Torque vs Horsepower - VERY impressive commentary

[Mac]

Welcome to the CAC, Nick. I have to say you've picked an unusual way to introduce yourself.

As for the rest of you, pull in the horns a bit. Nick is entitled to his opinion and explained his perspective. If you disagree with something factual he posted, feel free to engage in polite discourse and debunk factually but no "ad hominem" attacks.

-Mac

 

[Augie1]

The Plain Truth about Bruce Augenstein’s Explanation of Torque and Power
- Nick Papagiorgio

This article by Bruce Augenstein has been popped all over the web over the past decade or so, all by people who mean well, but who, like Augenstein, would not know a proper explanation of torque and power from a pile of horse manure if their lives depended on it...

Mr. Papagiorgio's post made me grin - although I must say his tone is both confrontive and disdainful. The fact is that he is not incorrect when he actually gets to facts instead of invective. For instance, at any given instant, power wins in terms of acceleration if all else is equal.

Fair enough - but there's more.

I wrote my original note on this topic back in late '93, if memory serves. It was a response in an internal corporate notes file in a very torque-centric discussion of power and torque. In that context, it was spot on, but somebody picked up that note and posted it on the vettnet site without permission, and it's since been copied on around a hundred web sites around the globe, and has been translated into at least four languages.

What makes me grin is that Mr. Papagiorgio thinks that he is the one true keeper of the definitions of torque and power, and all others are dunces. I am reminded of the story of the flea, floating down the river on a leaf, in an, ahem, excited condition, shouting for the bridge to open.

The fact is that my "article" has been referred to in terms of optional reading for university students in a physics 102 class, and I got a message from another university professor thanking me for making his job a little easier in terms of his physics 101 students. It's also been featured in the "Boston Bimmer" BMW club magazine.

I didn't even know that I was more or less famous until someone mentioned the vettenet site (and others), several years later. I then forwarded a revised version of that article to the vettnet site, with no response.

The original article is correct in every way, although obviously unique in the way information is presented on the topic. Mr. Papagiorgio will of course never agree, but here is the last (and best, in my opinion) version of that article, written about ten years ago, with significant updates from the original.

Horsepower and Torque - a Primer

There's been a certain amount of discussion, in this and other files, about the concepts of horsepower and torque, how they relate to each other, and how they apply in terms of automobile performance. I have observed that, although nearly everyone participating has a passion for automobiles, there is a huge variance in knowledge. It's clear that a bunch of folks have strong opinions (about this topic, and other things), but that has generally led to more heat than light, if you get my drift. This is meant to be a primer on the subject.

OK. Here's the deal, in moderately plain English.

Force, Work and Time

If you have a one pound weight bolted to the floor, and try to lift it with one pound of force (or 10, or 50 pounds), you will have applied force and exerted energy, but no work will have been done. Work requires movement. If you unbolt the weight, and apply a force sufficient to lift the weight one foot, then one foot-pound of work will have been done. If that event takes a minute to accomplish, then you will be doing work at the rate of one foot-pound per minute. If it takes one second to accomplish the task, then work will be done at the rate of 60 pound feet per minute, and so on.

In order to apply these measurements to automobiles and their performance (whether you're speaking of torque, horsepower, Newton meters, watts, or any other terms), you need to address the three variables of force, work and time.

A while back, a gentleman by the name of Watt (the same gent who did all that neat stuff with steam engines) made some observations, and concluded that the average horse of the time could work at a rate that would lift a 550 pound weight one foot in one second, thereby performing work at the rate of 550 pound feet per second, or 33,000 pound feet per minute. He then published those observations, and stated that 33,000 pound feet per minute of work was equivalent to the power of one horse, or, one horsepower.

Everybody else said okay.

For purposes of this discussion, we need to measure units of force from rotating objects such as crankshafts, so we'll use terms that define a twisting force, such as torque. A foot pound of torque is the twisting force necessary to support a one pound weight on a weightless horizontal bar, one foot from the fulcrum.

In fact, what standard engine dynamometers actually measure is torque (not horsepower) by using a resistance to hold the engine at a constant speed while at full throttle, and then measuring the resistance required to keep the engine from accelerating. Then we can calculate actual horsepower by converting the twisting force of torque into the work units of horsepower.

Here’s how:

Visualize that one pound weight we mentioned, one foot from the fulcrum on its weightless bar. If we rotate that weight for one full revolution against a one pound resistance, we have moved it a total of 6.2832 feet (Pi * a two foot circle), and, incidentally, we have done 6.2832 pound feet of work.

Okay. Remember Watt? He said that 33,000 pound feet of work per minute was equivalent to one horsepower. If we divide the 6.2832 pound feet of work we've done per revolution of that weight into 33,000 pound feet, we come up with the fact that one foot pound of torque at 5252 rpm is equal to 33,000 pound feet per minute of work, and is the equivalent of one horsepower. If we only move that weight at the rate of 2626 rpm, it's the equivalent of 1/2 horsepower (16,500 pound feet per minute), and so on. Therefore, the following formula applies for calculating horsepower from a torque measurement:

Torque * RPM
---------------- = Horsepower
5252

This is not a debatable item. It's the way it's done. Period.

The Case for Torque

Now, what does all this mean in car land?

First of all, from a driver's perspective, torque rules, to use the vernacular. Any given car, in any given gear, will accelerate at a rate that exactly matches its torque curve (allowing for increased air and rolling resistance as speeds climb). Another way of saying this is that a car will accelerate hardest at its torque peak in any given gear, and will not accelerate as hard below that peak, or above it. Torque is the only thing that a driver feels, and horsepower is just sort of an esoteric measurement in that context. 300 pound feet of torque will accelerate you just as hard at 2000 rpm as it would if you were making that torque at 4000 rpm in the same gear, yet, per the formula, the horsepower would be *double* at 4000 rpm. Therefore, horsepower tends to not be particularly meaningful from a driver's “belt in the back” perspective, and the two numbers only get friendly at 5252 rpm, where horsepower and torque always come out the same.

In contrast to a torque curve (and the matching push back into your seat), horsepower rises rapidly with rpm, especially when torque values are also climbing. Horsepower will continue to climb, however, until well past the torque peak, and will continue to rise as engine speed climbs, until the torque curve really begins to plummet, faster than engine rpm is rising. However, as I said, horsepower has nothing to do with what a driver feels.

You don't believe all this?

Fine. Take your non-turbo car (turbo lag muddles the results) to its torque peak in first gear, and punch it. Notice how the seat belted you in the back? Now take it to the power peak, and punch it. Notice that the belt in the back is a bit weaker? Okay. Now that we're all on the same wavelength (and I hope you didn't get a ticket or anything), we can go on.

Torque is What You Feel, but Horsepower Rules

So if torque is so all-fired important (and feels so good), why do we care about horsepower? Because (to quote a friend), "It's better to make torque at high rpm than at low rpm, because you can take advantage of gearing."

For an extreme example of this, I'll leave car land for a moment, and describe a waterwheel I got to watch a while ago. This was a pretty massive wheel (built a couple of hundred years ago), rotating lazily on a shaft that was connected to the works inside a flour mill. Working some things out from what the people in the mill said, I was able to determine that the wheel typically generated about 2600(!) pound feet of torque. I had clocked its speed, and determined that it was rotating at about 12 rpm. If we hooked that wheel to, say, the drive wheels of a car, that car would go from zero to twelve rpm of its drive wheels in a flash, and the waterwheel would hardly notice.

