Understanding Torque

[olddog]

Torque is the rotational equivalent to Force, in linear motion.

Back in the stone age, Uglug was the biggest and strongest man around. A rich man was paying people to carry stones from the river to the top of a mountain, to build a stone house. Uglug pushed on a huge bolder all day, never budging it, while the smaller men carried smaller rocks up the mountain. At the end of the day, the smaller men were paid according to the rocks they moved. Uglug was furious, when the rich man wouldn't pay him. Uglug argued he was twice as big as anyone else and he had worked hard. The rich man explained that he had not accomplished anything, as the bolder was still in the same spot.

If I push on a huge bolder with all of my might, I might be able to put 200 or maybe even 300 pounds of Force on the bolder. If the bold does not move, I did no work, on the bolder. However if I push with much less force on a smaller rock and move it a long distance, I have done work. Work is Force times Distance.

W = F * D

When you factor in the time it took to move the rock that distance, you can calculate the Power require to do the Work. You can generate more Power by moving a light rock, a long distance, in a short time, verses moving a heavy rock, a short distance, over a long time.

Hp is the rotational equivalent to Work per unit of time, in linear motion.

So Torque, like force, accomplishes no work, if there is no rotation. When you pull on a wrench and the bolt does not turn, you have accomplished nothing. On the other hand, if you apply a Torque and the object rotates, you have done work, and when you factor in the time it took to rotate an angular distance, you can calculate the Power expended. Or in the case of an engine, the power generated.

So folks listen carefully here. You do not have to calculate the torque to the wheels in each gear at every rpm and graph it, to figure out which gear will give more acceleration at a given speed. If you know the Hp at every rpm (if you know the torque at every rpm then you know the Hp it is simple math) and you know what rpm you will run, in each gear, at a given speed, it is simple to calculate the Hp the engine will make, at a given speed, in each gear. Whichever gear allows the engine to make the most Hp, at that speed, is the gear that will accelerate the vehicle at the highest rate.

Maximizing Torque does not yield maximum acceleration! Maximizing Hp yields maximum acceleration! I cannot shout that loud enough. Hp is the measurement of work per unit of time. It is the the measurement that everyone is trying to figure out, but they do not understand it and ignore it!

Peak Hp always happens well past peak torque, at considerably less torque. Get your rpm at peak Torque in 4th gear, floor it and feel the acceleration. Now get your rpm at peak Torque in 4th gear again, only this time shift down to 3rd gear and floor it. Much more acceleration, right? Yep, and you accomplish it with the engine making less Torque, but more Hp. There's your proof. You've done it a thousand times.

Torque is just rotational force. If nothing moves, all the force in the world will do no work. Work moves your car from point "A" to point "B". Power is the distance per unit of time. If you want to get from point "A" to point "B" in less time, increase the Power. Hp is rotational Power. Folks they understood this in the 19th century. That is why they figured out how to calculate Hp in the first place. They wanted to compare the work a horse could do, to the work an engine could do. Here we are in the 21 century with every learning aid and google at you fingertips, and most people still do not get it.

[eschaider]

Originally Posted by olddog

Torque is the rotational equivalent to Force, in linear motion.

You are close to the mark olddog. The actual definition of torque is the cross product of the vector by which the force's application point is offset relative to the fixed suspension point (distance vector) and the force vector, which tends to produce rotational motion.

Originally Posted by olddog

... If I push on a huge bolder with all of my might, I might be able to put 200 or maybe even 300 pounds of Force on the bolder. If the bold does not move, I did no work, on the bolder. However if I push with much less force on a smaller rock and move it a long distance, I have done work. Work is Force times Distance.

W = F * D

You are correct.

A more precise definition of work is, a displacement of the point of application in the direction of the force.

However we were talking about torque and horsepower not work.

BTW the less force example on the smaller rock for a longer distance is essentially the F-1 engine model. If I take a typical 750 HP F-1 engine that operates at 18,000 rpm that engine only makes 218 ft/lbs of torque.

