Torque Explained

[neoviper]

This thread is calling for the attention of all Moderators, Wiseman, and any other knowledgeable members on this site.

The first thing you usually hear any newb say is " How can I make more power? ", " How much HP will I gain from xxx?", and plenty other questions related to HP. Most people (not all) draw all the attention to HP in dyno runs and don't pay much attention to the second number on that slip.

I for one am interestred in learning more about tourqe, how it's measure, how it's produced, proven methods as well as theories on increasing it.

This forum doesn't really have any threads that get into this, or explain it too well. I am hoping that this thread and all the input that goes into it will educate others such as myself in better understanding torque.

Have at it boys!

 

[dsmdragon]

Well, if at first I will tell you what the both mean to one another.
If you have HP but no torgue then you'll not get anywhere quick, but are able to drive at a higher speed but never be able to get to that top speed. -
If you have torgue but little HP, then you'll get there faster but not be able to reach a higher speed. One way to get more torgue is different size tranny gears (most all out drag cars use 3) So get HP but almost most the time take out torgue. Or take torgue and loss top speed-by some, but kill people with your acceleration.

So that said, you should understand what the two do for you and for one another.
You get torgue from the power you produce off the crank, and sends it through the trany,gears,and driveshafts/axles to the wheels, But through these parts you loss some torgue or acceleration force. This is why you have your sticky tires and light weight parts like: pulleys and flywheels to free you the torgue force lost by weight reduction and contact the path to the ground.

That should help you understand a little

 

[neoviper]

Also it should be noted that HP is derived from torque.
Tourque x RPM/5252= HP. I believe this is the formula for calculating HP from torque

 

[turboglenn]

Torque is the power hat gets you moving, horse power is what keeps you pulling in the top. They always cross at 5250 RPMs for some reason. As for actuall definitions, you might just google it. I think it has something to do with torque being work that is done and horse power is how much it takes to move a certain amount of weight vertically in a certain amount of time.

I like toquey motors ( turbo cars usually aren't becasue of low compression ratios to make room for boost) Torque is what pulls tree stumps out the ground and gets you that great 60 foot time. HP is what makes you pull had onthe top end of the track.

These explanations are totally just simple examples, I've read this stuff my whole life and still ahve to go to the books to get the true definitions when i need em

Do some googling and you'll probbaly find what you're looking for if no one here has what your trying to hear.

 

[neoviper]

I'm looking for this to be a general discussion about the topic. I've done research on this and have some knowledge of it. But there is so much more I want to learn about it. I figured doing it this way would help alot of other members as well.

 

[dirty32]

I just finished a college physics course which was all about torque. Here is the reader's digest version.

Torque is simply the force applied at the surface of the dyno (in lbs) multiplied by the radius of the drum of the dyno which your cars wheels are on (in ft). The multiplication of the two pieces of data results in the torque produced in the units ft-lbs. The lbs of force are calculated from the change in interia of the drum of the dyno. There are also brake dynos which use a brake to measure the torque.

I have read a few very good write ups in magazines which cover the basics of how a dyno works and what exactly torque and horsepower are.

Horsepower is a value calculated from torque and RPMs as stated above which the equation. If you notice on dyno plots the lines for torque and horsepower will always cross at the 5252 RPM mark which is because of the equation.

I hope that this helps out.

 

[tkelly27]

Torque - Wikipedia, the free encyclopedia

"In physics, a torque (&#964 is a vector that measures the tendency of a force to rotate an object about some axis [1]. The magnitude of a torque is defined as force times its lever arm [2]. Just as a force is a push or a pull, a torque can be thought of as a twist."

It's a force at a distance away, exactly like your torque wrench. The axis of rotation can be about the crank, or at the end of the wheels, or anywhere else you'd feel like measuring it.

Power (physics) - Wikipedia, the free encyclopedia

In physics, power (symbol: P) is the rate at which work is performed or energy is transmitted, or the amount of energy required or expended for a given unit of time. As a rate of change of work done or the energy of a subsystem.

Torque is force at a distance. The reason you can convert them is in the "units" section of the wikipeda section on torque.