On the other hand, twelve rpm of the drive wheels is around one mile per hour for the average car, and, in order to go faster, we'd need to gear it up. If you remember your junior high school science classes and the topic of simple machines, you'll remember that to gear something up or down gives you linear increases in speed with linear decreases in force, or vice versa. To get to 60 miles per hour would require gearing the output from the wheel up by 60 times, enough so that it would be effectively making a little over 43 pound feet of torque at the output (one sixtieth of the wheel's direct torque). This is not only a relatively small amount; it's less than what the average car needs in order to actually get to 60. Applying the conversion formula gives us the facts on this. Twelve times twenty six hundred, over five thousand two hundred fifty two gives us:

6 horsepower.

OOPS. Now we see the rest of the story. While it's clearly true that the water wheel can exert a bunch of force, its power (ability to do work over time) is severely limited.

At the Drag Strip

Now back to car land, and some examples of how horsepower makes a major difference in how fast a car can accelerate, in spite of what torque on your backside tells you.

A very good example would be to compare the LT-1 Corvette (built from 1992 through 1996) with the last of the L98 Vettes, built in 1991. Figures as follows:

Engine--------------Peak HP @ RPM-------------Peak Torque @ RPM
L98---------------------250 @ 4000----------------------340 @ 3200
LT-1--------------------300 @ 5000----------------------340 @ 3600

The cars are essentially identical (drive trains, tires, etc.) except for the engine change, so it's an excellent comparison.

From a driver's perspective, each car will push you back in the seat (the fun factor) with the same authority - at least at or near peak torque in each gear. One will tend to feel about as fast as the other to the driver, but the LT-1 will actually be significantly faster than the L98, even though it won't pull any harder. If we mess about with the formula, we can begin to discover exactly why the LT-1 is faster. Here's another slice at that torque and horsepower calculation:

Horsepower * 5252
------------------- = Torque
RPM

Plugging some numbers in, we can see that the L98 is making 328 pound feet of torque at its power peak (250 hp @ 4000). We can also infer that it cannot be making any more than 263 pound feet of torque at 5000 rpm, or it would be making more than 250 hp at that engine speed, and would be so rated. In actuality, the L98 is probably making no more than around 210 pound feet or so at 5000 rpm, and anybody who owns one would shift it at around 46-4700 rpm, because more torque is available at the drive wheels in the next gear at that point. On the other hand, the LT-1 is fairly happy making 315 pound feet at 5000 rpm (300 hp times 5252, over 5000), and is happy right up to its mid 5s red line.

So, in a drag race, the cars would launch more or less together. The L98 might have a slight advantage due to its peak torque occurring a little earlier in the rev range, but that is debatable, since the LT-1 has a wider, flatter curve (again pretty much by definition, looking at the figures). From somewhere in the mid-range and up, however, the LT-1 would begin to pull away. Where the L98 has to shift to second (and give up some torque multiplication for speed, a la the waterwheel), the LT-1 still has around another 1000 rpm to go in first, and thus begins to widen its lead, more and more as the speeds climb. As long as the revs are high, the LT-1, by definition, has an advantage. As a practical matter, a typical L98 6-speed car might cover a quarter mile with an ET of around 14 seconds at around 99 or 100 mph, while the equivalent LT-1 will generally be at least a half second faster, at 104 – 105 mph. Mind you, as I’ve mentioned, the LT1 doesn’t pull any harder – just longer.

There are numerous examples of this phenomenon. The Acura RSX Type S, for instance, is faster than the garden variety RSX, not because it pulls particularly harder (it doesn't), but because it too pulls longer in each gear. It doesn't feel particularly faster, but it is.

A final example of this requires your imagination. Figure that we can tweak an LT-1 engine so that it still makes peak torque of 340 pound feet at 3600 rpm, but, instead of the curve dropping off to 315 pound feet at 5000, we extend the torque curve so much that it doesn't fall off to 315 pound feet until 15000 rpm. Okay, so we'd need to have virtually all the moving parts made out of unobtanium, and some sort of turbo charging on demand that would make enough high-rpm boost to keep the curve from falling, but hey, bear with me.

If you raced a stock LT-1 with this car, they would launch together, but, somewhere around the 60-foot point, the stocker would begin to fade, and would have to grab second gear shortly thereafter. Not long after that, you'd see in your mirror that the stocker has grabbed third, and not too long after that, it would get fourth, but you wouldn't be able to see that due to the distance between you as you crossed the line, still in first gear, and pulling like crazy.

I've got a computer simulation that models an LT-1 Vette in a quarter mile pass, and it predicts a 13.38 second ET, at 104.5 mph. That's pretty close (actually a bit conservative) to what a stock LT-1 can do at 100% air density at a high traction drag strip, being power shifted. However, our modified car, while belting the driver in the back no harder than the stocker (at peak torque) does an 11.96, at 135.1 mph - all in first gear, naturally. It doesn't pull any harder, but it sure as heck pulls longer. It's also making 900 hp, at 15,000 rpm.

Of course, looking at top speeds, it's a simpler story...

At the Bonneville Salt Flats

Looking at top speed, horsepower wins again, in the sense that making more torque at high rpm means you can use a stiffer gear for any given car speed, and have more effective torque (and thus more thrust) at the drive wheels.

In fact, operating at the power peak means you are accelerating the absolute best you can at any given car speed, measuring torque at the drive wheels. I know I said that acceleration follows the torque curve in any given gear, but at any given car speed, horsepower is the absolute governor of how fast you can accelerate. This means that at any given instant, it's power that determines how fast you can accelerate, and not torque. In fact, horsepower is a kind of shorthand in this context. No matter what gear you’re in or what the final drive ratio is, more power at that speed means more acceleration because you’ll have more torque at the drive wheels. I'll use a BMW example to illustrate this:

At the 4250 rpm torque peak, a 3-liter E36 M3 is doing about 57 mph in third gear, and, as mentioned previously, it will pull the hardest in that gear at that speed when you floor it, discounting wind and rolling resistance. In point of fact (and ignoring both drive train power losses and rotational inertia), the rear wheels are getting 1177 pound feet of torque thrown at them at 57 mph (225 pound feet, times the third gear ratio of 1.66:1, times the final drive ratio of 3.15:1), so the car will bang you back very nicely at that point, thank you very much.

However, if you were to re-gear the car so that it is at its power peak at 57 mph, you’d have substantially more torque at the drive wheels. You'd have to change the final drive ratio to approximately 4.45:1 in order to do this, but with that final drive ratio installed, you'd be at 6000 rpm in third gear at 57 mph, where the engine is making 240 hp. Going back to our trusty formula, you can ascertain that the engine is down to 210 pound feet of torque at that point (240 times 5252, divided by 6000). However, doing the arithmetic (210 pound feet, times 1.66, times 4.45), you can see that you are now getting 1551 pound feet of torque at the rear wheels, making for a nearly 32% more satisfying belt in the back.

Any other rpm (other than the power peak) at a given car speed will net you a lower torque value at the drive wheels. This would be true of any car on the planet, so, you get the best possible acceleration at any given vehicle speed when the engine is at its power peak, and, theoretical "best" top speed will always occur when a given vehicle is operating at its power peak.

Force, Work and Time

At this point, if you're getting the idea that work over time is synonymous with speed, and as speed increases, so does the need for power, you've got it.

