least 1 horsepower (more, unless you have a no friction perfect gearbox on your winch). A 1725 rpm electrical motor again with suitable gearing connected to the winch lifting 550 lbs, 1 foot, in 1 second also produces 1 horsepower. Obviously torque from the model airplane engine is much lower than the torque on the electric motor, much like the difference between the 20+ hp lawn tractor engine and the 20+ hp compact tractor.
Then there are muddling factors like gross hp ratings vs net hp ratings. The garden tractor manufacturer may have quoted a gross hp output at the flywheel, where as the FEL may have quoted net hp at the draw bar or PTO. It was this marketing nonsense and liberties that created the Nebraska testing laboratory in the early days of ag tractor manufacturing. Add to that the durability factor i.e. how long can that engine generate that 20+ hp and not self destruct, and things get rather confusing.
As a kid growing up we would see that the Chevy 283 V8 was rated at a 195 hp. Yet my dad's 400 cubic inch IH 856 was only 100 hp. What's up with that? One thing, the rpm at which those horsepower outputs had occurred, another how long can you keep that up?
Yes I am sure that the 283 V8 installed in a tractor suitably geared to the transmission would indeed pull 100 possibly 150 horsepower but I daresay that a few days of pulling the field cultivator would leave you with a smoking ruin of an engine, as sustaining the power output to put a 100+ draw bar horsepower on the field cultivator would overstress pistons, valves, etc. to point of failure. If you ballasted the 20+ hp garden tractor sufficiently you could pull that scaled down land plane almost as well as the 20+ hp Kabota. But the Kabota will be doing it long after the garden tractor shucked a rod or blew a transmission.
gordon
