I have been asked recently what is Torque. In short, Torque is the static measurement of force. After giving that answer, I was asked how does that apply to an engine. While the answer is the same, the understanding can be a little bit....hummm, difficult to wrap your head around.
Below is an old Car Craft article that I dug up and thought others may like to read in order to have a better understanding of what torque is and how it works. It also explains why hp & tq cross values at 5252 rpm on a dyno sheet.
Hope everyone enjoys.
Engines don't make horsepower; they convert fuel into torque. Torque is the twisting force imparted to the crank flange and then transmitted to the transmission and the rest of the drivetrain. To some degree torque is the grunt that gets things moving, and horsepower is the force that keeps things moving. An engine is most efficient at its torque peak, wherever that happens to occur. Below the torque peak, engines generally have more than enough time to fill the cylinders; above the torque peak, they don’t have enough time to completely fill the cylinders. This is generally beneficial in that it lets engines produce most of the desirable grunt work (torque) at lower engine speeds, which means reduced wear-and-tear and better fuel economy. The ability to extend an engine’s speed-range allows it to stretch that torque curve out farther, provided that the high-speed efficiency is there to make horsepower.
Power is torque multiplied by engine speed to produce a measurement of the engine's ability to do work over a given period of time. The story of its origin is well known, but worth repeating, briefly. In the 18th century, steam engine inventor James Watt sought a way to equate the work his steam engine could perform to the number of horses required to perform the same task. Watt performed simple tests with a horse as it operated a gear-driven mine pump by pulling a lever connected to the pump. He determined that the horse was capable of traveling 181 feet per minute with 180 pounds of pulling force. This multiplied out to 32,580 lbs-ft per minute, which Watt rounded off to 33,000 lbs-ft per minute. Divided by 60 seconds, this yields 550 lbs-ft per second, which became the standard for 1 horsepower. Thus, horsepower is a measure of force in pounds against a distance in feet for a time period of one minute. By substituting an arbitrary lever length for the crankshaft stroke, you can calculate the distance traveled around the crank axis in one minute multiplied by engine speed (rpm) and known torque to arrive at the formula for horsepower:
Because torque and rpm are divided by 5252, torque and horsepower are always equal at 5252 rpm. If you solve the equation at 5252 rpm, the rpm value cancels out, leaving horsepower equal to torque. If you plot torque and horsepower curves on a graph, the lines will always cross at 5250 rpm (rounded off). If they don't, the curve is undoubtedly bogus.
Torque is the static measurement of how much work an engine does, while power is a measure of how fast the work is being done. Since horsepower is calculated from torque, what we are all seeking is the greatest-possible torque value over the broadest-possible rpm range. Horsepower will follow suit, and it will fall in the engine speed range dictated by the many factors that affect the torque curve.
Increased displacement is the easiest way to achieve increased torque. Very large cylinders and a long stroke offer the greatest cylinder volume and overall piston area for the fuel charge to push against the crankshaft or lever, if you will. Stationary industrial engines that produce tremendous amounts of torque are typically quite large. The mass and bulk of one of these engines makes extremely large displacement engines impractical for use in cars.
Hence, we are limited to displacement values that are easily packaged within the confines of your typical automobile engine compartment. The practical limit is between 400-500 cubic inches for most large automobile engines. Big-block engines in this range deliver tremendous torque, and they are easier on parts for the same amount of power output. Car crafters have stretched displacement out as far as 800 cubic inches with highly modified cylinder blocks and crankshaft strokes, but these engines are not practical or economical for general high-performance applications.