Think about this. Early on, we made the point that 300 pound feet of torque at 2000 rpm will belt the driver in the back just as hard as 300 pound feet at 4000 rpm in the same gear - yet horsepower will be double at 4000. Now we need to look at it the other way: We NEED double the horsepower if we want to be belted in the back just as hard at twice the speed. As soon as we factor speed into the equation, horsepower is the thing we need to use as a measurement. It's a direct measure of the work being done, as opposed to a direct measure of force. Although torque and horsepower are obviously related (and each in a sense a function of the other), a good way to think about this is that torque determines the belt in the back capability, and horsepower determines the speed at which you can enjoy that capability. Do you want to be belted in the back when you step on the loud pedal from a dead stop? That's torque. The water wheel will deliver that, in spades. Do you want to be belted in the back in fourth gear at 100 down the pit straight at Watkins Glen? You need horsepower. In fact, ignoring wind and rolling resistance, you'll need exactly 100 times the horsepower if you want to be belted in the back just as hard at 100 miles per hour as that water wheel belted you up to one mile per hour.

Of course, speed isn't everything. Horsepower can be fun at antique velocities, as well...

"Modernizing" The 18th Century

Okay. For the final-final point (Really. I Promise.), what if we ditched that water wheel, and bolted a 3 liter E36 M3 engine in its place? Now, no 3-liter BMW is going to be making over 2600 pound feet of torque (except possibly for a single, glorious instant, running on nitromethane). However, assuming we needed 12 rpm for an input to the mill, we could run the BMW engine at 6000 rpm (where it's making 210 pound feet of torque), and gear it down to a 12 rpm output, using a 500:1 gear set. Result? We'd have *105,000* pound feet of torque to play with. We could probably twist the entire flour mill around the input shaft, if we needed to.

The Only Thing You Really Need to Know

For any given level of torque, making it at a higher rpm means we increase horsepower - and now we all know just exactly what that can do for us, don't we? Repeat after me: "It's better to make torque at high rpm than at low rpm, because you can take advantage of gearing."

Thanks for your time.

Bruce

 

[Toms007]

Augie1, thank you so much for stepping in here and clarifying your article. I do hope that you hang around a while.

 

[Yoda]

Welcome to the Corvette Action Center Community

At my age and mind set I apologize... I did not read every word you wrote, I more or less glanced through your writing... Nicely done, Your professional demeanor and approach is to be commended, in light of the reason...

Hopefully you can and will stay around and visit all the portal's we offer here in our Community. I think you might find a lot of it very interesting. Our Webmaster/Owner has a lot of heart and soul in the Action Center. I doubt seriously that you will find another Corvette Site with as much information and for the most part friendly forums

Thanks for your response and doing so in an informative and professional way.

Bud Dougherty
Forums Administrator

 

[Tuna]

After reading all this, it still sounds like what I said earlier: Torque accelerates the vehicle and HP controls top speed.

 

[Augie1]

After reading all this, it still sounds like what I said earlier: Torque accelerates the vehicle and HP controls top speed.

Torque does indeed accelerate the vehicle - but horsepower governs how fast a vehicle will accelerate at any given speed, and how fast it will get to another speed.

Bruce

 

[Remo]

Torque and Recoil

Two of my favorite subjects. Corvettes and large caliber weapons.:L

 

[Nick Papagiorgio]

More patently dishonest conduct from Bruce Augensteinthis

Mr. Papagiorgio's post made me grin - although I must say his tone is both confrontive and disdainful. The fact is that he is not incorrect when he actually gets to facts instead of invective. For instance, at any given instant, power wins in terms of acceleration if all else is equal.

That's preposterous, and it is patently dishonest. But as for being disdainful, I have no qualms about stating openly that I absolutely do have contempt and disdain for you. The reason I feel this way is that it is manifest to me that you have no predisposition for fundamentally honest behavior. It is manifest to me that the opposite is true.

Fair enough - but there's more.

I wrote my original note on this topic back in late '93, if memory serves. It was a response in an internal corporate notes file in a very torque-centric discussion of power and torque. In that context, it was spot on, but somebody picked up that note and posted it on the vettnet site without permission, and it's since been copied on around a hundred web sites around the globe, and has been translated into at least four languages.

There has never been anything about your article that was "spot on", no matter the context. It has always been predominately a pile of specious nonsense with a smidgen of correct fact sprinkled in. At this stage, you surely must know this as well as I, but you continue to deny what you yourself must surely know to be true. It must be really tough living with that.

What makes me grin is that Mr. Papagiorgio thinks that he is the one true keeper of the definitions of torque and power, and all others are dunces. I am reminded of the story of the flea, floating down the river on a leaf, in an, ahem, excited condition, shouting for the bridge to open.

I have no idea what makes you grin, and I could not care less. What I do know, and care about, is that the would-be explanation that you wrote is specious nonsense. It is not remotely a correct explanation of torque and power. By and large, notwithstanding that you included some correct fact, it is a pile of garbage. Anyone who doubts this need only read what I wrote, and assuming that they are capable of rational thought, this is the conclusion that they will reach. I do not need to repeat what I wrote. I stated the case succinctly, and anyone who is open-minded and capable of rational thought will reach the same conclusion that I reached. Of course many people will not, but to a great extent that is only because over the many years that have passed since your specious article first appeared on the Internet, many people have had their heads filled with your nonsense. That is the very motivation for my writing the refutation.

The fact is that my "article" has been referred to in terms of optional reading for university students in a physics 102 class, and I got a message from another university professor thanking me for making his job a little easier in terms of his physics 101 students. It's also been featured in the "Boston Bimmer" BMW club magazine.

I am aware of one instance of an instructor of some sort referring his students to your article. As I recall, he was located in Australia or New Zealand, but I'm not certain. It is really unfortunate and sad that he did so. I believe that was corrected after I contacted him and showed him the correct interpretation of what you wrote. Regardless, if you are aware of any university or college or high school instructors of physics who are still doing this, I implore you to identify them to me so that I can contact them and enlighten them. Occasionally even instructors get their heads screwed on the wrong way, but usually it doesn't take much effort to get them pointed in the right direction.

The original article is correct in every way, although obviously unique in the way information is presented on the topic. Mr. Papagiorgio will of course never agree, but here is the last (and best, in my opinion) version of that article, written about ten years ago, with significant updates from the original.

The article is exactly what I said it was, for the precise reasons that I explained. The version that I read, and to which my refutation applies, is the very version that you included. It is garbage of the highest order, for the reasons that I already have explained very succinctly and very clearly. Anyone who doubts this need only read what I wrote, and assuming that they are possessed of a decent capability for reason and reading comprehension, they will conclude that what you wrote is predominately nonsense.

I see where you took out the part where you wrote, "no one on the planet ever measures power". But you are very, very stubborn. You still insist that "what standard engine dynamometers actually measure is torque". This is every bit as specious as before, and at this point it becomes disingenuous to boot, because at this point you surely must realize that this is nothing more than a silly contrivance. What exactly constitutes a "standard dynamometer"? And what exactly is your definition of "actually measure"? There is no such thing as a "standard dynamometer". This is just something that you made up, just like your understanding of torque and power. And the notion of "actually measure" implies, logically, that some measurements are not "actual". I defy you to provide a non-contrived, straightforward definition, i.e., the criteria by which some measurements are "actual" whereas other measurements are not actual. EVERYONE WHO HAS EVER ACTUALLY STUDIED PHYSICS AT THE COLLEGE LEVEL AND WHO GOT THE BASIC CONCEPTS STRAIGHT IN HIS OR HER HEAD KNOWS PERFECTLY WELL THAT THIS NOTION IS ENTIRELY CONTRIVED. It is entirely contrary to the basic tenets of the philosophy of science, and this is something everyone who knows anything at all about the philosophy of science knows perfectly well. And even from the perspective of applied practice, what you claim simply is not true. There are practical dynamometers, of the brake dynamometer variety, where power is deduced from measurements of temperature/heat or electrical measurements, where the determination of power is in no way predicated on the determination of torque. And when measurements of torque are obtained, this generally involves a calculation taken with measurements of distance and force. This notion that you have, about torque being "actually" measured and power derived, is just something that you came up with because in your mind, you think of torque as being tangible and power being some sort of abstraction. It is a notion that you concocted then, and it remains nothing more than a concoction.

