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OK, with all the torque of KW chasing, and rwkw figures everyone quotes in their siggs, I came accross this, and damn it's a good read..

It has some basic terminology to keep everyone understanding, and some calcs to keep the techs at bay..

So, what does this all mean...... well maybe it will make ppl better understand the physics of drag racing for one, and the importance of more than " how many KW u got"....

:bowdown:

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 :-). I've posted a subset of this note in another string, but felt it deserved to be dealt with as a separate topic. This is meant to be a primer on the subject, which may lead to serious discussion that fleshes out this and other subtopics that will inevitably need to be addressed.

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. 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 foot pounds 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.

Awhile 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 lift a 550 pound weight one foot in one second, thereby performing work at the rate of 550 foot pounds per second, or 33,000 foot pounds per minute, for an eight hour shift, more or less. He then published those observations, and stated that 33,000 foot pounds per minute of work was equivalent to the power of one horse, or, one horsepower.

Everybody else said OK. :-)

For purposes of this discussion, we need to measure units of force from rotating objects such as crankshafts, so we'll use terms which define a *twisting* force, such as foot pounds of 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.

Now, it's important to understand that nobody on the planet ever actually measures horsepower from a running engine. What we actually measure (on a dynomometer) is torque, expressed in foot pounds (in the U.S.), and then we *calculate* actual horsepower by converting the twisting force of torque into the work units of horsepower.

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, incidently, we have done 6.2832 foot pounds of work.

OK. Remember Watt? He said that 33,000 foot pounds of work per minute was equivalent to one horsepower. If we divide the 6.2832 foot pounds of work we've done per revolution of that weight into 33,000 foot pounds, we come up with the fact that one foot pound of torque at 5252 rpm is equal to 33,000 foot pounds 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 foot pounds 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 carland?

First of all, from a driver's perspective, torque, to use the vernacular, RULES :-). 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 foot pounds 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 isn't particularly meaningful from a driver's 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 pushback 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 the belt in the back? Now take it to the power peak, and punch it. Notice that the belt in the back is a bit weaker? Fine. Can we go on, now? :-)

The Case For Horsepower

OK. If torque is so all-fired important, why do we care about horsepower?

Because (to quote a friend), "It is 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 carland for a moment, and describe a waterwheel I got to watch awhile ago. This was a pretty massive wheel (built a couple of hundred years ago), rotating lazily on a shaft which 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(!) foot pounds 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 drivewheels of a car, that car would go from zero to twelve rpm in a flash, and the waterwheel would hardly notice :-).

On the other hand, twelve rpm of the drivewheels is around one mph for the average car, and, in order to go faster, we'd need to gear it up. To get to 60 mph would require gearing the wheel up enough so that it would be effectively making a little over 43 foot pounds of torque at the output, which is not only a relatively small amount, it's less than what the average car would need 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 HP.

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 Dragstrip

OK. Back to carland, 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 current LT1 Corvette 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

LT1 300 @ 5000 340 @ 3600

The cars are geared identically, and car weights are within a few pounds, so it's a good comparison.

First, 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 LT1 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 LT1 is faster. Here's another slice at that formula:

Horsepower * 5252

Torque = -----------------

RPM

If we plug some numbers in, we can see that the L98 is making 328 foot pounds of torque at its power peak (250 hp @ 4000), and we can 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 LT1 is fairly happy making 315 pound feet at 5000 rpm, and is happy right up to its mid 5s redline.

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 occuring a little earlier in the rev range, but that is debatable, since the LT1 has a wider, flatter curve (again pretty much by definition, looking at the figures). From somewhere in the mid range and up, however, the LT1 would begin to pull away. Where the L98 has to shift to second (and throw away torque multiplication for speed), the LT1 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 LT1, by definition, has an advantage.

Another example would be the LT1 against the ZR-1. Same deal, only in reverse. The ZR-1 actually pulls a little harder than the LT1, although its torque advantage is softened somewhat by its extra weight. The real advantage, however, is that the ZR-1 has another 1500 rpm in hand at the point where the LT1 has to shift.

There are numerous examples of this phenomenon. The Integra GS-R, for instance, is faster than the garden variety Integra, not because it pulls particularly harder (it doesn't), but because it pulls *longer*. It doesn't feel particularly faster, but it is.

