On the issue of hp

[Anonymous Poster]

I am curious if anyone knows why tractors are rated by their hp numbers instead of the engine torque numbers. I may be just as wrong as I can be but isn't torque what makes a tractor more or less capable? I know say for instance on a pickup, you can have all the hp you want,but with out torque you're not going to do any towing or other "work" with it. I know that while more hp = more mph, torque is what determines how quickly you get up to that mph. I have not been able to find torque numbers for any of the tractors I'm considering. It may not be an important issue ( or even a good way to rate), but I'd still like to know the numbers on these tractors simply out of curiosity. I know by the nature of the motors that the torque is more than likely twice the rated hp. So far I'm guessing maybe this factor is common knowledge or something which is why it's not addressed. Any and all answers welcome.They say the only dumb question is the one left unasked.

 

[thcri]

Leadfoot,

I believe you have opened a thread that will last forever? It is a good question and I haven't been around TBN long enough to know if it was asked earlier. But I would be willing to bet that it was addressed someplace before. There is so many ways to address HP and torque that I think it could make ones head spin. Torque gets you to a point, HP keeps you there. IE: gas engine from a dead start will whale on a diesel HP for HP. But fully loaded going up a steep hill the diesel with less torque and same HP will maintain speed much better. In another thread there was discussion on a couple of new John Deere's and one should buy the smaller HP one because it had more torque than the larger one??? If I understood that one right I am not so sure I would go for the smaller one. To me more Horsepower is always better. After you pick your HP then I would then divide the tractors your searching for my torque.

This is one thread I will watch and add to my favorites as I would like to learn more on it.

murph

 

[timb]

Leadfoot - bigger tractors are rated typically by their PTO horsepower. Unlike typical car/truck horsepower number gamesmanship - since the PTO rpm is usually standard at 540 - using either torque or horsepower PTO numbers is equally valid as the rpms for all tractors would be the same.

Example 40 PTO hp is 40 PTO hp is 40 PTO hp (and 389 lb-ft of torque). Doesn't matter whether the prime mover is diesel, gas, propane or steam - a 2 liter or 5 liter engine, or what rpm the engine is turning to get the PTO to 540 rpm. The crankshaft numbers may be drastically different - but by the time you get to the PTO output - those differences have basically been roughly cancelled out by the intervening gear train.

The next most important number is the torque rise - how well the engine will resist bogging down - and that will vary significantly due to motor size/type - but that's a much tougher number to pry out of the manufacturers.

And you're right - the peak crankshaft torque of the little CUT diesels is often 3 times the gross engine hp number, give or take a bit.

 

[Steve_in_Ont]

Actually, HP just equals Torque * RPM / 5252. (English units only). So HP is really just the ability to produce torque at speed (RPM).

Torque rise is also an interesting number... It's just the percentage growth from the torque produced at the rated (generally close to high idle) RPM, to the peak amount produced somewhere lower in the RPM range (generally refered to as "peak torque RPM"). So there are two ways to increase your "torque rise" figure - Have a high peak torque (this is the way that most people see this figure), or produce a low torque amount at rated (this is more common than most realize, and is essentially how Mack rates their engines, which have a reputation for high torque rise).

 

[thcri]

Steve,

Does Mack still make the Maxidyne engine. I use to drive an 18 wheeler that had that engine over 25 years ago. If I remember you ran the motor from 1100 to 2200 RPM's. That was the range with a 5 speed transmission. That thing would get up an go pretty good and handle the hills just as good as a 13 or 18 speed tranny.

murph

 

[Steve_in_Ont]

Murph - Mack currently sells an engines that they call an E7. However, every year their E7 looks more and more like a Volvo VED12 (Volvo owns Mack). My guess is that by 2007 (the next significant reduction for on-highway emissions regulations) the Mack will be just a re-branded Volvo engine. If Volvo is smart they will do this very quietly so as not to erode the brand value of Mack.

 

[thcri]

Yes now that you say that I knew Mack was owned by Volvo. I wonder how many big companies are owned by Foreign. I think it is more than not.

murph

 

[BB_TX]

I think the answer is very basic. Everyone is familiar with the term horsepower. Very few are familiar with torque as far as understanding how a torque rating relates to tractor size or power. If you told someone your tractor had 300 ft lbs torque, they would probably just stare at you with a blank look on their face. /forums/images/graemlins/crazy.gif

 

[cowboydoc]

And it's also why people don't understand why a 40 hp from the old days would pull a baler, haywagon, plow, disc, planter, etc. but it's not someting to attempt with a CUT even though the hp ratings are the same.

 

[Anonymous Poster]

If I am understanding this correctly,you guys are saying a 30 hp tractor is normally somewhere in the neighborhood of 200-300 lb/ft of torque? /forums/images/graemlins/shocked.gif HOLY $%*T!! I am amazed.I knew they had to make way more torque than hp but this is mind numbing. I mean, I know diesels are torque monsters,but we're talking 100 cid motors on average. For comparison the 454cid motor in my truck makes roughly 250hp & 400 ft/lb's of torque. This gives me a new perspective on these units. The only tractor I've ever been on in my life was an old late 70's ford something thousand series 2wd. All I did with it was plow,disc & bush hog. It was my grandfather's "garden" tractor ( what he called a garden,myself & I'm sure alot of us other city boys called a farm, 4-5 acres planted ).