"The joule, which is the SI unit for energy or work, is also defined as 1 N m, but this unit is not used for torque. Since energy can be thought of as the result of "force times distance", energy is always a scalar whereas torque is "force cross distance" and so is a (pseudo) vector-valued quantity. Of course, the dimensional equivalence of these units is not simply a coincidence; a torque of 1 N m applied through a full revolution will require an energy of exactly 2π joules."

The 5252 comes from unit conversions. I probably skipped that class, because I'm not getting them to work out.

Torque is most often measured because it is easier to measure. For example in an inertial dyno,
"Torque = rotational Inertia (I) times angular acceleration (&#945. This equation shows that, if an object has an angular acceleration, there is a torque on it." You can easily measure the angular acceleration, the rotational inertia is known (rotational inertia is basically mass), and from that you know your torque. Other dyno devices use a water brake to measure torque, which is more complicated and something I understand less.

Torque is produced by the downward force of the piston acting on the crank shaft.

There are two ways to produce more power. Increase the torque (increase the pressure in the cylinder on combustion which increases the force put on the crankshaft) or increase the RPM. Motorcycle engines produce very little torque, but produce a lot of power because they spin so fast. The problem with both of those is that they break parts, and with higher RPM operation, the time for the gasses to enter and exit the engine become a problem.

The reason people focus on the HP number is that to accelerate to a given speed in a certain amount of time requires a given amount of power. There was a quote in a magazine by some old racer that said "if torque won races, everyone would shift at 3000rpm"

That being the case in all of that, I really don't have any technical idea of what more torque will do for you... Can't wrap my mind around it I guess

 

[neoviper]

Awesome info! That does a good job of explaining how torque is calculated and where we get the numbers from

Torque - Wikipedia, the free encyclopedia


It's produced by the downward force of the piston acting on the crank shaft.

.

So this is why stroker motors produce more torque?

Torque - Wikipedia, the free encyclopedia

There are two ways to produce more power. Increase the torque (increase the pressure in the cylinder on combustion which increases the force put on the crankshaft) or increase the RPM. Motorcycle engines produce very little torque, but produce a lot of power because they spin so fast. The problem with both of those is that they break parts, and with higher RPM operation, the time for the gasses to enter and exit the engine become a problem.

So generaly speaking a higher revving engine will produce less torque but more power than a normal revving engine?

Torque - Wikipedia, the free encyclopedia

The reason people focus on the HP number is that to accelerate to a given speed in a certain amount of time requires a given amount of power. There was a quote in a magazine by some old racer that said "if torque won races, everyone would shift at 3000rpm"

This being said, is this talking about drag racing or track racing, seeing as good low to mid range torque is essential for accelerating out of corners?

 

[tkelly27]

Edit your post, don't make 3 new ones please.

1st one, from what I've read, yes. The extra displacement adds to this by allowing more gasses in for combustion. I'm not sure the dynamics of this, but if you put the same force on a longer arm, you will get more torque.

2nd one, No. If you take a stock 2.0 and rev it to 10k, you'll have the same curve as if you rev'd it to 7.5k. However, many of the modifications you do to get it to operate at 10k, shift the torque curve up to produce more torque higher in the rev range. Bigger cams, tuned intakes, exhausts, and (I think) bigger volume cylinder heads push the torque curve higher up in the rev range. The car will feel less torque, but it's just that the torque peak is not where you're accustomed to it being.

Check these out, essentially the same engine, just a different cam and an 80hp difference
XE250H-10, Camshaft Part#12-230-2 Dyno Sheet
XE294H-10, Camshaft Part#12-254-3 Dyno Sheet
I don't know why the torque peak is less, but it's not as huge of a difference as the power peak. The torque peak has been shifted over 400rpm. Look where the power peak occurs as well, 1100RPM difference.

3rd one, yes and no. I think this is a misnomer. You don't see F1 or NASCAR, or even rally car engines being built for maximum torque (you don't need to rev an engine to 20,000rpm to get maximum torque). You'll see their gear boxes being built to put them in their power band at any given point on the track. If you are limited in your ability to do this, then you want your power band as flat and wide as possible so that you are always in it, not generally a feature of high RPM engines. That's the way I understand it at least.

