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Old 11-20-05, 10:21 PM   #1 (permalink)
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Hp vs. Torque

i figure this should go into the Lounge since the subject matter is amorphic (non make/model specifc)

i kinda look around and see that the two concepts are misunderstood by a great deal of car fanatics. on this forum as well as on the internet and outside of the internet.

what is torque:

Torque, as by its definition, is a twisting force. As by its unit of measurement, it's pretty dern straight forward. Nm (Newtons per meter), Kgm (Kilograms per Meter), Lbs.ft (Pounds per foot, or as we car people changed it to "Foot-Pounds") and any other mixture of unit measurement and unit force.

As this concept relates to automotives, the more torque you have the more massive your acceleration will be. This is a law, so there's no need to find a way out of it. Why? look at one of the fundamental equations the automotive is built upon....F=ma, Force is equal to Mass multiplied by acceleration. flipping this equation around you'll have acceleration is equal to Force divided mass or F/m=a. the higher the amount of force you have, the greater your acceleration will be. nothing more nothing less. that is given all things equal.

The only thing a driver feels when he "mashes" (as we say in the south) the accelerator is torque. there's no mysterious "horsepower" trunk monkey gremlin. it's all torque.

There's a saying that most people have heard, some haven't but it rings true if only people would listen. "Horsepower sells cars, Torque wins races" When you gather all things together this saying is more true than many people give credit to it.

with that said...you maybe thinking:

what is Horsepower:

Horsepower is something that people really dont understand too much. Without going into too much about kinetic physics and stuff, it's pretty much energy capable of being done in an amount of time, just like a Watt (or similarly a Joule with direction). Ever wonder why there's so many ways to calculate the rated power of an engine? you've got horsepower (hp) Pferdestarke (PS), Kilowatt(kW) and some others im missing. The one that should really make you question hp is kW.

What is a Kilowatt? well from the top, a Kilowatt is the amount of energy that can be produced over a certain amount of time with a direction, and this is equal to "work" or action taken on an object. If no motion is made, no work is done. i believe the time is 1 second. energy is a function of Force and distance in relation to time. To get more work done in a set time frame, you need to have more speed, or cover more ground. however you cover more ground is irrelevant at the current time. just know that to cover more ground in the same amount of time. you've had to expend more energy. in order to move 738 lbs 1 foot in one second, you basically need act 1 kilowatt of energy on that object.

now horsepower says that you have the ability to move five-hundred fifty pounds (550lbs) 1 foot, in one second.

Now putting it in terms of engines and power, imagine a crankshaft. you can see it spinning? take the stroke of our C32A engine at 84mm...multiply that by pi, then by rpm, divided by 1000, and then divide that by 60 and that will give you a number i dont know what to do with (j/k) but right now im just showing you what we did

soooo
84 x pi=264
264x (any rpm i'll do 1000)=264,000
divided by 1000=264
divided by 60=4

so...what we have here is four...four whats? 4 meters per second. how? 84mm is the stroke over a 180 angle, or the diameter. multiplying it by pi gives you the circumference, multiplying that by RPM gives you total distance traveled in 1 minute. dividing that number by 1000 turns that measurement from millimeters to meters, and then dividing that by 60 breaks that meters per minute into meters per second.

Now with this you can then say hmmm what if i double the rpm keeping the force the same. remember in this case we're dealing with rotational force i.e. torque. and since i've left torque/force out of this equation we'll call it a constant

blah blah bull crap up to rpm
264 (multiplied by 2000)=528,000
divided by 1000=528
divided by 60=9

Now, 9...9 meters per second if you cancel out the seconds from the watts, you've got distance covered is equal to 9 meters

9 meters covered is greater than 4 meters covered. therefore it's going to produce more energy, therefore more "work" is done.

energy in a direction over a set amount of time is equal to 1 watt. 745 watts equal 1 hp.

this is how engine dynos work. it gives a certain amount of resistance, the force needed to overcome that resistance is measured, if the force stays the same as the distance per second increases, the work done increases or...HP increases.

now when you look at graphs...



if you examine these, you'll find that as rpm, or distance covered in a set amount of time (think about the circumfrencial stroke of the crank shaft as a linear motion as opposed to eccentric or circular) get's greater. as does the work produced as well.