A final example of this requires your imagination. Figure that we can tweak an LT1 engine so that it still makes peak torque of 340 foot pounds 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. OK, so we'd need to have virtually all the moving parts made out of unobtanium :-), and some sort of turbocharging 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 LT1 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'd 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 LT1 Vette in a quarter mile pass, and it predicts a 13.38 second ET, at 104.5 mph. That's pretty close (actually a tiny bit conservative) to what a stock LT1 can do at 100% air density at a high traction drag strip, being powershifted. 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, of course. It doesn't pull any harder, but it sure as hell pulls longer :-). It's also making *900* hp, at 15,000 rpm.

Of course, folks who are knowledgeable about drag racing are now openly snickering, because they've read the preceeding paragraph, and it occurs to them that any self respecting car that can get to 135 mph in a quarter mile will just naturally be doing this in less than ten seconds. Of course that's true, but I remind these same folks that any self-respecting engine that propels a Vette into the nines is also making a whole bunch more than 340 foot pounds of torque.

That does bring up another point, though. Essentially, a more "real" Corvette running 135 mph in a quarter mile (maybe a mega big block) might be making 700-800 foot pounds of torque, and thus it would pull a whole bunch harder than my paper tiger would. It would need slicks and other modifications in order to turn that torque into forward motion, but it would also get from here to way over there a bunch quicker.

On the other hand, as long as we're making quarter mile passes with fantasy engines, if we put a 10.35:1 final-drive gear (3.45 is stock) in our fantasy LT1, with slicks and other chassis mods, we'd be in the nines just as easily as the big block would, and thus save face :-). The mechanical advantage of such a nonsensical rear gear would allow our combination to pull just as hard as the big block, plus we'd get to do all that gear banging and such that real racers do, and finish in fourth gear, as God intends. :-)

The only modification to the preceeding paragraph would be the polar moments of inertia (flywheel effect) argument brought about by such a stiff rear gear, and that argument is outside of the scope of this already massive document. Another time, maybe, if you can stand it :-).

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 thus have more effective torque *at the drive wheels*.

Finally, operating at the power peak means you are doing 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 if you factor in gearing vs car speed, the power peak is *it*. An example, yet again, of the LT1 Vette will illustrate this. If you take it up to its torque peak (3600 rpm) in a gear, it will generate some level of torque (340 foot pounds times whatever overall gearing) at the drive wheels, which is the best it will do in that gear (meaning, that's where it is pulling hardest in that gear).

However, if you re-gear the car so it is operating at the power peak (5000 rpm) *at the same car speed*, it will deliver more torque to the drive wheels, because you'll need to gear it up by nearly 39% (5000/3600), while engine torque has only dropped by a little over 7% (315/340). You'll net a 29% gain in drive wheel torque at the power peak vs the torque peak, at a given car speed.

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, theoretical "best" top speed will always occur when a given vehicle is operating at its power peak.

"Modernizing" The 18th Century

OK. For the final-final point (Really. I Promise.), what if we ditched that water wheel, and bolted an LT1 in its place? Now, no LT1 is going to be making over 2600 foot pounds of torque (except possibly for a single, glorious instant, running on nitromethane), but, assuming we needed 12 rpm for an input to the mill, we could run the LT1 at 5000 rpm (where it's making 315 foot pounds of torque), and gear it down to a 12 rpm output. Result? We'd have over *131,000* foot pounds of torque to play with. We could probably twist the whole flour mill around the input shaft, if we needed to :-).

The Only Thing You Really Need to Know

Repeat after me. "It is better to make torque at high rpm than at low rpm, because you can take advantage of *gearing*." :-)

Edited by seventytwo
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very good, have also seen a write up by an american guy on a rotary website, comparing theiretically identical cars, one with an oldish (early 90's maybe) honda V10 F1 engine, and the other with a dodge ram V10 diesel, both same weight, and geared correctly for max speed of 300kph.

in the theoretical model, the diesel made a heap more torque, but once the gearing was changed to give the same speed at max RPM/power (cant remember which) the F1 powered vehicle was faster.

the power til 10,000+RPM (with appropriate modifications) is one of the reasons I like to play with rotaries :)

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It contains such things as:

Now, it's important to understand that nobody on the planet ever actually measures horsepower from a running engine.