AHA!
Horsepower vs torque

 

[dsmdragon]

It is true that the more piston travel the more acceleration/torque you get. But if you are talking about track running then you need both numbers close to one another but with the numbers higher, it wont mean anything if you don't have good traction-So as to apply it to the ground...

 

[rrussell]

This is where the constant 5252 comes from.


The word horsepower was introduced by James Watt, the inventor of the steam engine in about 1775. Watt learned that "a strong horse could lift 150 pounds a height of 220 feet in 1 minute." One horsepower is also commonly expressed as 550 pounds one foot in one second or 33,000 pounds one foot in one minute. These are just different ways of saying the same thing. Notice these definitions includes force (pounds), distance (feet), and time, (minute, second). A horse could hold weight in a static position but this would not be considered horsepower, it would be similar to what we call torque. Adding time and distance to a static force (or to torque) results in horsepower. RPM, revolutions (distance) per minute (time), is today's equivalent of time and distance.

Now if we are measuring torque and RPM how can we calculate horsepower? Where does the equation HP=TORQUE * RPM / 5252 come from? We will use Watts observation of one horsepower as 150 pounds, 220 feet in one minute. First we need express 150 pounds of force as foot pounds torque.

Pretend the force of 150 pounds is "applied" tangentially to a one foot radius circle. This would be 150 foot pounds torque.

Next we need to express 220 feet in one minute as RPM.

The circumference of a one foot radius circle is 6.283186 feet. ft. (Pi x diameter 3.141593 * 2 feet)

The distance of 220 feet, divided by 6.283185 feet, gives us a RPM of 35.014.
We are then talking about 150 pounds of force (150 foot pounds torque), 35 RPM, and one horsepower.
Constant (X) = 150 ft.lbs. * 35.014 RPM / 1hp
35.014 * 150 / 1 = 5252.1
5252 is the constant.
So then hp = torque * RPM / 5252

 

[neoviper]

Great find on the link tkelly! This is the type of information I was hoping this thread would produce. It was also really intersting to read up on the formula for calculating shift points. Im gonna experiment with this.
Keep the input coming guys, this would make a good tech article!

 

[rrussell]

So this is why stroker motors produce more torque?

Stroker engines produce more torque based on more displacement of the engine.

Example:
Stock 4G63 engine 2.0L
5000rpm
sea level
20psi at the intake
IAT 80*F
12.0 A/F ratio
BSFC.5
VE 100%
air lbs/min.=30.56
305HP
321 ft/lbs torque

Now a 2.1L stroker engine with the same rpm,elevation,psi,IAT,A/F ratio,BSFC,VE
air lbs/min=32.06
320HP
336 ft/lbs torque

Now of course this is a example based on both engines at the same VE.

 

[tkelly27]

/ \ he's probably right. There are a lot of dynamics that go into it though.

Torque and Power

myth #5. Seems to be the case, but it doesn't quite settle with me. I guess you'd have to compare peak torque outputs from two engines of equal displacement and airflow characteristics.

 

[slowgsr]

Anyone know why our engines cross HP and TQ at 5252??? I will post the answer up tommorow if no one gets it!!

 

[rrussell]

Anyone know why our engines cross HP and TQ at 5252??? I will post the answer up tommorow if no one gets it!!

Because 5252 is the constant in the equation. Therefor HP and torque will be the same at 5252rpm.

 

[TunaTalon]

Torque is produced by the conversion of pressure on top of the piston to twisting force on the crankshaft. More displacement, more boost, power adders, or higher compression ratio will produce more pressure on top of the piston.

Conversion of pressure to torque is a function of Stroke and rod ratio. More stroke and lower rod ratios will produce more torque.

Note that there is no element of time in the measurement of torque.
Horsepower is a function of work over time so it can be calculated from torque and RPM.

Also note that longer strokes and lower rod ratios limit the maximum RPM of an engine and so limit the maximum horsepower. This is the classic design trade off between more top end power and more low end torque.

For the details on the math and examples of different versions of 4G6X engines please see my StrokeOrNot document at http://www.kidzuku.com/StrokeOrNot.pdf.

 

[rrussell]

TunaTalon thanks for the killer write up!!!

