What is the link between torque and rpm?

Joe98

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A review of a Wrangler states that the Wrangler can achieve 260 lb foot of torque at 4,800 rpm.

What is the link between torque and rpm?
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vavaroutsos

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A review of a Wrangler states that the Wrangler can achieve 260 lb foot of torque at 4,800 rpm.

What is the link between torque and rpm?
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It is a curve that usually looks like a mountain, torque increases to some mid RPM, then starts to fall off at high RPM. But engines can be tuned for different shaped curves. The 3.6L has a fairly flat torque curve, and I have seen some after market tunes than make it really flat. Torque x RPM x units constant = HP.
 
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Joe98

Joe98

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When you say the "torque curve", are you referring to a graph: rpm vs torque?

As I push the accelerator, the rpm's increase and the torque increases, helping me over a rock. If the rpm's actually reached 4,800 and I have not moved, that implies when I do move, I might fly over that rock and damage the vehicle.

What do people think?
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hutchman

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There is no direct link between torque and engine speed/rpm. As stated, 260 lb-ft at 4,800 rpm means that there is 260 lb-ft of torque applied to the crank @ 4800 rpm in this particular engine. This torque produced is directly proportional to volumetric efficiency.....not engine rpm.

There is a link however between power and engine rpm. The mathematical equation for horse power is:

HP = Torque x rpm/5252

From this you can see that HP is proportional to both engine speed and Torque.

When Torque goes up at a given rpm, HP goes up.

When engine speed/rpm goes up at a given torque, power goes up.

Torque is a force. Apply that force to a mass with no movement and you have accomplished no work. Apply the force to a mass and move the mass, you have work. If you measure the work performed over a tme period, you have power.

So the question always comes up, "Which do you want your engine to make, torque or horse power?" And the answer is the the two terms are not mutually exclusive. Since we are concerned with the rate of doing work.....moving our Jeep more quickly, we want more power.

From the above equation, we see that to increase power at a given RPM, we want to increase torque. At a low engine speed then, we need more torque to climb a hill more quickly. This is done by engine design or I suppose throttle position also.

The other way to increase power is to increase engine speed. Higher engine speed results in more power and can be accomplished by the driver with throttle position or changing gears in the transmission or both.

The thing to remember is that power is the measure of the rate of doing work. If you want to go up a hill quicker, it takes more power. Power increase at a given rpm comes from an increase in torque. Power is also increased by increasing engine rpm.
 

Badweissenbier

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Or- torque pulls the trailer, horsepower wins the race
 

RedTRex

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Not to complicate the answer but changing gear ratios also multiplies the torque....which is why in 4LO you can crawl and climb quite well
 

Rockreid

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Just to add, Electric motors typically have most of their torque from 0 rpm. Thermal realities are why available power starts to drop off at higher speeds. This website gives a short rundown of how a Tesla can achieve their mindbending drag strip numbers and provide a goosebump tingling excitement how how a upcoming plug-in Wrangler can climb at crawl speeds.

https://www.quora.com/How-are-Tesla...h-power-compared-to-the-gasoline-counterparts
 

WXman

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Torque is how much power an engine can make. Horsepower is how fast it can do it.

That's why a diesel can pull more weight, but does so slowly.

The 3.6L engine doesn't make much power, but the power it does make comes on quickly (high horsepower) and the powerband is nice and flat.
 

vavaroutsos

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Torque is how much power an engine can make. Horsepower is how fast it can do it.

That's why a diesel can pull more weight, but does so slowly.

The 3.6L engine doesn't make much power, but the power it does make comes on quickly (high horsepower) and the powerband is nice and flat.
Torque is not power, it is a measure of rotational force. You can have lots of torque with no power. Power is a measure of the rate at which work (force through distance) is done.

A deisel pulls hard because it creates a lot of torque at low RPM. It may not produce much HP since it won't rev very high.
 

WXman

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Torque is not power, it is a measure of rotational force. You can have lots of torque with no power. Power is a measure of the rate at which work (force through distance) is done.

A deisel pulls hard because it creates a lot of torque at low RPM. It may not produce much HP since it won't rev very high.
Rotational force is power.

Torque is a measurement of that power.

Horsepower and torque are related through mathematical formulas, and horsepower being generally the speed at which a certain amount of work can be completed. If you go to a dyno shop, they measure torque, not horsepower. They derive horsepower from the power (torque) the engine made and a few other variables.

My illustration was simply an attempt to put it into laymen terms for ease of understanding the relationship between the two.
 

digitalbliss

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The definition of power is
power = work/time

You have to be VERY careful with your terms with this topic
 

Raylan Givens

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As I push the accelerator, the rpm's increase and the torque increases, helping me over a rock. If the rpm's actually reached 4,800 and I have not moved, that implies when I do move, I might fly over that rock and damage the vehicle.

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The engine explodes at 4,801 RPM
 

cbrenthus

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some simple explanations, if you want more complicated, some users have already posted that.

1. Torque is acceleration, horsepower is top speed
2. Torque is how many shingles you can carry up a ladder to the roof at once. Horsepower is how many you shingles you can carry up to the roof in a specified amount of time, regardless of number of trips.

So, using the #2 example, we can see how some engines have high torque with less horsepower, or lower torque with higher horsepower. Let's say you have a big dude that can carry 20 shingles at a time, but he get's winded easily and can only make 1 trip every 10 minutes. This guy carries 120 shingles in an hour. Then you have another guy that can only carry 10 shingles at a time, but can make a trip every 5 minutes. He also carries 120 shingles in an hour. so therefore, you have guy 1 with torque of 20 and hp of 120, and guy 2 with torque of 5 but equal hp at 120.

Now let's say you have a guy that can carry 50 at a time, but only twice an hour - 50tq/100hp
100 at a time but only once every 2 hours - 100tq / 50hp
10 at a time but a trip every 2.5 minutes - 10tq / 240hp

Keep in mind, with an engine, that hour I used as an example is the RPM band up to the limit.
 
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