i tried to find the most linear graphs i could. linear torque curve i mean. With the first one it's pretty lumpy but it clearly shows how as the RPM goes up and the torque remains somewhat constant the work produced continues to go up.

in the second one you can see that the graph is still going up even up to its revlimit. that is...the HP is still climbing as well as the torque. But if you look closer, you'll see that HP is climbing at an exponential rate compared to torque. if the engine were to keep a constant torque (force) from 5000 through to 10,000 rpm the hp would be double that at 5000rpm, simply because the linear distance of the crankshaft doubled and inherently producing more work...



another one. this is a really good one. it's CLEARLY evident that the relationship of force to a distance over a set time is what is working here.

notice how the torque curve is flat, and the rpm just climbs and climbs...keeping the torque curve flat like that through 20,000rpm would produce. about 480hp. think on that now.....you'd say "FAWK! 480hp from a 2.0 4Cyl. naturally aspirated"....now then look at the torque....

125lbft of torque at 20,000rpm will give you 480hp. this is how F1 engines produce such ridiculous amounts of "WORK DONE" that can continue to accelerate long after a car of the same amount of power would have had to shift. there for more work is done and less time is wasted. I.E. turns into faster times.

application specific, the Type II versus Type I... The type II has less force over all, but can produce more work because the force it produces at the higher rpm range is greater than the force the Type I produces, therefore you end up with more work done. a side by side race between a Type II and Type I shows that it's the ability of the Type II to continue producing work after they accelerate from a stop that will make it (the Type II) pull away. the Type I has the Hole shot (because it has greater force behind it) but the type II produces more work as the distance traveled increases in order to catch up.

lets break a formula engine down to it's numbers...i believe it was a BMW engine that produced 950hp but that's all that was advertised. why? to make people think it was an amazing thing. what's really at work here is the power done. if we were to take it's numbers and find out the torque it produces at its rated peak HP rpm we'd stumble onto this...

at 19,000rpm (which is the advertised peak HP rpm) the BMW made 950hp...throw it through the math of 950x5252(a constant used in this calculation)/19000 we get

262.6lbft

do what? that's exactly right. 262lbft of torque...not much oomph is it? not compared to its hp, but in a light chassis like an F1 you get supremely fast acceleration because such a light chassis would accelerate like that with that amount of force.

now can see how an F1 really doesn't play on anything other than rpm. As a matter of fact....

since the car is light...you just played with the first equation too. F=ma...or F/m=a.

Reduce the M and you get more A with the same amount of F.

next time someone tells you This car has this much "horsepower"...ask about the torque.


food for thought. 100hp/liter is easily capable on almost any engine with just a good set of cams and light weight rotating assembly. however, how many cars can produce 100lbft/liter?...

im still trying to find one.

Stay up everybody, and thanks for giving me your time.

-Ivan

Last edited by B+O; 07-23-08 at 04:12 PM. Reason: Typos Fixed.
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Old 11-20-05, 10:31 PM   #2 (permalink)
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omg...mein brain...

edit: ok, my brain cooled down a bit, so i read a lil more, and its lookin interesting as hell...had to take another break tho...dont wanna get an internal BHG from overheatin

Last edited by Banana!; 11-20-05 at 10:42 PM.
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Old 11-20-05, 10:40 PM   #3 (permalink)
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Yup Sunday sure is the slowest day on here isn't it

Bang thats a great write up man...much respect for putting it up maybe a sticky in the Auto Discussion section is warranted??
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Old 11-20-05, 10:54 PM   #4 (permalink)
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Nicely put. Appreciated.
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Old 11-20-05, 11:12 PM   #5 (permalink)
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Very nice. Better put than the NATEF certified textbooks books.

Mods please sticky, excelent for noobies.
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Old 11-20-05, 11:23 PM   #6 (permalink)
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Wow man, that is awsome, thank you for posting...my brain started hurting a little bit about %90 of the post.
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Old 11-20-05, 11:54 PM   #7 (permalink)
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excellent post. thank you
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Old 11-21-05, 01:08 AM   #8 (permalink)
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why not just say torque is what pushed the cow down from a standstill, and hp is what runs into the cow knocking it down.
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Old 11-21-05, 10:15 PM   #9 (permalink)
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I was once told by a person i respect that has a 6.0l diesel(450hp with just da chip) the complete opposite of what i have always thougt and would like you guys to lend your thoughts...