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It contains such things as:

Now, it's important to understand that nobody on the planet ever actually measures horsepower from a running engine.

Well there you go...It does too! :ibrungatorch:

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And

Therefore, horsepower isn't particularly meaningful from a driver's perspective, and the two numbers( HP & Torque ) only get friendly at 5252 rpm, where horsepower and torque always come out the same.

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It contains such things as:

Now, it's important to understand that nobody on the planet ever actually measures horsepower from a running engine.

<{POST_SNAPBACK}>

that's becasue your likely to lose a finger if you tried. :crybaby:

Dazza.

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The Only Thing You Really Need to Know

Repeat after me. "It is better to make torque at high rpm than at low rpm, because you can take advantage of *gearing*." :-)

I'm still a little confused .... the XR6T makes max torque of 450nm from a low 2000rpm to 4250rpm. Ford make a big fuss that the T makes so much torque from down low, but wouldn't the T be better if max torque was produced at a higher rpm ???? Why is it such a good thing that the T makes the torque down low ???

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The Only Thing You Really Need to Know

Repeat after me. "It is better to make torque at high rpm than at low rpm, because you can take advantage of *gearing*." :-)

I'm still a little confused .... the XR6T makes max torque of 450nm from a low 2000rpm to 4250rpm. Ford make a big fuss that the T makes so much torque from down low, but wouldn't the T be better if max torque was produced at a higher rpm ???? Why is it such a good thing that the T makes the torque down low ???

<{POST_SNAPBACK}>

Because the conception of a turbo car is that you have to rev the beegeesus out of it to mak it go, and they have no torque. They are appealing the V8 brigade, who's main argument is the Torque factor, or lack of it.

Generally though, that applies to 4 cylinder's where they don't make torque like v8's, but then, the're half the size so how could they??

Also helps with the 'pulling power' aruguement, where with towing, one needs low down urge..

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The Only Thing You Really Need to Know

Repeat after me. "It is better to make torque at high rpm than at low rpm, because you can take advantage of *gearing*." :-)

I'm still a little confused .... the XR6T makes max torque of 450nm from a low 2000rpm to 4250rpm. Ford make a big fuss that the T makes so much torque from down low, but wouldn't the T be better if max torque was produced at a higher rpm ???? Why is it such a good thing that the T makes the torque down low ???

<{POST_SNAPBACK}>

But it also says, or at least strongly infers, that a flat long lasting torque curve is even more desireable. And this is exactly what you get with a big turbo engine.

The quote "It is better to make torque at high rpm than at low rpm, because you can take advantage of *gearing*." should be read as pertaining to naturally aspirated engines where the design may be altered to achieve either one characteristic or the other but not both. That is to say, atorquey low revving engine will feel quicker off the line and during rolling accelleration as in everyday driving BUT a somewhat less torquey but higher revving and better breathing engine will perform better at constant full throttle driving as in competition use.

A forced induction engine gives you the best of both worlds ... :spoton:

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  • 4 years later...

Brilliant write up!!! ive been doing a little study on this myself, when you say its best to make torque higher in the rev range rather lower to make use of gearing I believe that to be true for sport applications but for everyday driving I would seem it would be better to make peak torque lower in the rev range so that the engine doesn't need to work as hard for everyday stop start traffic acceleration.

Just to extend from your previous post

Take for example a humble v6 commodore (I know but I was a big Expensive Daewoo man) Peak torque occurs at 3600 rpm and develops a respectable 304 nm. This engine can easily pull away in traffic to overtake without needing to drop back 2 or 3 gears to meet its peak torque requirement. Its final drive is also at 3.08:1. Yet saying that the car isnt terribly fast by any means due to its rather low peak power of 147kw @ 5200.

Say if you wanted to increase performance of this car? you really have two options (as with any car) you can keep peak torque the same at 3600 and increase engine speed or increase peak torque at 3600 rpm or ideally at a higher rpm as F6 Ute stated.

Mods like your extractors will increase efficiency of the engine and will indecently raise your peak torque at a higher RPM (if that is your extractor design) thus making your mid range acceleration feel faster as the engine can breath better at the higher RPM thus more torque so maybe instead of the original 304nm @ 3600 it maybe be 304nm @ 3700rpm or 3800rpm.