This leaves us searching for ways to increase torque in smaller engines by increasing efficiency through the manipulation of mechanical components, gas dynamics and thermodynamics (to increase and harness cylinder pressure). There are many ways to do this, but most involve some sort of tradeoff somewhere in the power curve. To a great degree, we are forced to build engines for greater efficiency within a chosen engine speed range. Some combinations will function very well at low speeds, others will be strong in the mid-range, and still others will only run hard at a high rpm. The key is selecting the combination of components that will stretch and fatten the torque curve (improve efficiency) as much as possible in the driving range we prefer. Our saving grace is the relatively forgiving nature of internal combustion engines wherein torque dissipates gradually as engine speed increases. As long as the induction system can carry the airflow demand created by the cylinders at high engine speeds, the torque curve will remain broad. This allows engine speed and horsepower to carry the engine farther in the rpm range before the net effect of induction restrictions at high engine speeds chokes off efficiency.
That is the end of the article. Below are a few things to note and a little more detail.
Some people get confused when trying to relate Engine Torque and the Torque applied to a bolt when using a wrench. This in turn needs to be elaborated so that it doesn't confuse anyone.
Torque is the the measurement of static force.
As it relates to a bolt. Torque is the amount of force needed to begin moving or rotating the bolt. As soon as that bolt begins to turn and loosen up. The amount of torque required to put the bolt in motion again...will be less but torque is still the measurement of force in a static state. Once the bolt begines to move the applied force (torque) will go down. Its equal to you as a human reaching a peak torque curve just like an engine will. The moment that the bolt breaks loose You have reached the peak torque curve. After it has been broke loose. You as the human, will be on the back side of the torque curve and can no longer apply the same amount of force to the bolt. Just like an engine generating torque hits the peak torque...after that it is not as efficient and can no longer produce an increase of force. So, the torque curve goes done. When the bolt breaks loose, because we (the human) can no longer apply more force then the resistance of the bolt will allow from a static state. We are unable to produce the same amount of torque to a loose bolt as we did to a tight bolt.
Same thing in reverse using a torque wrench to tighten a bolt. Its the amount of force it takes to move the bolt. But, the force is still dependent on the amount of resistance. If you tighten a bolt up to a reading of 120 ft lbs of torque. That bolt will remain static until you hit 120+ ft lb of torque and get the bolt to rotate. When you are trying to turn a bolt with only 60 ft lb's of torque and the bolt has allready been torqured to 120 ft lb. The bolt is not going to move. It is going to remain static while you still have 60 ft lb of torque applied. In the static state. Torque does not go up or down. Its just simply applied. So, again...even in this case and I think it can be seen a little clearly with this example. the applied force (torque) is static and has a dynamic amount of 60 ft lb of torque being applied in a static state.
With an engine, its a little different. The principle is the same but we are no longer looking at how the principle is applied to something that is in a static state and measure what it effectively takes to move it. And watching the value of applied force decrease as soon as it begins to rotate. Rather, we are applying the principle to measure what the applied force something is capable of generating, that begins in a static state and watch the value of force increase even after the object itself, is connected to something that is no longer static and has begin to move. Even at that point...you have to remember that torque is still the measurement of static force. This is why some people get a little lost when you say that torque is the measurement of static force.
You also have to note: Torque readings on an engine is a measurement to the regard of.....what amount of force it is capable of producing. Not the amount of force required to turn it or whats required to turn the components connected to it. In order to relate numbers that are given for torque on an engine to a torque wrench and a bolt or nut. You would have to relate that to someone welding a nut to a table. Taking an "I-Beam" torque wrench with a max reading of 1000 ft lbs. Putting the torque wrench on the welded down nut and pushing it as hard as you can. Then record your highest reading. Again, Nothing is moving but you are measuring what your max capability of producing torque is.
The amount of torque lost from the flywheel to the rear wheels is the answer for what amount of force it takes to move through the drivetrain. That would be the measurement of force or energy absorbed before completing its journey to the rear wheels. The left over force is what you will be applying to the resistance of the tires to the pavement. This is where torque measurements and how that equals greater performance comes together....its where the "rubber meets the road" per say...lol
Because an engine is already moving (no longer static) and the torque value generally starts low and begins to increase to a certain point and then decreases. It's all the same thing. The exception being that a human is not capable of producing more energy then resistance will allow. With the internal combustion engine. The more fuel, spark, and air that you can feed it and generate a bigger explosion to create energy. The more efficiently it can generate energy. Thous more energy can be generated then what the resistance will allow.