"hp is what gets you off the line, torque is what gets you to the end..."--pretty sure that is an exact quote..remember he also has diesel.
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Old 11-21-05, 10:56 PM   #10 (permalink)
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Quote:
Originally Posted by swift
I was once told by a person i respect that has a 6.0l diesel(450hp with just da chip) the complete opposite of what i have always thougt and would like you guys to lend your thoughts...

"hp is what gets you off the line, torque is what gets you to the end..."--pretty sure that is an exact quote..remember he also has diesel.
he's half right.

in essence it's torque that gets you off the line and torque that keeps you going through the end. what HP is, is just a way to tell you how fast you can get the torque applied to the ground in the higher RPM range.

diesels don't play nice with high rpm, so they're torque monsters. Moreover they cant take that torque out to higher rpm-or a longer distance per unit time-as the get inefficient all you really end up with is slabs of torque, and a decent amount of hp (or the ability to use the force or torque it's capable of producing for longer and longer amounts of time.) if you peep a diesel run out, they usually fall off pretty hard after 3000rpm.



EDIT:



just found this. lets examine...

Lightblue=torque, darkblue=hp

oh where they cross is about 4000 rpm just for reference.

See how the light blue is huge on the bottom end? that's the torque. it's extremely stong on diesels. but since they aren't very efficient at keeping that torque as the distance covered per unit itme increases, it falls off...and HOW!

the dark blue is the HP. but if you can see, the light blue is falling off pretty steeply, the dark blue is kinda still going up for a minute but then falls off just as hard as the light blue? that's the torque falling off pretty hard, and since the torque is what you feel and HP is a function of that force over a said amoutn of distance per unit time, if you reduce the force per distance/unit time. you're going to have lower output. and that's what's happening in this dyno sheet. the force is falling off, as distance covered is getting greater, less force for the distance covered is equal to less work done, less work done is less ability to accelerate, and thus "less horsepower"

Last edited by B+O; 11-21-05 at 11:58 PM.
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Old 11-25-05, 06:44 PM   #11 (permalink)
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wow! thanks bang...great read, again.

See this is the info i can "retain"....
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Old 03-19-06, 09:55 PM   #12 (permalink)
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you said in your post that its lbs per foot, but if that was so, it would be lbs/foot, its not, its actually lbs^2foot/lbs which reduces to ft.lbs. its a measure of torque as kw is a measure of power. just so you know...
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Old 03-20-06, 12:16 PM   #13 (permalink)
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Quote:
Originally Posted by Ikeray
you said in your post that its lbs per foot, but if that was so, it would be lbs/foot, its not, its actually lbs^2foot/lbs which reduces to ft.lbs. its a measure of torque as kw is a measure of power. just so you know...
SAE is responsible for the Change in the name. in smaller units the units are ounce/inches, Newton/meters, Kilogram/meters, and so forth.

It would literally be pronounced Pounds/foot but how easily can you pronounce Pounds/foot versus foot/pounds? SAE officially called the units FootPounds. even though the correct name is Pounds/foot or lbs/ft

if you look ft.lbs is the inverse multiple of lbs/ft.
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Old 03-20-06, 02:18 PM   #14 (permalink)
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im refering to the fact that its not lbs divided by ft but lbs times ft, thats where ftlbs comes from. its something to do with the fact that something from metric gets squared when it comes over to american (std) measurement and when the cancellation is done it comes down to feet*pounds or footpounds.
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Old 03-20-06, 02:40 PM   #15 (permalink)
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its actually nothing to do with conversion at all.

a joule is equal to (mass*distance^2)/time^2[seconds].

hp = kg*g[gravity](9.8m/s^2)*distance/seconds

now doing simple conversion to american (std) and you get

hp=lbs*g*ft/sec
or in poundsforce hp=lbf*ft/sec where lbf=lbs*9.8 m/s^2(gravity)

now rather than going in a discussion about this, just read wikipedia's defination of torque in relation to hp (since i have gotten the units to measure hp for you)http://en.wikipedia.org/wiki/Torque

Last edited by IkeRay; 03-20-06 at 02:55 PM.
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