whats the real difference between torque and hp? please make it easy to understand. tIA

 

Torque is just how much your motor can pull(I cant think of a way to explain it) and horsepower is torque times RPM.

*edit*
I would tell you to look it up on howstuffworks.com but that's like an eight page explanation of something simple.


[Modified by lazy bum shaughn, 11:16 AM 4/5/2003]

 

i still dont understand...but thanks anyways. anyone else wanna try?

 

think of it this way, if u tied ur car to a tree, the torque is whats gonna pull that tree down. u know those big *** trucks, dodge ram, ford f550, big *** semis, they have torque. torque is what gets u moving. semis have like 300 horsepower and like 1000lbs of torque

 

To me, horsepower is an equivalent of torque with time factored into the mathematical definition.

It could take you all day to produce 100lb*ft of torque by moving a breaker bar 2 ft with 50 lb's of force and it would still be 100lb*ft of torque, but the amount of horsepower you've created is very minimal (analogous to running an engine at low rpm w/ an assumed flat torque curve).

Not a very good transition in streamlined logic, but....
When I look at dyno plots, I have a tendency to look at the torque curve characteristics more than the horsepower curve. The torque curve is easier to analyze to see where it likes to make that power and how the engine is breathing at particular rpm intervals. An engine makes more power where it breathes better.

When you see engines that have higher peak torque values than peak horsepower, it's indicative of an engine that likes to breathe well at lower rpm's and not so well at higher rpm's (eg: diesel engines). When you look at the torque curve, it'll quickly develop its peak torque with nice midrange, but the torque curve will quickly fall off due to breathing inefficiency at higher rpm's.

Honda VTEC engines produce power a little differently than in the above example in that the torque is usually very flat over a wide range of rpm's (God bless VTEC) and the horsepower rises linearly as a function of rpm (not so much as a function of torque b/c the curve is basically flat).

Honda's don't lack torque simply b/c they're Honda's or that they're inefficient, it's more of a function of small engine size. VTEC heads and the cams matched to the heads breathe exceptionally well over a wide range of rpm's and the torque curve shows it.

Blehf. Thinking too much addles the brain.

 

Think of it this way...

Torque is how hard the engine's pulling on the car. HP is this same force, multiplied by how fast the car is going. Torque is what pulls the car, but it only counts when it can be applied at some given speed. So HP is just as important as torque, because it incorporates the speed (rpm). Say you built an engine that had 1000 lbf-ft of torque, but it redlines at 50 rpm. That's only 9.5 hp. Good for pulling stumps out of the ground, but not very fast.

Imagine you tied a rope to the front bumper, & your buddy sat in the car with his foot on the brakes. You could pull on the rope with, say, 100 lb of force, but there's no power because the car's not actually moving (speed = zero).

Now say your buddy releases the brakes & lets you pull the car. You pull with the same 100 lb of force, but the power is small because you aren't moving very fast.

Actually, once the car gets moving, you can't keep pulling with the same force if you can't run fast enough to keep up. That's like your engine's torque dropping off (running out of breath) near its redline.

Now say you turn down a big hill. You can't even run fast enough to avoid getting run down. That's like mis-shifting into 2nd & blowing a rod.

 

Torque is a measure of how much a force acting on an object causes that object to rotate. The 'acting' (pushing, turning) is done and measured at set distance from the axis things are spinning around.

We most often use pounds for the measure of force, and a foot for distance... which is where 'foot pounds' comes from when speaking of torque.

Torque has no 'time' dimension -- time is not taken into account -- it is a measure of what is happening at 'the moment'. So torque can tell you how hard something is being turned (force), but not how much work is/was done or how fast it is turning with that force.

To measure WORK you are measureing FORCE and TIME.

Horsepower takes torque, and adds a 'time' factor, and therefore tells you about how much work was done (energy expended).

For example, it may take 10 ft/lbs of force to turn the handle and raise a bucket of water from down in the well. That number does not tell you how long you had to turn it.. was it 100' down, or 200'? How do you measure that? RPM (how fast it turns (revolutions) in a period of time (minute)), and force (ft/lbs). HP is the measure that works for you, and HP will have a direct relationship with how tired your arm is when you are done!

Spin it slowly and take longer, or spin it fast and take less, the same amount of work will happen, right? (hint -- right).

Horsepower is also an *ARBITRARY* amount of force measured in a fixed amount of time. What do I mean by arbitrary?

I quote from this link:

"The story goes that Watt was working with ponies lifting coal at a coal mine, and he wanted a way to talk about the power available from one of these animals. He found that, on average, a mine pony could do 22,000 foot-pounds of work in a minute. He then increased that number by 50 percent and pegged the measurement of horsepower at 33,000 foot-pounds of work in one minute. It is that arbitrary unit of measure that has made its way down through the centuries and now appears on your car, your lawn mower, your chain saw and even in some cases your vacuum cleaner!"

Aren't you glad he didn't use a dog to measure the work done?!! "Hey dude, my car has 1000 dog power!" Doesn't work for me...

So, there is a relationship between horsepower and torque. In engines, since they spin to deliver the force, the relationship includes RPM. The same force spinning faster performs more work (++ horsepower).

Here is a formula to calculate horsepower, if you know the torque and RPM:

(Foot-pounds x rpm)/5250 = Horsepower

(horsepower x 5250)/rpm = foot-pounds

More information may be found here:


Here is a fairly easy read:

http://www.fordcobraengines.com/Horsepowerdefine.htm


Enjoy.

Mark

 

Let me try. Torque helps you out on acceleration. The more torque, the quicker you pull out of the hole. Horsepower helps on top end. The more hp, the better and quicker top end.

 

Let me try. Torque helps you out on acceleration. The more torque, the quicker you pull out of the hole. Horsepower helps on top end. The more hp, the better and quicker top end.

 

To accelerate a car, you need both force (torque) and speed (rpm). You need 100% torque on start, and less so as the car goes faster. Because of this, horepower is what ultimately accelerates the car, as it includes both speed and force. The only reason torque comes into play when racing is due to the limitations of the transmission. If you had an infinitely variable transmission with an infinite spread of ratios, the torque rating of an engine would be absolutely irrelevant.

With gearing, you can get any torque at the wheels you want...but not at any speed. So, if you had that infinitely variable trasmission, any engine (even you) could theoretically accelerate the car infinitely fast, but only when it's standing still. How fast you could accelerate it drops off rapidly as speed builds.

I don't know if you understood any of this, but it all comes does to this: horsepower lets you accelerate. The only reason you should even look at the torque rating/ curve is due to limitations of the transmission (which can become very important) and for comfort reasons. But know this: horsepower includes both torque and speed, and is therefore the ultimate deciding factor in how fast a car can accelerate. Torque by itself is no good, because given a lever long enough even you could generate enough of it to move the world...but you won't be moving it very fast.

 

http://www.vettenet.org/torquehp.html