Below is an old Car Craft article that I dug up and thought others may like to read in order to have a better understanding of what torque is and how it works. It also explains why hp & tq cross values at 5252 rpm on a dyno sheet.
Hope everyone enjoys.
Engines don't make horsepower; they convert fuel into torque. Torque is the twisting force imparted to the crank flange and then transmitted to the transmission and the rest of the drivetrain. To some degree torque is the grunt that gets things moving, and horsepower is the force that keeps things moving. An engine is most efficient at its torque peak, wherever that happens to occur. Below the torque peak, engines generally have more than enough time to fill the cylinders; above the torque peak, they don’t have enough time to completely fill the cylinders. This is generally beneficial in that it lets engines produce most of the desirable grunt work (torque) at lower engine speeds, which means reduced wear-and-tear and better fuel economy. The ability to extend an engine’s speed-range allows it to stretch that torque curve out farther, provided that the high-speed efficiency is there to make horsepower.
Power is torque multiplied by engine speed to produce a measurement of the engine's ability to do work over a given period of time. The story of its origin is well known, but worth repeating, briefly. In the 18th century, steam engine inventor James Watt sought a way to equate the work his steam engine could perform to the number of horses required to perform the same task. Watt performed simple tests with a horse as it operated a gear-driven mine pump by pulling a lever connected to the pump. He determined that the horse was capable of traveling 181 feet per minute with 180 pounds of pulling force. This multiplied out to 32,580 lbs-ft per minute, which Watt rounded off to 33,000 lbs-ft per minute. Divided by 60 seconds, this yields 550 lbs-ft per second, which became the standard for 1 horsepower. Thus, horsepower is a measure of force in pounds against a distance in feet for a time period of one minute. By substituting an arbitrary lever length for the crankshaft stroke, you can calculate the distance traveled around the crank axis in one minute multiplied by engine speed (rpm) and known torque to arrive at the formula for horsepower:
Because torque and rpm are divided by 5252, torque and horsepower are always equal at 5252 rpm. If you solve the equation at 5252 rpm, the rpm value cancels out, leaving horsepower equal to torque. If you plot torque and horsepower curves on a graph, the lines will always cross at 5250 rpm (rounded off). If they don't, the curve is undoubtedly bogus.
Torque is the static measurement of how much work an engine does, while power is a measure of how fast the work is being done. Since horsepower is calculated from torque, what we are all seeking is the greatest-possible torque value over the broadest-possible rpm range. Horsepower will follow suit, and it will fall in the engine speed range dictated by the many factors that affect the torque curve.
Increased displacement is the easiest way to achieve increased torque. Very large cylinders and a long stroke offer the greatest cylinder volume and overall piston area for the fuel charge to push against the crankshaft or lever, if you will. Stationary industrial engines that produce tremendous amounts of torque are typically quite large. The mass and bulk of one of these engines makes extremely large displacement engines impractical for use in cars.
Hence, we are limited to displacement values that are easily packaged within the confines of your typical automobile engine compartment. The practical limit is between 400-500 cubic inches for most large automobile engines. Big-block engines in this range deliver tremendous torque, and they are easier on parts for the same amount of power output. Car crafters have stretched displacement out as far as 800 cubic inches with highly modified cylinder blocks and crankshaft strokes, but these engines are not practical or economical for general high-performance applications.
This leaves us searching for ways to increase torque in smaller engines by increasing efficiency through the manipulation of mechanical components, gas dynamics and thermodynamics (to increase and harness cylinder pressure). There are many ways to do this, but most involve some sort of tradeoff somewhere in the power curve. To a great degree, we are forced to build engines for greater efficiency within a chosen engine speed range. Some combinations will function very well at low speeds, others will be strong in the mid-range, and still others will only run hard at a high rpm. The key is selecting the combination of components that will stretch and fatten the torque curve (improve efficiency) as much as possible in the driving range we prefer. Our saving grace is the relatively forgiving nature of internal combustion engines wherein torque dissipates gradually as engine speed increases. As long as the induction system can carry the airflow demand created by the cylinders at high engine speeds, the torque curve will remain broad. This allows engine speed and horsepower to carry the engine farther in the rpm range before the net effect of induction restrictions at high engine speeds chokes off efficiency.
