Horsepower vs. torque

[JDgreen227]

When you buy something with an engine that is rated by both horsepower and torque, which rating do you pay more attention to? For me, in an automobile engine that is only subject to passenger use, horsepower is the factor. For my tractor and truck, I based my choices on the torque rating instead. Not sure if others do it that way themselves.

A guy I used to work with asked me one time (he wasn't very mechanical) to explain the difference in the two ratings. I told him:

"Horsepower is what determines how fast you can be traveling before you hit a brick wall, torque determines how far you will travel through it after the impact".

Have I got that right, or not?

 

[Richard]

I was always told "Torque is what GETS you going and HP is what KEEPS you going"

Given the over kill I have at home (full sized industrial backhoe/loader) I don't worry about either one.

Actually, that's not 100% true... although I don't worry about the HP or torque situation, I DO find myself listening while working, to the wonderful whine of the turbo.

Probably strange, but true.

 

[LD1]

HP is derived from torque. It is nothing more than a calculation using the torque because the HP cant directly be measured.

And the best description that feel makes the most sense is:

Torque is how much work CAN be done.

HP is how fast it can get said work done.

So when it comes to things like towing, torque is the measure that defines how much it can tow. HP defines how fast over a given distance it can tow that load.

For a hypotherical example:

Truck 1 has 200HP and 1000ft-lbs of torque. It can tow a pretty heavy trailer, just be a little sluggish.

Truck two has 500HP but only 500ft-lbs of torque. The 500HP looks great on paper, but cant even move the load.

Of course there are other variables as well, like gearing and traction. But that is a whole other issue.

 

[Grand_Pooba]

Horse power = Torque x RPM divided by 63,025. Which means an engine with less torque can generate the same HP as a higher torque motor by running at higher RPM.

 

[Mickey_Fx]

Torque is the rotational force around an axis. It is something that can be physically measured. On the otherhand, HP is a mathematical calculation that defines how much work can be done over a given time period. (not going into the math here)

You can apply torque to an object without it moving. Without movement there is no work being accomplished thus no HP calc is possible.

 

[SandburRanch]

Torque consumes HP.:laughing: If in doubt torque 96 Waukesha head bolts to 600 lbs. in 96 minutes with an ambient temp. of about 120 and you'll find you don't have much HP remaining with your tongue hanging out.:laughing:

 

[Richard]

I don't remember the number, but I remember reading once that the HP/Torque curves always intersect at a certain point (I think certain RPM) because of how the HP is calculated.

 

[LD1]

Horse power = Torque x RPM divided by 63,025. Which means an engine with less torque can generate the same HP as a higher torque motor by running at higher RPM.

you got that wrong. HP= torque x RPM divided by 5252

I don't remember the number, but I remember reading once that the HP/Torque curves always intersect at a certain point (I think certain RPM) because of how the HP is calculated.

You are right. They will ALWAYS cross @ 5252RPM if the engine can rev that fast. Simply because given the equation above, if RPM is 5252 and the constant is 5252, they cancel out. this leaving torque = HP.

Below 5252RPM, torque is ALWAYS higher then HP. And Above that RPM, HP is ALWAYS higher.

That is why if a vehichle has more torque down low in the RPM range, it will also have more HP down their as well.

 

[JDgreen227]

I don't remember the number, but I remember reading once that the HP/Torque curves always intersect at a certain point (I think certain RPM) because of how the HP is calculated.

My GMC (300 hp Vortec 6000 V8) horsepower and torque curves intersect at close to 2600 rpm, the 4800 and 5300 V8's (these are all Y2K figures) at very close to the same point...so you must be onto something there. :thumbsup:

 

[LD1]

My GMC (300 hp Vortec 6000 V8) horsepower and torque curves intersect at close to 2600 rpm, the 4800 and 5300 V8's (these are all Y2K figures) at very close to the same point...so you must be onto something there. :thumbsup:

That is IMPOSSIBLE. Plain and simple. The math just doesnt support those figures