For our turbo cars the beaut thing about turbos is that they by definition increase efficiency compared to a n/a car due to the engine inhaling a greater volume of air at lower rpm compared to the n/a car.

Example an engine of 4 liters will suck in "roughly" 4 liters of air every crankshaft revolution and that amount is fixed the trick is to increase how efficiently the engine does it at any given RPM (usually the cam profile (lift,duration & overlap) will determine this). Turbocharges and supercharges as you all should know work by forcing air into the engine and increasing the volume inside the cylinders and like you all know more air means more fuel and the result of that is more "torque" at any given rpm.

Now when it comes to the xr6 turbo motors quoting a peak torque figure of 480nm at 2000rpm onwards to around 4500rpm I believe that that means that the turbo can feed the engine significant amount of air (therefore fuel) to create 480nm from as low as 200rpm to 4500rpm and hence the very large power output of 245kw at at low 5250 rpm.

Now imagine the likes of a n/a car like my 3.8l Late model camira earlier how fast would the motor have to spin to create that power output or how aggressive would the cam specs have to be to get that power? The cam would have to be designed to be most efficient at a very high rev range making for a fairly unpleasant daily driver as the engine would be choking at low rpm.

I think at the end of the day car manufacturers endeavor to build engines which deliver a broad torque curve across the rev range which allows low speed acceleration with high speed power.

Hope that maybe shed some more light on the topic and hopefully reinforces what F6 Ute was saying earlier.

Edited by Benji_vs
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  • 5 weeks later...
Awhile 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 lift a 550 pound weight one foot in one second, thereby performing work at the rate of 550 foot pounds per second, or 33,000 foot pounds per minute, for an eight hour shift, more or less. He then published those observations, and stated that 33,000 foot pounds per minute of work was equivalent to the power of one horse, or, one horsepower.

its an interesting fact that James Watt actually undercut the power of a horse to help him sell steam engines. when he presented potential customers (like large mines, etc) the figures showed the engine to be more appealing than the teams of horses it would replace

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Great read... my wife asked me to explain the difference between torque and kw as I finished reading this... I laughed at her and made her read it. She took it all in, better than me I think.

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  • 8 months later...

The Only Thing You Really Need to Know

Repeat after me. "It is better to make torque at high rpm than at low rpm, because you can take advantage of *gearing*." :-)

That is an extremely comprehensive right up F6, I admire what you are trying to do do for everyone.. :shocked:

However I believe I can add something to your motto that may make it a little more understanding; here I go short version lol;

Ok lets elaborate on taking advantage of gearing & torque at higher rpm (Drag Related) if your engine spins to 6500rpm and your tune and timing is designed to give you peak torque lets say 800nm at 2200rpm and let us also assume that your tune at 4500rpm makes 650nm and at 5500rpm makes 550nm finally getting to 6500rpm and making 450nm.

When your peak is at 2200rpm and lets say you launch your car with an auto and stall @ 2800rpm this may end up being a good thing and with the right tires launching off-peak may give you a better 60ft right? after first gear has come and gone and you shift to second @ what rpm will you engage second gear? Lets say 4000 to 4750rpm right? So what you are doing is running the rest of the race with between 650nm and 450nm of power (totally OFF-peak)!!!!! Remember when you are racing most of the gears are only using between 3500rpm and 2500rpm depending on your transmission and engines rev-range... So how good is a tune that makes all the torque very early for the drag strip people??????

The key/target for a drag tune is to match your maximum torque with your usable rpm range between shifts depending on transmission/gearing!! Remember this! it all you need to know in this department (Drag Racing)

Hope this helps!!

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Makes sense, after the first gear is gone you certainly aren't back in 2000RPM range until the race is over.

Just strip the car out to get moving quicker in 1st hahaha :)

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  • 4 weeks later...
  • 1 year later...

aweseome read, I was doing some research on this the other day.. also bored.. and gave up because there was too much random stuff on the internet, and couldnt find anything clear, looked again tonight and sure enough saw a link into xr6turbo forum, very nice write up mate I understand now!

cheers :drinks:

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  • 3 years later...

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