Here is another perfectly good example of where it is evident that you do not understand elementary physics in the least:

If you have a one pound weight bolted to the floor, and try to lift it with one pound of force (or 10, or 50 pounds), you will have applied force and exerted energy, but no work will have been done. Work requires movement. If you unbolt the weight, and apply a force sufficient to lift the weight one foot, then one foot-pound of work will have been done. If that event takes a minute to accomplish, then you will be doing work at the rate of one foot-pound per minute. If it takes one second to accomplish the task, then work will be done at the rate of 60 pound feet per minute, and so on.

You said that in this case where the where the weight does not move, that you will have exerted energy but no work will have been done. Now, I did not make a big deal of this in my refutation, because it would have been a distraction to have done so, because this is not the reason per se that your article is nonsense. But it does reveal quite plainly that you have never, ever actually studied physics beyond possibly some class you took in high school at most. The reason is that no one who has ever actually studied physics and who understood one whit of it would ever, ever say that energy had been exerted when no work had been performed. The equivalence between energy and work is something that you learn very early on, and once you learn that, you would never, ever be caught dead saying or implying anything to the contrary, for fear for that the professor would toss you out on your head. This is a real error, and is one that no one who has every actually studied elementary physics would ever, ever make. Similarly, no one who has ever really studied Newtonian physics would ever use the word force in the way that you did. You spoke of the force sufficient to lift the weight a specific distance, which of course implies equivalency between force and work. This is sloppy and manifestly contrary to the fact that work equates to force multiplied by distance. No person who has ever actually studied physics would ever, ever make that error.

But I need to reiterate: these errors are not the major errors with which I am concerned. I am concerned with the fact that the overall understanding that you expounded for torque and power is preposterous. I have already explained all that. I point out these errors because I think it is relevant that you have never actually studied physics, and this is something that I think needs to be pointed out in a plain manner to anyone who is interested in this.

At this point, if you're getting the idea that work over time is synonymous with speed, and as speed increases, so does the need for power, you've got it.

This kind of stuff just makes me cringe, and it surely will have the same effect on anyone who truly understands physics. "work over time is synonymous with speed"? What in the h*ll does that even mean? Like the majority of what you wrote, it has no real correlation to any substantively correct understanding of physics. It is jabberwocky. "work over time" presumably means instantaneous power, but power equates to acceleration divided by the product of mass and velocity. This just doesn't make a whit of sense. It is jabberwocky. But again, the real problem with the article is with the overall understanding that you expounded, particularly with respect to the notions about the significance of power and the lack of a direct, linear connection between power and the force that you sense "on your backside".

Think about this. Early on, we made the point that 300 pound feet of torque at 2000 rpm will belt the driver in the back just as hard as 300 pound feet at 4000 rpm in the same gear - yet horsepower will be double at 4000. Now we need to look at it the other way: We NEED double the horsepower if we want to be belted in the back just as hard at twice the speed. As soon as we factor speed into the equation, horsepower is the thing we need to use as a measurement. It's a direct measure of the work being done, as opposed to a direct measure of force.

Now that, I believe, is something that you added later. I'm not sure, even though you were on the right track here and struggling to find a way to say something that is substantively correct, you went and made a complete mess of it, because of this:

Although torque and horsepower are obviously related (and each in a sense a function of the other), a good way to think about this is that torque determines the belt in the back capability, and horsepower determines the speed at which you can enjoy that capability. Do you want to be belted in the back when you step on the loud pedal from a dead stop? That's torque. The water wheel will deliver that, in spades. Do you want to be belted in the back in fourth gear at 100 down the pit straight at Watkins Glen? You need horsepower.

THIS IS COMPLETE, UTTER, TOTAL CRAP!!!! IT IS GARBAGE!!!! THERE IS NOT ONE IOTA OF TRUTH TO THIS. IT BEARS NO SUPERFICIAL SIMILARITY TO THE CORRECT UNDERSTANDING OF THE BASIC PHYSICS THAT YOU ATTEMPT TO EXPLAIN BUT THAT YOU DO NOT UNDERSTAND IN THE LEAST!!!! YOU ARE TEACHING PEOPLE NONSENSE, AND THIS IS THE PLAIN, SIMPLE TRUTH OF THE MATTER!!!!!

THE "BELT IN THE BACK CAPABILITY" REFERS TO ACCELERATION, AND ACCELERATION AT ANY INSTANT (ANY!!!) EQUATES TO ACTUAL POWER DIVIDED BY THE PRODUCT OF MASS AND VELOCITY!!! SAID DIFFERENTLY, THE VALUE OF ACCELERATION AT ANY INSTANT MAY BE FOUND BY MULTIPLYING ENGINE TORQUE BY ENGINE SPEED, AND THEN DIVIDING BY THE PRODUCT OF MASS AND VELOCITY!!! EVEN IF YOU NORMALIZE MASS AND VELOCITY TO STANDARD, AGREED UPON VALUES, IT IS STILL IS NOT THE LEAST BIT CORRECT TO EQUATE ACCELERATION WITH ENGINE TORQUE!!!! THIS IS NONSENSE!!!!!!!!


Bruce Augenstein, your article contains some correct fact, no question about it. But that does not make it a correct article. It is the biggest pile of unmitigated garbage that I have ever encountered in my life. It is just plain old garden variety garbage, pure and simple. You can deny this to your heart's content, but it won't change the fact that it is crap, and I have no qualms about saying so.

 

[1963SS]

Play nice gentlemen. This is getting really technical and above the heads of many on this forum. I have read some good points on both sides of the disagreement. Here in Kentucky we try to keep it simple. If torque was the almighty predictor then a 6.7 liter Cummins Dodge would destroy a ZR1 Corvette. The Cummins makes upwards of 800 ft/lbs and the lowly 6.2 liter Chevy only makes around 600 ft/lbs. So I think we can forget about torque alone. I think the best momentary acceleration would occur at the peak torque of an engine. That would be why, IMHO, that a 7 speed gearbox will generally outperform a 4 speed. The engine can stay closer to it's torque peak for a longer period of time.

As I recall, acceleration is equal to force divided by mass. That is why a vehicles horsepower to weight ratio is a good indicator of the acceleration potential. On a road racing course with many turns a vehicle with more torque will probably beat a car with more horsepower. Acceleration will be quicker and acceleration is dependent on torque . Now on a drag race car or something like NASCAR the horsepower will probably win that race. There's not as much acceleration required but the power is necessary to push the frontal area and friction components to a higher speed is needed.

In a perfect world with no friction a CVT equipped car that ran at it's torque peak continuously would out accelerate the same car that used a standard transmission. That is why engine designers try to achieve as broad a torque band as possible. I'm not an argumentative sort but a pretty good automobile designer named Enzo Ferrari once said that "Horsepower sells cars while Torque wins races." He was hopefully making his statement on the assumption that both cars had plenty of both and also talking about Ferrari's forte.......road racing. I would not presume to argue with him.

And where did the torque indicator (pound/feet) come from anyways. It's confusing since the term has two different accepted meanings for different properties, one is a unit of work (a scalar quantity) and the other is a moment of a force (a vector quantity). Silly....IMHO. Auto manufacturers rate an engine at peak torque which is also silly. There should be some way to rate the engine at average torque over a given powerband. Although a flywheel doesn't add torque or horsepower it can certainly affect the 60 foot time which will affect the trap speed. There are just too many variables to get angry at each other over what I see as basically semantics.

