Whats the difference and how do they relate?

 

If this is to simple or vaque I apologize.
HP = Torque * RPM * Conversion Factor
(HP is unit including time keep that in mind)

Torque is a force that imparts Twist or rotation.
RPM revolutions per minute.
If torque stays constant and rpm increases HP increases.
If torque increases and rpm stays constant HP increases.
etc..
If you are comparing power tools,DC motor instance -
Increasing current - increases torque
Increasing voltage - increases rpm

check out
http://www.fordmuscle.com/archives/2001/05/horsepower/
check out a motors torque curves -Torque vs RPM-

Hope this helped a little,

 

Buddy is right, But an easier way to put it is...

say:

300HP@5000RPM <----------Horsepower
350lbs.ft@3400RPM <----------Torque

When you rev an engine to 3400 your only getting a little bit of horsepower say 200 now the twisting force on the flywheel is 350FTlbs and thats it, then the RPM continues til it hits 5000, this is when you get the most power, no more power can be made from the engine, so its pointless to go past 5000RPM, this is when you blow bearings and ##### like that, not a good idea. See with an automatic transmision say with a torque converter stall of 2500, If it is totally loaded right down, the engine will rev to 2500 and stay there till it gets moving, The engine is probably only producing 250lbfts of torque and about 150 HP. this is enough to get it going.... Say a standard transmission, you can rev the engine till it hits 3400RPM then release the clutch this will get you going faster becasuse the more turning power of the crankshaft= go go. HP is the force acting on the turning of crank and torque is the twisting force... Make sense good

 

Nutshell anwser,
Torque is how fast you can go, horsepower is how fast you get there.

 

A better "simple" explanation is:

Horsepower is how FAST work is done, and torque is how MUCH work is done. A school bus is slow when it's empty and full right? There isn't that much difference in acceleration, because it has a diesel engine with low hp (low RPM) and high torque.

Arctic cat's 1000cc 3 cyl 2 stroke snowmobile engine makes 172hp and 97 ft-lbs of torque. 172hp is more than a 300ci 6 cyl truck engine (160hp EFI). Could this 3 cyl 1000cc engine push a truck? Not very well, but in a snowmobile it SCREAMS (largest engine ever put in a snowmobile). High horsepower-low torque. Now this snowmobile engine can spin as high as 8500 RPM, and the bus' diesel about 3000 RPM, Hence a lower HP figure.

Really, torque is the amount of twisting force (you measure torque on a torque wrench in inch or foot lbs). Horsepower is a mathematical equation of torque and RPM. I can time myself running up stairs, measure the distance, put it into a formula and come out with around 1.2hp generated by me (physics class).



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Also there is an RPM where torque and horsepower will ALWAYS be the same numerical value. I think its 5230rpm. It has to do with the mathematical formula used to calculate HP from TQ. Check out any perfromance mag. If they list the graphic curves from a dyno run the 2 curves will cross at 5230. The torque curve is dropping off as the HP curve is coming up.

 

Good answers guys!

HP = ( Torque x RPM ) / 5252

-Torque in Pound-feet

This makes the Torque and Horsepower curves cross at 5252 RPM's

Torque measures how much force an engine can generate, Power is the rate-based measurement of how fast that force is producing work. To produce work an engine must move something, not just simply exert a static force.

Force is just standing there looking at that bathroom scale under your feet

Work is running up and down those hills or stairs (moving that lard) in order to do something about it

 

250hp + 69' XL = fast (3800 lbs)
210hp + 00' Eclipse = faster (3200 lbs)
120hp + 00' ZRX100 = fastest (485 lbs)

All off the above =

 

That actual physicist explanation, for those interested:

Torque is Force * distance away from the center of rotation. It is used to determine force from an object moving in a circular path.

Horsepower is work. Work is force time the distance over which the force is applied. For instance, lets say I have two identical rockets, but I launch one while moving at 50 mph and the other from a standstill. They would both produce the same amount of force from their same-sized engine, but the 50 mph rocket will do more work because it is applying that force over more distance (more later). Conversely if we stick both rockets in a vat of JB Weld and light them, neither has done any work because neither has moved--no matter how long they burned.

So how does this relate to engines? Well, the torque an engine can produce is a measure of the amount of rotational force it can apply if you attache a foot long stick to the output shaft. Horsepower (or work) would then be how long that engine applies that much force over a given distance. The common misconception is to gauge this on how long you have the accelerator to the floor, but it actually doesn't work that way.

Remember the rockets? If we had one burn for 30 sec and one for 60 sec, they wouldn't produce the same force because they would still have the same fuel load. Thus the 60 sec rocket _must_ run at half fuel use and would produce half the amount of force (at any given instant). If it traveled twice the distance it would be the same work with half the force, farther and it's more work, etc. In auto's there is an equivelent item that lets you burn that same amount of fuel to produce that thrust over a greater distance. It's called final gear ratio. It should make sense if you think about it...it's the actualy number of reveloutions the wheels made for a given amount of force, or fuel burn (and efficency of converting that burn to rotational force). The top of the torque curve is the RPM at which the amount of fuel burned is producing the most force (pure chemistry of the combustion producing the most free energy). The curve drops off because of not enough oxygen, backpressure, etc. If you had a perfect engine it would keep making more torque as the RPM's went higher, without limit.

So the big question now is... how the hell can your torque curve drop while your horsepower curve keeps going up? Well remember that horsepower is force times distance. If the amount your torque drops is more than made up by the extra revolutions the engine is making, that extra distance your travelling will make it up. This is why a flat torque curve is nice in racing. This is also why big truck have big torque and crappy horsepower.... they are geared low and produce highest torque at low RPMs, so to have a really high HP rating, they'd need 20+ gears (which weighs a lot, which requires a bigger engine to carry around or even more gears to keep on the max torque, ... see the cycle?)

I hope that helps some. If I made a mistake, please correct me

 

 

[updated:LAST EDITED ON 12-Nov-02 AT 12:03&nbsp;PM (EST)]After some followup research and discussion, I have a small mistake. Horsepower is actually power (seems intuitive, doesn't it). The difference between power and work is pretty simple

Power is just the work you do divided by time. If you do the same amount of work in a shorter amount of time, the power is greater.

Lets go back to the similar rocket ships. Instead of seeing how far they go on a burst of fuel, lets set a distance from where they start at which point we can measure the time to get there. Let's say one rocket gets there first (say, less air friction or tailwind). The Force exerted by the engines is the same because the rockets are the same. The distance traveled is _also_ the same, because we stopped measuring at the line; thus work is the same. However, since they arrived at different times, the power is not the same.

In auto engines, we have to have a set time over which to measure engine performance. Otherwise I could say my 4-banger can do huge amounts of work by gearing it really high and giving it a LOT of time & distance to cover to get up to speed and stay there. Thus, we use power rather than speed.

Sorry for this error