Horse power???

There's probably some variables but maybe it's just a simple answer.
Never gave it any thought until I was looking at the specs for my tractor and a couple others that share the same motor. They are rated at 24 and 26 HP. the 2 with 24HP have a different trans than the 26HP. Mine shows 24 on the specs (web) but has the same trans as the 26 HP. Is it the motor only, or does gearing make the difference also?

Just curious.

Dave

Well,

if you mean what is the difference in the engines, same block with different pump settings and governor will give different horsepower. More fuel- more rpms- more power.

if you are asking, does gearing give you more horsepower, then no, it only transforms what the engine makes into usable power (the ability to turn the tires or run the belt). Hope that makes sense.

(quoted from post at 04:04:40 11/14/09) Well,

if you mean what is the difference in the engines, same block with different pump settings and governor will give different horsepower. More fuel- more rpms- more power.

if you are asking, does gearing give you more horsepower, then no, it only transforms what the engine makes into usable power (the ability to turn the tires or run the belt). Hope that makes sense.

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they each list the HP @1900 RPM's. just figured more fuel would flood the system. If that's all it is, you'd think that they'd have just set the pumps for max HP and been done. guess that's how they sold the next model as new and improved w/ the same equipment......

Dave

The transmission must be able to handle the engine torque, not necessarily the horsepower. Power equals torque times RPM. Now you can't increase horsepower by changing the gearing, because you won't have more horsepower than what you started out with: As you increase the torque through transmission gearing you reduce the RPM and horsepower stays the same (minus friction loss).

HOWEVER, tractors are normally rated at the PTO at 540 RPM. So, if you have two tractors that have the identical engine, and tractor A produces 540 PTO RPM at 2300 engine RPM, and tractor B produces 540 PTO RPM at 2100 engine RPM, tractor A will have a higher PTO horsepower rating than tractor B. Even though the engines are identical, tractor A produces greater PTO horsepower at the rated rpm.

Another thing to consider is that it doesn't take much of a modification for an engine to generate a bit more horsepower. Different carburetors or injectors, different cam timing, compression ratio or governor settings can be used to squeeze a bit more power out of an engine. Back in my yachting days, I owned a 120 HP Evinrude outboard motor. Looking through the parts breakdown, I found that the only difference between the 120 and 140 horsepower motors was the carburetor bodies. Of course, OMC charges several hundred dollars more for the 140 HP motor, even though it doesn't cost them a nickel more to produce than the 120.

Dave:

PTO HP is significantly less than engine flywheel HP due to losses in the transmission, etc. Tractors with identical engines often produce different power outputs at the PTO when equipped with different transmissions.

Hydrostatic transmissions are extraordinarily inefficient, often turning 25% or more of the engines power into heat. Such is the price of convenience.

Dean

There are many variables when a company posts horsepower ratings. Besides what has already been mentioned, there is the issue of longevity. Some makers post absolute max. horsepower that an engine cannot sustain very long before it wears out. Very common in cars and pickkup trucks. Other makers post horsepower that an engine can produce for a long time without suffering too bad. So, sometimes you can take the same engines - and one will be listed as 200 horsepower in light-duty use and same engine in a heavy duty rig listed at only 100 horsepower.

In North America the SAE HP net rating at the pto or drawbar.
The European HP rating are gross ratings at the flywheel. Without driveline losses, hydraulic pump(s), alternator, cooling fan etc.
Rough ballpark numbers of 1% loss at every gear to gear step.

IH in Germany used the European DIN horsepower rating for their tractors up to 1962 than switched to SAE horsepower rating (which raised the apparent horsepower ratings). The earlier D-214 tractor, 2 cylinder 14 HP (DIN) became the D-215, 2 cylinder 15 HP (SAE). The D-324, 3 cylinder 24 HP (DIN) became the D-326, 3 cylinder 26 HP (SAE). The only other changes where the earlier wheels were red with white rims whereas the later tractors initially came out with all white wheels.

(quoted from post at 16:49:18 11/14/09) IH in Germany used the European DIN horsepower rating for their tractors up to 1962 than switched to SAE horsepower rating (which raised the apparent horsepower ratings). The earlier D-214 tractor, 2 cylinder 14 HP (DIN) became the D-215, 2 cylinder 15 HP (SAE). The D-324, 3 cylinder 24 HP (DIN) became the D-326, 3 cylinder 26 HP (SAE). The only other changes where the earlier wheels were red with white rims whereas the later tractors initially came out with all white wheels.

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Thanks to everyone, but this is something a thick headed guy like me can pick up on quick and talk about it like an expert :shock:

Thanks, Dave