If necessary, we need to discuss this with cooler heads and we need to omit, whenever possible, all the silly symbols and statements.The full-throttle behavior of an engine can be approximately modeled as a device which has some function [FONT=MathJax_Math]τ[/FONT][FONT=MathJax_Main]([/FONT][FONT=MathJax_Math]ω[/FONT][FONT=MathJax_Main])[/FONT] associated with it. This fixes the torque it can produce as a function of engine speed (rpm). This function is not at all constant, although engineers often strive to make it as flat as possible.

Regardless, given the torque function, there is an associated power [FONT=MathJax_Math]P[/FONT][FONT=MathJax_Main]([/FONT][FONT=MathJax_Math]ω[/FONT][FONT=MathJax_Main])[/FONT][FONT=MathJax_Main]=[/FONT][FONT=MathJax_Math]ω[/FONT][FONT=MathJax_Math]τ[/FONT][FONT=MathJax_Main]([/FONT][FONT=MathJax_Math]ω[/FONT][FONT=MathJax_Main])[/FONT]. So if the torque is known at all speeds, the power is known at all speeds (and vice versa). You can't have one without the other. Remember, Modern transmissions have many closely-spaced ratios, so except at very low speeds (at the bottom of 1st gear), an engine may be kept close to its power peak for as long as desired. That means that a well-designed car that is driven well may produce a force [FONT=MathJax_Math]F[/FONT][FONT=MathJax_Main]∼[/FONT][FONT=MathJax_Math]P[/FONT][FONT=MathJax_Main]p[/FONT][FONT=MathJax_Main]e[/FONT][FONT=MathJax_Main]a[/FONT][FONT=MathJax_Main]k[/FONT][FONT=MathJax_Main]/[/FONT][FONT=MathJax_Math]v[/FONT]. This depends only on the peak power (and velocity), and explains why the power-to-weight ratio is such a good predictor of acceleration performance as I mentioned earlier.

Having said that, the torque peak is not completely irrelevant. Its position relative to the power peak is usually a good indicator of the size of the car's "powerband." Essentially, how high do you have to rev it in a given gear before the engine really gets going? Having a wide powerband is extremely important in everyday (or moderately aggressive) driving where you're not going to redline in every gear. It makes the car feel much more powerful even if the maximum performance is the same. God, I love Google and I am able to talk about this in normal language even though I graduated from MIT with a degree in Physics in 1973. I earned my Doctorate in 1980. Wanna Dance?:L

Whenever I build an engine for a customer I strive to keep the torque band broad and I will not over cam an engine. I've lost some work because I won't do what the potential customer wants. The old saying that the customer is always right is always wrong. They have no idea and I'll not compromise an engine or it's driveability based on a whim from some one that doesn't know very much at all. I have many 500 FWHP engines that are daily drivers and some are over a hundred thousand miles. It can be done and done easily. Torque and horsepower are matched to gear ratios and if done properly they will drive great and even surpass some cars that have more horsepower. It's more complicated than just bolting some parts together. Of course, as always, that just IMHO.

 

[Mac]

It appears "Nick Papagiorgio" has a bit of an obsession thing going on.

A gentle word of advice, Nick... Your arguments would be far more palatable and far less likely to get you banned from the CAC if you spent more time focusing on refuting Augie1's points with facts rather than posting angry yet somehow descriptive rhetoric.

-Mac

 

[TedC]

Here is how I approach this discussion (debate)...
The reason I prefer a V6 over a 4 cylinder is torque, not HP.
The reason I prefer a V8 over a V6 is torque, not HP.
The reason a L98 is quicker off the line than an LT1 is torque, not HP (better low RPM torque).
The reason an LT1 is faster after the first 1/8 mile is torque, not HP (better high RPM torque).
HP ratings are misleading indicators of performance. L98 with 3.07 and auto screams off the line. Traction remains my biggest enemy. My Ford Escape has a 3.0 V6 rated at 240 HP with a six speed auto. I would of much preferred a larger V6 with a lower rated HP but more usable low end torque.

 

[Nick Papagiorgio]

Thereby demonstrating that there is no hope for the future of mankind.

After reading all this, it still sounds like what I said earlier: Torque accelerates the vehicle and HP controls top speed.

As I have attempted to explain, this notion is nonsensical. I will try once more to explain why, and this time I will take a somewhat different approach.


You are venturing into the territory of causality. This is territory where learned physicists with PhD degrees do not tread lightly, for good reason. The reason is that when experiments are performed toward the goal of proving or disproving hypotheses, those experiments are capable of demonstrating the extent to which a given analytical formula describes the manner in which the phenomena relate to one another. But the experimental methods of science, together with the essential mathematical tools, are not themselves concerned with causality per se. This is something that all bona fide scientists understand perfectly well.


ALL statements and claims of the sort that distinguish or differentiate torque from power on the basis of individual phenomena that are purportedly attributable expressly to one vs. the other, i.e., “torque is what does X, and power is what does Y”, or “X is what torque does, whereas Y is what power does”, ARE CATEGORICALLY NONSENSICAL. It is simply is not possible to isolate torque and power each from the other such that certain specific effects are attributable more to one than the other. This notion simply does not make one whit of sense. It does not make one iota of sense. It does not make one scintilla of sense. Zilch. Nada. Not one solitary atom, speck, bit, trace, ounce, shred, crumb, fragment, grain, drop, spot, modicum, hint, smidgen of correct sense does this notion make.


There is only one notion that I know of that has any appreciable similarity to the sort of thing that you claim. It makes perfect sense to talk of how you go about maximizing some quantity, and to talk of which independent variable you have to maximize when your goal is to maximize some given, well-known, well-understood quantity. The notion of maximization, in contrast with the notion that you have fixated on, makes absolutely perfect sense. Scientists and engineers deal perpetually with the notion of maximization, but the ones who truly understand science rarely ever venture into the notion of causality per se. As it applies the subject at hand, it makes absolutely perfect sense to talk about how you go about maximizing acceleration. And whenever you talk about maximizing acceleration, you are talking about maximizing acceleration instantaneously. This is intrinsically true, because intrinsically, acceleration is an instantaneous quantity. Even if you talk about maximizing overall acceleration over some interval of time or distance, or from some initial speed to some target speed, you still are intrinsically talking about the instantaneous maximization of acceleration.


To maximize acceleration at any instant, you have to maximize power, not engine torque per se. This is an absolute, unyielding fact. Moreover, this particular fact is the true essence of the proper, substantive understanding of this subject, notwithstanding that Bruce Augenstein still has not figured out even this much about this subject. This fact about maximization of acceleration underlies the strategy for optimal gear selection. If you want to understand optimal gear selection, you have to understand this fact about instantaneous maximization of acceleration. To maximize wheel torque at any given, arbitrary instant, it is absolutely necessary to maximize power, not engine torque per se. Except for the loss of energy to friction, power is the same at the wheel as at the engine. Except for the loss to friction, the product of torque and rotational speed at the wheel is the same as the product of torque and rotational speed at the engine. As such, it is manifest that wheel torque at any given, arbitrary instant equates nominally (ignoring friction) to engine power divided by wheel rotational speed at that instant. At any given instant, wheel rotational speed is what it is, and to maximize acceleration at that instant, you maximize engine power, not engine torque per se. This is true at each and every instant.