That is the end of the article. Below are a few things to note and a little more detail.
Some people get confused when trying to relate Engine Torque and the Torque applied to a bolt when using a wrench. This in turn needs to be elaborated so that it doesn't confuse anyone.
Torque is the the measurement of static force.
As it relates to a bolt. Torque is the amount of force needed to begin moving or rotating the bolt. As soon as that bolt begins to turn and loosen up. The amount of torque required to put the bolt in motion again...will be less but torque is still the measurement of force in a static state. Once the bolt begines to move the applied force (torque) will go down. Its equal to you as a human reaching a peak torque curve just like an engine will. The moment that the bolt breaks loose You have reached the peak torque curve. After it has been broke loose. You as the human, will be on the back side of the torque curve and can no longer apply the same amount of force to the bolt. Just like an engine generating torque hits the peak torque...after that it is not as efficient and can no longer produce an increase of force. So, the torque curve goes done. When the bolt breaks loose, because we (the human) can no longer apply more force then the resistance of the bolt will allow from a static state. We are unable to produce the same amount of torque to a loose bolt as we did to a tight bolt.
Same thing in reverse using a torque wrench to tighten a bolt. Its the amount of force it takes to move the bolt. But, the force is still dependent on the amount of resistance. If you tighten a bolt up to a reading of 120 ft lbs of torque. That bolt will remain static until you hit 120+ ft lb of torque and get the bolt to rotate. When you are trying to turn a bolt with only 60 ft lb's of torque and the bolt has allready been torqured to 120 ft lb. The bolt is not going to move. It is going to remain static while you still have 60 ft lb of torque applied. In the static state. Torque does not go up or down. Its just simply applied. So, again...even in this case and I think it can be seen a little clearly with this example. the applied force (torque) is static and has a dynamic amount of 60 ft lb of torque being applied in a static state.
With an engine, its a little different. The principle is the same but we are no longer looking at how the principle is applied to something that is in a static state and measure what it effectively takes to move it. And watching the value of applied force decrease as soon as it begins to rotate. Rather, we are applying the principle to measure what the applied force something is capable of generating, that begins in a static state and watch the value of force increase even after the object itself, is connected to something that is no longer static and has begin to move. Even at that point...you have to remember that torque is still the measurement of static force. This is why some people get a little lost when you say that torque is the measurement of static force.
You also have to note: Torque readings on an engine is a measurement to the regard of.....what amount of force it is capable of producing. Not the amount of force required to turn it or whats required to turn the components connected to it. In order to relate numbers that are given for torque on an engine to a torque wrench and a bolt or nut. You would have to relate that to someone welding a nut to a table. Taking an "I-Beam" torque wrench with a max reading of 1000 ft lbs. Putting the torque wrench on the welded down nut and pushing it as hard as you can. Then record your highest reading. Again, Nothing is moving but you are measuring what your max capability of producing torque is.
The amount of torque lost from the flywheel to the rear wheels is the answer for what amount of force it takes to move through the drivetrain. That would be the measurement of force or energy absorbed before completing its journey to the rear wheels. The left over force is what you will be applying to the resistance of the tires to the pavement. This is where torque measurements and how that equals greater performance comes together....its where the "rubber meets the road" per say...lol
Because an engine is already moving (no longer static) and the torque value generally starts low and begins to increase to a certain point and then decreases. It's all the same thing. The exception being that a human is not capable of producing more energy then resistance will allow. With the internal combustion engine. The more fuel, spark, and air that you can feed it and generate a bigger explosion to create energy. The more efficiently it can generate energy. Thous more energy can be generated then what the resistance will allow.
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