Does HP matter?

[MARKMILES77]

If two tractors have identical peak torque but one has more power than the other is there any point in getting the tractor with more horsepower?
For example the JD 3032E has 31.4 Hp while the JD 3038E has 37 HP but they have identical peak torque.
Are those extra horses useless?
I would have thought that for heavy work like rotary cutting thick scrub that the extra horses would not help?


Mark

[mjncad]

Ask a woman if size matters.

Seriously now, do the peak torque and HP numbers occur at the same RPM's between the engines? If the extra HP's don't cost a lot extra, I'd go with the 37HP unit as it in theory will get you an extra foot of brush-cutter width using the rule-of-thumb of 5HP per 1-foot of brush-cutter width.

[creekbend]

There is a difference of five-5 HP - PTO in those two models. TractorData.com - information on all makes and models of tractors

[JD 4520]

Get more HP if you can. You won't later regret it.

[KennyG]

Torque is a measure of force while horsepower is a measure of work done so, yes, higher horsepower is useful. If two engines have the same torque but one has higher horsepower, it means the higher powered one will develop that torque at a higher engine speed and do more work. In the case identified above, different causes could exist, but if both are geared to produce maximum power at the PTO speed, the higher horsepower tractor will put more energy into the driven device and do more work.

The only case in which this wouldn't work is if both tractors have the same gearing and the higher horsepower tractor only produces the greater horsepower beyond the PTO speed, in which case the extra power can't be used when using a PTO powered implement.

If you look at tractors, you will find that PTO horsepower is almost always less than engine horsepower. Theres a bit of drivetrain loss but most of that is because the torque curve is very flat and the engine will rev somewhat past the PTO rated speed.

[bcp]

Depends if you are pulling or powering, too.

A heavier tractor with a smaller engine will often outpull a lighter one with a larger engine. Weight makes traction, horsepower lets you run bigger powered implements or do the work faster.

Bruce

[EE_Bota]

Horsepower is work per unit time. Work/per hour, etc. All things being equal, I'd go for the higher horsepower. But I don't say that lightly. You supplied an important point: the torque is equal. But you didn't say what your travel speed limitations are...so I presume low range low gear will be slow enough for you on both tractors.

The reason it matters is motors always have to be coordinated with gear box ratios. These modify the torque and the speed, and you'd be surprised how many situations I have walked up on in an industrial environment where folks choose a certain HP first because they have a rule of thumb about how much power a machine will take. Then, they meet with production people who ask for extremely fast speeds so the engineer just changes the gearbox ratio and then purchases the machine. Then in production at normal speeds, the device doesn't have the final torque to run the process, but unloaded it can run fast as heck! It's disheartening when I see that happen, but I doubt it will happen with your tractor choices.

[hodge]

Dollars to donuts the torque peak is at different RPM's between the two engines. HP and torque numbers are only part of the equation; where in the RPM range that they happen is important, too.

[murphy1244]

Dollars to donuts the torque peak is at different RPM's between the two engines. HP and torque numbers are only part of the equation; where in the RPM range that they happen is important, too.

Good advice, I would take the machine that peaks at a lower RPM assuming same same.

[KennyG]

Good advice, I would take the machine that peaks at a lower RPM assuming same same.

But the original question was about bushhogging. For that application you would want the machine with the highest PTO horsepower since you will be running at the PTO rated RPM.