THESE FACTS ARE THE TRUE ESSENCE OF THE SUBSTANTIVE AND CORRECT UNDERSTANDING OF THIS SUBJECT. These are the facts that Augenstein would need to have explained correctly and succinctly, in order for his purported explanation to qualify as a correct explanation. But he barely managed to vaguely allude to these facts, and did so only in a very discombobulated manner. Instead, he devoted the bulk of the article to specious nonsense, repeatedly asserting that torque is the only thing a driver feels, that power is meaningless as far as a driver is concerned, that greater power yields the ability to “pull longer” and not the ability to “pull harder”, that no one on the planet actually measures power. All of this is just a bunch of hogwash. The bulk of his article is fully devoted to expounding ideas that simply do not make one whit of sense. It is difficult to even extract palpable meaning from most of it, and once you have arrived at the palpable meaning that is implicit in what he wrote, the meaning that you find yourself pondering is something that does not make a whit of sense. Notwithstanding that he mixed a fair amount of correct fact in for good measure. By and large, the ideas that he expounded are quite simply nonsense.

 

[Nick Papagiorgio]

Here is how I approach this discussion (debate)...
The reason I prefer a V6 over a 4 cylinder is torque, not HP.
The reason I prefer a V8 over a V6 is torque, not HP.
The reason a L98 is quicker off the line than an LT1 is torque, not HP (better low RPM torque).
The reason an LT1 is faster after the first 1/8 mile is torque, not HP (better high RPM torque).
HP ratings are misleading indicators of performance. L98 with 3.07 and auto screams off the line. Traction remains my biggest enemy. My Ford Escape has a 3.0 V6 rated at 240 HP with a six speed auto. I would of much preferred a larger V6 with a lower rated HP but more usable low end torque.

The best way for me to approach this sort of thing is probably to say that there are two fundamentally distinct things being talked about.

One the one hand, there is the area where we endeavor to identify practical correlations between the peak values, of engine torque and power, and the meaningful performance characteristics that we appreciate and identify with, so that we can get a sense, from the peak values that we see, of what sort of performance a particular engine is likely to display. Everyone does this sort of thing. I do it all the time. But it is a seat-of-the-pants sort of thing. This sort of thing is not at all the same as a substantive, technically exact, quantitative analysis that endeavors to establish and describe the way in which engine torque and power relate in an exact, substantive, quantitative manner to acceleration.

Any substantive, quantitatively exact treatment of torque, power, and acceleration necessarily revolves around the manner in which these physical quantities are interrelated, instantaneously in time. This is intrinsically true. It is self-evident, because the physical quantities themselves are defined instantaneously in time. Anyone who endeavors to write an article of the sort that Bruce Augenstein wrote absolutely must understand this. But it is apparent that he simply did not understand this much.

And as for the other, less exact, less absolute perspective, the inherent problem is that it is not absolute or exact. But I do the same thing that you are talking about, and I do it habitually. When I see torque and power numbers quoted for an engine, I look immediately at the peak torque number, because I care about low-rpm performance and I know that peak torque tells me a little more about low-rpm performance than peak power is likely to tell me. But when I do this, I am constantly aware that this is all very crude. I always look at the rpm where the torque peak occurs, because if it occurs at very high rpm, I know that it isn't really going to tell me much at all about the low-rpm performance. The torque peak on many engines occurs above the midpoint of the operating range. And above and beyond that awareness that I keep in mind, I do not ever let myself get carried away with this to the point that I would start equating "torque" with low-rpm performance expressly. Most people do this casually, but most people have not subjected themselves to the sort of disciplined thought-process-realignment that occurs when you study physics at the college level. If everyone subjected themselves to that experience, then very few people would use the word "torque" in the manner than it is most commonly used. When the word "torque" is used in a fully substantive manner, there isn't anything that suggests that low-rpm performance is any more about torque than power. And there isn't anything that suggests that torque has greater significance at low-rpm than at high-rpm. When the word "torque" is used that casual manner, effectively as a synonym for low-rpm performance, there is implicit denial of the fact that torque is absolutely essential at high rpm, lest there be no power at high rpm and nothing else to be observed at high rpm that would be of interest to anyone. And there is likewise implicit denial of the fact that the full and complete measure of engine performance at any rpm is the power at that rpm, and not torque per se, unless alongside the value of torque you also stipulate the rpm, in which case you are in effect stipulating the power.

You also imply correlations between the sort of performance ("torque" vs. "power") and the quantity of cylinders in the engine. At this stage, there are multiple contrivances that bind up in a way such that it is futile to attempt to unravel it.

 

[Nick Papagiorgio]

Torque does indeed accelerate the vehicle - but horsepower governs how fast a vehicle will accelerate at any given speed, and how fast it will get to another speed.

Bruce

Again, you use language and phrasing that is abhorrent to anyone who is formally trained in the subject that you purport to understand. I do not expect that I would ever, ever hear any bona fide physicist say something along the lines of "torque accelerates a vehicle". A bona fide physicist would say something meaningful and precise about the manner in which torque and acceleration are related, instantaneously. But to the extent that it makes sense to say exactly what you said, it makes EVERY BIT AS MUCH SENSE to say "power accelerates a vehicle". The first part of that statement, pertaining expressly to torque, does not actually say anything beyond the fact that you can't have acceleration unless there is engine torque. That is the sum total of what that portion of that statement says.

And as to the other part of the statement, that horsepower "governs" how fast a vehicle will accelerate at any given speed, what exactly is meant by the word "govern"? Unless the meaning is made perfectly clear, the statement itself has no palpable meaning. A true physicist would be more specific, more precise, to insure that what they said actually had palpable meaning. A true physicist would have said something more like this: "For a given speed and mass, acceleration at any given instant is linearly determined by actual power at that instant, and therefore depends just as much on engine speed as on engine torque."

 

[Nick Papagiorgio]

It appears "Nick Papagiorgio" has a bit of an obsession thing going on.

A gentle word of advice, Nick... Your arguments would be far more palatable and far less likely to get you banned from the CAC if you spent more time focusing on refuting Augie1's points with facts rather than posting angry yet somehow descriptive rhetoric.

-Mac

The first meaning of the word "rhetoric" is simply that of command of the language. To the extent that I may happen to have that quality, it isn't something that I would expect anyone to criticize me for. But I don't think that's what you meant. The second meaning is that of pomposity, but here subjectivity comes into play. It may be that you, like many others, were taken in by what Augenstein had written, and that you are put off by someone having the audacity to tell you that most of it does not actually make sense. If this happens to be correct (it might not be), you consequently might not be as unbiased as you might otherwise be. Even if that isn't the case (it might not be, and I don't assume that it is) you still are likely influenced by the fact that I have made a bunch of people angry. That isn't something that I could have avoided except by remaining entirely silent. And speaking of anger, the strongest anger that has been displayed here has not come from me. Nor by Augenstein, and in the interest of following my mother's advice and finding something nice to say, I will point out that as concerns Augenstein, there is no evidence of irascibility. (Had to look that one up ...) That said, I respectfully will remind you of this:

Mr. Papagiorgio's post made me grin - although I must say his tone is both confrontive and disdainful.
...

What makes me grin is that Mr. Papagiorgio thinks that he is the one true keeper of the definitions of torque and power, and all others are dunces. I am reminded of the story of the flea, floating down the river on a leaf, in an, ahem, excited condition, shouting for the bridge to open.

Bruce

This is one of the least appropriate comments that has been made here, probably the least appropriate of any. It has no connection to anything that is real or actual, not even with respect to any real, actual conduct that I might have displayed. By intent it is a personal insult, purely for the sake of the insult, and like most insults that are designed by people with particular skill at that sort of thing, the target of the insult finds no easy way to respond. I do not possess that skill, i.e., the skill of designing insults of that sort. I lack that skill because I simply do not think in that manner. If I insult someone, there is no express intent to insult for the sake of the insult. When I insult someone, it is because I have said something that was obvious to me and that I thought needed to be said in a plain, straightforward manner.