Now that F-1 engine's 750 HP output is really impressive but if you put that into a Cobra and put a 482" FE that only made 650 HP into another Cobra which one do you think would have the better driving experience? The difference is torque.

Originally Posted by olddog

When you factor in the time it took to move the rock that distance, you can calculate the Power require to do the Work.

Complete agreement again.

The text book definition is, power is the rate of doing work, the amount of energy transferred per unit time.

Originally Posted by olddog

You can generate more Power by moving a light rock, a long distance, in a short time, verses moving a heavy rock, a short distance, over a long time.

Not quite as much agreement here, but close. The power is not generated by moving the rock in this instance, rather it is consumed by the action of moving the rock. The distinction being the difference between generation and consumption.

Originally Posted by olddog

Hp is the rotational equivalent to Work per unit of time, in linear motion.

HP as its naming convention suggests is Power. One HP can be expressed in watts as 745.xx watts or 745.xx newton meters/ second or as we more often hear about it, as 33,000 foot pound-force/minute and it is work per unit time.

Originally Posted by olddog

So Torque, like force, accomplishes no work, if there is no rotation. When you pull on a wrench and the bolt does not turn, you have accomplished nothing. On the other hand, if you apply a Torque and the object rotates, you have done work, and when you factor in the time it took to rotate an angular distance, you can calculate the Power expended. Or in the case of an engine, the power generated.

Complete agreement.

Originally Posted by olddog

So folks listen carefully here. You do not have to calculate the torque to the wheels in each gear at every rpm and graph it, to figure out which gear will give more acceleration at a given speed. If you know the Hp at every rpm (if you know the torque at every rpm then you know the Hp it is simple math) and you know what rpm you will run, in each gear, at a given speed, it is simple to calculate the Hp the engine will make, at a given speed, in each gear. Whichever gear allows the engine to make the most Hp, at that speed, is the gear that will accelerate the vehicle at the highest rate.

Somewhat of a simplification but in general correct for n/a engines.

Where the surprise comes in, is the flat torque curve engines whether electric or supercharged. The supercharged engines will have a power curve that looks like a straight line moving upwards at a 30˚ or 45˚angle (pretty potent engine). Because the area under the power curve continues to grow as the engine speed is increased there is no obvious shift point. With these flat torque curve engines you want to shift before destructive engine speed costs you engine internals.

An interesting observation that some drivers, who are used to n/a engines, make after their first driving experience with a supercharged engine is that it never seems to stop pulling. That driver sensation is a direct result of the essentially flat torque curve that produces the essentially straight line power curve angling upward at 30˚ or 45˚.

In the case of the n/a engine (as we have all experienced) you will actually want to shift beyond not just your peak torque but also peak power to get the benefit of the most area under the power curve to accelerate the car. Again this is because you are looking to optimize the area under that power curve (not torque) that you use to apply power to the wheels.

The electric cars like Tesla have no transmission so the concept of shifting gears does not translate well for them.

Originally Posted by olddog

Maximizing Torque does not yield maximum acceleration! Maximizing Hp yields maximum acceleration! I cannot shout that loud enough. Hp is the measurement of work per unit of time. It is the the measurement that everyone is trying to figure out, but they do not understand it and ignore it!

Actually what you are looking for again is the area under the power curve not just maximum power. The maximum acceleration will be provided by choosing shift points and gear ratios that bracket the horsepower curve capturing the greatest area under the curve, gear change to gear change.

With a n/a engine the torque curve will be concave downwards. Eventually the power curve will also nose over and decline. The optimum shift point is the point at which the area under that power curve in each gear is maximized.

With a supercharged engine the torque curve will be essentially flat with an ever so slightly downwards concave curve. Production supercharged engines, like my BMW for instance, have a very pronounced termination of their flat torque curve — I suspect for warranty expense reasons. Performance supercharged engines, like the one I built for my Cobra, simply go until they break or you get scared.