 

[TedC]

Nick,
I'm trying to understand this better. So on a dyno, do we measure torque not HP? Then we apply a formula that factors in RPM to calculate HP. Is that correct? If so, then HP and torque are directly related (pretty much the same thing). I should then modify my prior statement to say:
The reason I prefer a V6 over a 4 cylinder is better torque and calculated HP at lower RPMs
The reason I prefer a V8 over a V6 is better torque and calculated HP at lower RPMs
The reason a L98 is quicker off the line than an LT1 is more low RPM torque or calculated HP
The reason an LT1 is faster after the first 1/8 mile is more upper RPM torque or calculated HP

My first car had a 400 CI mopar engine. I made a big mistake and swapped out the stock manifold for a single plane. This mod did indeed increase the upper end power. However, I lost the ability to spin the tires from a dead stop, but could now chirp the tire from 1st to 2nd. What I learned was the importance of low end torque (or low end calculated HP). For a street driver, I prefer the design point to be jack rabbit acceleration vs. top speeds.

 

[Rob]

Again, you use language and phrasing that is abhorrent to anyone who is formally trained in the subject that you purport to understand....

Which leads me to the question, and forgive me if I missed it somewhere along the way in the middle of this trainwreck of a thread...what exactly is your occupation and experience with the subject of this thread?

You can preach to me all you want about what is and isn't fact....but unless you have the credentials to back up your statements - your words hold as much value to me as the rest of the posts in this thread.

 

[Rob]

Oh....and while I'm at it....here's an article written by Jim Ingle, a retired GM engineer, who worked in Corvette Development since I believe, the early to mid seventies, and was responsible for establishing all of the Corvette's performance numbers:

Corvette Action Center | Tech Center | Horsepower vs. Torque

 

[Nick Papagiorgio]

Play nice gentlemen. This is getting really technical and above the heads of many on this forum. I have read some good points on both sides of the disagreement. Here in Kentucky we try to keep it simple. If torque was the almighty predictor then a 6.7 liter Cummins Dodge would destroy a ZR1 Corvette. The Cummins makes upwards of 800 ft/lbs and the lowly 6.2 liter Chevy only makes around 600 ft/lbs. So I think we can forget about torque alone. I think the best momentary acceleration would occur at the peak torque of an engine. That would be why, IMHO, that a 7 speed gearbox will generally outperform a 4 speed. The engine can stay closer to it's torque peak for a longer period of time.

You started off very good, i.e., the stuff about torque not being all there is to it. But then you said that the best momentary acceleration would occur at the torque peak of an engine. This is actually a more tenable statement than much of the other stuff that I read, because it has a clear, palpable meaning, that, in a definitive manner, either is or is not correct. Unlike the majority of statements found elsewhere, there is no likelihood that two different people would interpret your meaning differently. So I commend you for that. And for that, I will try to show respect, and hope to do so, when I point out, as I must, that the statement is not correct. In fact, it is contrary to the fact that is the essence of the proper understanding of this subject: the fact that acceleration at any instant is in proportion with actual power. To maximize acceleration, you must keep the engine speed as close to the power peak as possible, not the torque peak. It is certainly better to have seven speeds rather than four, but the reason is so that you can keep the engine speed close to the power peak. Stated more precisely and more correctly, it is so that at each instant, you can cause power to be as great as you can possibly make it. Only then will you have made acceleration as great as you can possibly make it. There are various ways by which it is easily possible to demonstrate the truth of this, but the way that is perhaps most meaningful to the audience here, is by way of the fact that wheel torque equates to power divided by wheel rotational speed, and by the fact that except for the loss to friction, power is the same at the engine as at the wheel. Power in is power out, the same as with an electrical transformer, ignoring the thermal losses in both cases. Given that wheel power is engine power, and given that wheel torque equates to wheel power divided by wheel rotational speed, it is apparent that whatever the value of wheel rotational speed happens to be at any instant, that wheel torque at that instant is in proportion with wheel power and thereby engine power. Thus, to maximize wheel torque at any given instant, it is necessary to maximize power, not engine torque per se.

As I recall, acceleration is equal to force divided by mass. That is why a vehicles horsepower to weight ratio is a good indicator of the acceleration potential. On a road racing course with many turns a vehicle with more torque will probably beat a car with more horsepower.

Now you are in effect equating "torque" with the performance of the engine at low rpm. As soon as you do that, you are operating in the realm of contrivances, and no longer in the substantive realm where the question is that how how actual torque and actual power are each analytically related to acceleration. There is a natural tendency to do what you did. It takes a determined will to keep from doing that. A determined will is required to fully embrace this truth: when the word "torque" is used in a fully substantive manner, there is no implication that low-rpm performance is more about torque than power, and no implication that torque has greater significance at low rpm than at high rpm. You may question the veracity or relevance of that statement, but even if so, the path that you are heading down is a stray path. It does not lead to the substantive, proper, orthodox understanding of how actual torque and actual power are analytically related to acceleration. The substantive, objective understanding of torque and power is concerned, intrinsically and expressly, with the manner in which actual power and actual torque are analytically related to acceleration, and the path you are heading down does not take you there.

In a perfect world with no friction a CVT equipped car that ran at it's torque peak continuously would out accelerate the same car that used a standard transmission.

Not to beat a dead horse, but again the property that you have ascribed to the torque peak is a property that rightfully belongs to the power peak.

That is why engine designers try to achieve as broad a torque band as possible. I'm not an argumentative sort but a pretty good automobile designer named Enzo Ferrari once said that "Horsepower sells cars while Torque wins races." He was hopefully making his statement on the assumption that both cars had plenty of both and also talking about Ferrari's forte.......road racing. I would not presume to argue with him.

Nor would I be inclined to argue with him, but for different reasons. I have no knowledge of whether Enzo actually said this, but if so, he was simply speaking in terms of contrivances, like most people do, using the word "torque" in a contrived, imprecise, non-substantive manner to refer to the performance of an engine over its full operating range, as distinct from its performance at its power peak. An awful lot of people do of course use the word "torque" in this manner, but this use of the word "torque" is not proper. And when statements are made where the word "torque" is used in this manner, those statements do not say or reveal anything about the substantive manner in which actual torque and actual power are analytically related to acceleration. It is the wrong path to go down, assuming that your goal is to arrive at the substantively correct understanding of the subject of torque and power.

And as for the torque band being as broad as possible, this raises all sorts of questions. If this is accomplished, is the power band also made as broad as possible? Do you measure in terms of absolute rpm, or do you measure in relative terms, taking the ratio of the upper limit to the idle speed? People very often speak of how broad the torque band is, and to a certain extent it is meaningful, but to the extent that it is meaningful, it is not apparent to me whether it is or is not equivalent to making the power band as broad as possible.

And where did the torque indicator (pound/feet) come from anyways. It's confusing since the term has two different accepted meanings for different properties, one is a unit of work (a scalar quantity) and the other is a moment of a force (a vector quantity). Silly....IMHO.

Yeah, anyone who has encountered this curiosity has no doubt pondered this. It makes you wonder if there is some hidden reality that physics has yet to discover. Work and torque are measured in identical dimensions (units of measure), and yet they are so different that, as you point out, one is scalar and the other vector. But I think that it is just one of those curious coincidences, that has no implications or consequences of any note.

Auto manufacturers rate an engine at peak torque which is also silly. There should be some way to rate the engine at average torque over a given powerband.

It is silly in my opinion to quote the peak engine torque. Peak engine torque in of itself means very little. If the associated rpm is included, then it becomes more meaningful because you can translate it to power (even if you prefer not to think of it that way), but even after translating it to power, you are talking about the amount power at one rpm for one engine, ostensibly compared to the amount of power at a completely different rpm for a different engine, and neither of those two different engine speeds have any particular, unique importance beyond the fact that it happens to be where the amount of work that the engine performs per each individual rpm, or per each individual intake stroke, is at its greatest. That just doesn't mean very much, because acceleration is linearly bound to the time rate at which the engine is performing work, not to the amount of work performed per each unit of rotation. The power peak in contrast is the peak value for the time rate at which the engine is capable of performing work.

Although a flywheel doesn't add torque or horsepower it can certainly affect the 60 foot time which will affect the trap speed. There are just too many variables to get angry at each other over what I see as basically semantics.

The flywheel simply increases the engine's moment of inertia, substantially increasing the moment of inertia of the crankshaft itself. It isn't all that different from just making the crankshaft more massive, except that by distributing the mass at greater radius, i.e., further from the center of rotation, you get more increase in the moment of inertia, for a given amount of mass. The moment of inertia scales with the square of the distance from the axis of rotation, or from the center of mass for a body floating freely in space. More specifically, you integrate over the volume, with the integrand being the product of infinitesimal point mass and the square of the radius. Manifestly, it is natural to do it using spherical or cylindrical coordinates. That's the sum total of what I remember about that. Well, not quite, but nearly so.

If necessary, we need to discuss this with cooler heads and we need to omit, whenever possible, all the silly symbols and statements.The full-throttle behavior of an engine can be approximately modeled as a device which has some function [FONT=MathJax_Math]τ[/FONT][FONT=MathJax_Main]([/FONT][FONT=MathJax_Math]ω[/FONT][FONT=MathJax_Main])[/FONT] associated with it. This fixes the torque it can produce as a function of engine speed (rpm). This function is not at all constant, although engineers often strive to make it as flat as possible.

I don't really want to flog that same old horse again, but the idea that engineers would strive to make the torque curve flat suggest the idea that acceleration is instantaneously maximized by way of maximizing torque, which isn't correct unless you are talking expressly about wheel torque, not engine torque. Optimal shift points occur such that the two engine speeds, immediately before and after the upshift, are equal-power points above and below the power peak. As such, it is apparent that engine torque necessarily undergoes an appreciable decrease before the optimal shift point is reached, at which point it is thereby possible for engine torque to increase abruptly and appreciably, as it must in order to compensate for the abrupt, appreciable drop in engine speed. It follows that shortly after you exceed the engine torque peak in 1st gear, you remain thereafter in the region where the torque curve has negative slope, i.e., decreases with increasing rpm. You do that for as long you continue to desire to maximize acceleration, and given that this is what you do, this draws the notion of the flat torque curve into question. Of course it remains true that you want engine torque at low rpm to be as great as possible, just as you do at every rpm. This is not different from saying that you want power to be as great as possible at low rpm as well as at every rpm. And given that what you really want is for torque (or power) to be as great as possible at every rpm, and given that you have to use that downward sloping portion of the torque curve lest acceleration decline in a stair step manner rather than smoothly and lest overall acceleration dramatically suffer if you were to try and keep the engine speed in the vicinity of the engine torque peak, the notion of the flat torque curve is suggestive of some sort of contrivance or misunderstanding.

Regardless, given the torque function, there is an associated power [FONT=MathJax_Math]P[/FONT][FONT=MathJax_Main]([/FONT][FONT=MathJax_Math]ω[/FONT][FONT=MathJax_Main])[/FONT][FONT=MathJax_Main]=[/FONT][FONT=MathJax_Math]ω[/FONT][FONT=MathJax_Math]τ[/FONT][FONT=MathJax_Main]([/FONT][FONT=MathJax_Math]ω[/FONT][FONT=MathJax_Main])[/FONT]. So if the torque is known at all speeds, the power is known at all speeds (and vice versa). You can't have one without the other. Remember, Modern transmissions have many closely-spaced ratios, so except at very low speeds (at the bottom of 1st gear), an engine may be kept close to its power peak for as long as desired. That means that a well-designed car that is driven well may produce a force [FONT=MathJax_Math]F[/FONT][FONT=MathJax_Main]∼[/FONT][FONT=MathJax_Math]P[/FONT][FONT=MathJax_Main]p[/FONT][FONT=MathJax_Main]e[/FONT][FONT=MathJax_Main]a[/FONT][FONT=MathJax_Main]k[/FONT][FONT=MathJax_Main]/[/FONT][FONT=MathJax_Math]v[/FONT]. This depends only on the peak power (and velocity), and explains why the power-to-weight ratio is such a good predictor of acceleration performance as I mentioned earlier.

To be honest I did not follow the analysis, but apparently your intent is to say that power should be maximized in order that wheel torque and acceleration both will be maximized. If this is the correct interpretation, your intent is correct. But to explain the significance of the power-to-weight ratio, it seems that it should be sufficient to point out that acceleration at any instant equates to actual power divided by the product of mass and velocity, and that as such, acceleration is maximized by way of maximizing power. Beyond that, I am curious as to why, if your intent is to now say this about the power peak, that up until this point you repeatedly made reference to the torque peak. Not to make such a fuss over that as to cause you to want to explain, which would serve no purpose that is at all worth pursuing, but it seemed appropriate to point this out. Please don't try to explain it. It isn't worth it.

Having said that, the torque peak is not completely irrelevant. Its position relative to the power peak is usually a good indicator of the size of the car's "powerband." Essentially, how high do you have to rev it in a given gear before the engine really gets going? Having a wide powerband is extremely important in everyday (or moderately aggressive) driving where you're not going to redline in every gear. It makes the car feel much more powerful even if the maximum performance is the same. God, I love Google and I am able to talk about this in normal language even though I graduated from MIT with a degree in Physics in 1973. I earned my Doctorate in 1980. Wanna Dance?:L

Indeed the torque peak is not completely irrelevant, but no data point could ever be completely irrelevant. It does in fact give a sense of the broadness of the power band, but only when the rpm where it occurs is also provided, and even then the sense it gives is crude. As for a sense of how peaky the power band is going to be, the location of the power peak itself gives a strong, useful indication of that, and does so even when the peak torque value is meaningless toward that purpose owing to it occurring very low in the rpm band. It would be enormously more useful if rather than quoting the peak torque value, the manufacturers would quote the power halfway between idle and the power peak. That single, simple datum, if provided, would be a far more consist, reliable, useful indicator of the comparative breadth of the power band than the torque peak could ever be. For the torque peak to be that useful as an indicator of the breadth of the power curve, it would have to always occur at rpm roughly at that midpoint, but it rarely does. Sometimes it occurs barely above idle, in which case the value will typically seem prodigious, and it often occurs above the midpoint of the range and often not so far below the power peak, in which case it typically seems meager.

Whenever I build an engine for a customer I strive to keep the torque band broad and I will not over cam an engine. I've lost some work because I won't do what the potential customer wants. The old saying that the customer is always right is always wrong. They have no idea and I'll not compromise an engine or it's driveability based on a whim from some one that doesn't know very much at all. I have many 500 FWHP engines that are daily drivers and some are over a hundred thousand miles. It can be done and done easily. Torque and horsepower are matched to gear ratios and if done properly they will drive great and even surpass some cars that have more horsepower. It's more complicated than just bolting some parts together. Of course, as always, that just IMHO.

I found your comments very interesting. I certainly hope that I have not said anything that you would find offensive or to which you would take any particular exception.

 

[TedC]

Rob,
Thanks for providing the link. That article explains why I like tree pulling engines like the L98. If I wanted to win 1/4 mile drag races or top speed honors, there are much better choices.