The flat torque curve of the performance supercharged engine makes selecting shift points a no brainer compared to their n/a brethren.

The torque side of the story is down two more answers.

Originally Posted by olddog

Peak Hp always happens well past peak torque, at considerably less torque.

This is predominately true for n/a engines not so for performance supercharged engines.

Originally Posted by olddog

Get your rpm at peak Torque in 4th gear, floor it and feel the acceleration. Now get your rpm at peak Torque in 4th gear again, only this time shift down to 3rd gear and floor it. Much more acceleration, right? Yep, and you accomplish it with the engine making less Torque, but more Hp. There's your proof. You've done it a thousand times.

This one can be deceiving. In fact you do accelerate harder in third gear than you do in fourth but what you are forgetting is that you are using the mechanical advantage of the transmission's third gear to multiply the torque going to the rear tires. The transmission basically augments the reduced torque the engine has at higher engine speeds while allowing you to realize the benefits of the increased power available at higher engine speeds.

Lets assume we have tires that can hook up in this next example. Lets also assume our engine peaks its power at 6500 rpm. If I stage the car and leave in fourth gear the car will launch but not particularly impressively.

If I do the exact same launch but start in first gear the car will feel like a land based missile. The difference is the mechanical advantage that first gear provided increasing the torque the rear tire saw at launch.

This phenomena is exactly what plagued the Subaru WRX when it was used as a daily driver rather than a race car. Similar story, although not as pronounced for the Honda S2000 cars.

In Cobra replicas the original argument between big block and small block engines (before small blocks got big displacement) was founded in the difference of not just low speed torque but torque everywhere in the engine rpm range. Even in the big block corner the reason for the stroker cranks is the increased displacement and increased everywhere torque that makes the cars so attractive to the driver. Increased torque everywhere will always provide increased power everywhere

Originally Posted by olddog

Torque is just rotational force. If nothing moves, all the force in the world will do no work. Work moves your car from point "A" to point "B". Power is the distance per unit of time. If you want to get from point "A" to point "B" in less time, increase the Power. Hp is rotational Power. Folks they understood this in the 19th century. That is why they figured out how to calculate Hp in the first place. They wanted to compare the work a horse could do, to the work an engine could do. Here we are in the 21 century with every learning aid and google at you fingertips, and most people still do not get it.

There is absolutely no question about more power bringing more thrills but the impact of torque should never be forgotten or misunderstood. Again, just stage your car in fourth gear at the next stop light Grand Prix. The effect will not be as impressive as if you use first gear and its torque multiplication — no matter how close to your peak horsepower rpm you launch at in fourth gear.


Ed

[mikeinatlanta]

Originally Posted by olddog

Torque is the rotational equivalent to Force, in linear motion.

Back in the stone age, Uglug was the biggest and strongest man around. A rich man was paying people to carry stones from the river to the top of a mountain, to build a stone house. Uglug pushed on a huge bolder all day, never budging it, while the smaller men carried smaller rocks up the mountain. At the end of the day, the smaller men were paid according to the rocks they moved. Uglug was furious, when the rich man wouldn't pay him. Uglug argued he was twice as big as anyone else and he had worked hard. The rich man explained that he had not accomplished anything, as the bolder was still in the same spot.

If I push on a huge bolder with all of my might, I might be able to put 200 or maybe even 300 pounds of Force on the bolder. If the bold does not move, I did no work, on the bolder. However if I push with much less force on a smaller rock and move it a long distance, I have done work. Work is Force times Distance.

W = F * D

When you factor in the time it took to move the rock that distance, you can calculate the Power require to do the Work. You can generate more Power by moving a light rock, a long distance, in a short time, verses moving a heavy rock, a short distance, over a long time.

Hp is the rotational equivalent to Work per unit of time, in linear motion.

So Torque, like force, accomplishes no work, if there is no rotation. When you pull on a wrench and the bolt does not turn, you have accomplished nothing. On the other hand, if you apply a Torque and the object rotates, you have done work, and when you factor in the time it took to rotate an angular distance, you can calculate the Power expended. Or in the case of an engine, the power generated.

So folks listen carefully here. You do not have to calculate the torque to the wheels in each gear at every rpm and graph it, to figure out which gear will give more acceleration at a given speed. If you know the Hp at every rpm (if you know the torque at every rpm then you know the Hp it is simple math) and you know what rpm you will run, in each gear, at a given speed, it is simple to calculate the Hp the engine will make, at a given speed, in each gear. Whichever gear allows the engine to make the most Hp, at that speed, is the gear that will accelerate the vehicle at the highest rate.

Maximizing Torque does not yield maximum acceleration! Maximizing Hp yields maximum acceleration! I cannot shout that loud enough. Hp is the measurement of work per unit of time. It is the the measurement that everyone is trying to figure out, but they do not understand it and ignore it!

Peak Hp always happens well past peak torque, at considerably less torque. Get your rpm at peak Torque in 4th gear, floor it and feel the acceleration. Now get your rpm at peak Torque in 4th gear again, only this time shift down to 3rd gear and floor it. Much more acceleration, right? Yep, and you accomplish it with the engine making less Torque, but more Hp. There's your proof. You've done it a thousand times.

Torque is just rotational force. If nothing moves, all the force in the world will do no work. Work moves your car from point "A" to point "B". Power is the distance per unit of time. If you want to get from point "A" to point "B" in less time, increase the Power. Hp is rotational Power. Folks they understood this in the 19th century. That is why they figured out how to calculate Hp in the first place. They wanted to compare the work a horse could do, to the work an engine could do. Here we are in the 21 century with every learning aid and google at you fingertips, and most people still do not get it.

You make some good points, however, just a bit misguided in the real world.

You see, our friend Uglug is much smarter than what we give him credit for in our story meant to substantiate a theory in the village of Internet. You see, he comes from a village called Reality. When he pushes on that big rock (mostly to impress the ladies) he quickly realizes that it isn’t moving and continuing along that path will most certainly result in an embarrassing stall. No, our friend Uglug stops pushing the big rock and picks up a smaller one, however, the smaller one is just too small to make best use of his genetic advantage (torque).

Uglug does some testing and finds the perfect size rock to allow him to bring the greatest tonnage to the top of the hill (peak horsepower), but upon looking at the quarry, he sees that there are very few rocks in his perfect size, he then has to evaluate which rock size range will give him best advantage over the little fast guys. Some are a bit smaller and some a bit bigger than his best size. This spread is what we hot rodders see as the spread between transmission gears. The smaller we keep that spread (close ratio tranny) then the better we will be able to perform work, but this quarry only has a wider spread available (street tranny) so Uglug must find the optimum range, not just the single optimum size.

Back to our reality. Unless running a CVT, we spend almost 100% of our time either above or below peak hp. The torque curve both before and after peak hp. combined with transmission spread tell us the optimal shift point for best acceleration. In real testing, peak hp will be found in every gear, you may hit it just after shifting or maybe just before shifting, or maybe in the middle. It all depends on the torque curve in that area. Does torque fall off quickly after peak? Maybe builds quickly to peak and then holds. Do you hit peak hp 100rpm before the rev limiter? Only the dyno can tell us everything we need to know.

That said, yes, you can get close calculating shift points with a single gear pull and math, but simply knowing peak will never be sufficient, you must know the curve. That said, consider that the single gear/math method completely eliminates factors such as MOI of rotating parts and differing frictional losses in each gear. You are already on the dyno, why would you bother with a math approximation when all you have to do is change gears and see the facts?

EDIT: Here is the factory dyno chart for my motor (MSTR). Note how torque falls off rapidly immediately after peak hp. My speculation is that this curve will require me to shift immediately after hitting peak hp, but with such a flat curve I won't know until I test.