I will use alot of the information on my new engine build major Kudos

 

[probegonedsm]

torque is the amount of force placed on a rotating object, the more torque you have, the more force you can put to that rotating object. torque is useless without horsepower, vise versa, torque is made by your internal componets, where as horsepower is made by what your engine is taking in, air, gas, ect, mixing in the combustion chamber, exploding with the spark plug, and blowin out the exhaust, if you want more hp, flow more air, more gas, and ope the exhaust up. more torque, bigger cams, bigger piston, stroke it out. and yes, its ideal to have the hp and the tq close together, is makes for a nice launch, and a great run. i know this is genaral knowledge, but thats my 2 cents.

 

[CTP]

Wow... this thread is filled with a disgusting amount of misinformation.

"Torque is what gets your car moving and HP is what keeps it going." Are you kidding me? What are you a car salesman.

You need to understand that HP and torque are two different ways to measure the same thing. It's like a gallon of water vs. a pound of water. Trying to compare them as if they're the same type of measure is ridiculous. Either one can be taken separately on a dyno chart and tell you just as much if you understand how they work. Dyno charts have both because looking at a torque curve is the easy way to see instant engine force output that isn't effected by RPM, this is very useful for tuning. In fact, a torque curve is really the only thing you need to be looking at while tuning. The HP curve is just a simplified way to see how that torque is actually going to be delivered (hence, how it is effected by RPM). If you want to know how fast your car is going to accelerate, all you really need to look at the HP curve.

Here, just read this. After having an endless number of these HP vs. Torque debates, this article was finally posted and it's the most thorough and easy to understand explanation that will forever end the misinformation and misconcenptions. Ironically enough, it's written by a Harley guy. Who knew they had any brains?

Torque vs. Horsepower

 

[slowgsr]

Horsepower is a number calculated from Torque and RPM, thats it. Torque is a twisting force, horsepower can also be caclulated on electric motors by dividing power out (power left after all copper losses are accounted for) by 746 will give you the HP of that electric motor, before any mechanical losses, hysterisis, eddy currents, etc etc.. Without measuring torque at all.

Anyone know why Horsepower and Torque cross at 5252? I can tell you it has something to do with the VE of an engine.

I could explain a hell of alot more about DC electric motors! Gasoline Engines on the other hand.. Ive only read a few books, never had any teaching about them.

 

[CTP]

Speaking of misinformation....

Horsepower is a number calculated from Torque and RPM, thats it.

Wrong. It's a measure of work. In the case of a car it's a measure of acceleration.

Anyone know why Horsepower and Torque cross at 5252? I can tell you it has something to do with the VE of an engine.

Wrong. It's because of the math that relates the two measures.

 

[bastarddsm]

Torque is the measure of the amount of rotational force, that a body can exert. power is a measure of the distance the force moves a body per unit time. horsepower is a unit of power it is the ablity to do 550 ft lbs of work in 1 second. The reason that the hp and tq curves cross at 5252 is that horsepower is derived from torque. If we were to measure our power in Watts or PS, then they would cross at a different rpm.

 

[TunaTalon]

There is no profit in arguing math.
"HORSEPOWER: In its purest definition is: 1 HP= 33,000 Foot-Pounds of WORK Per Minute. In measurement, it is TORQUE multiplied by RPM divided by 5252."

Please see JIM MILLER for more details and the literal definition of torque.

I could try to simplify horsepower and torque for just the DSM community but there is already an open thread for misleading statements.

 

[Mr Peepers]

Peak torque in the rpm band is the most acceleration in a given gear.

The torque curve is the exact acceleration you "feel."

Peak HP in the rpm band is the most acceleration at a given speed.

Meaning, if you're going 60 mph, you'll want to be in the gear which lands closest to the peak hp for maximum acceleration.

A car with unlimited gear ratios(cvt) CAN NOT accelerate any faster than maintaining the rpm where it creates peak HP.

Torque is a rotating force at the crank, and HP (through gearing) is torque at the WHEELS, which is exactly the same as real-life acceleration.

Torque is a measure of force (twisting force), and HP is that at an rpm. HP is derived from torque, from the equation HP=TQ*RPM/5252. By looking at this equation, you can see that when the rpm is 5252, it is cancelled out by the constant factor, 5252, making the equation HP=TQ*1 or HP=TQ further simplified. This is why HP and TQ are the same at 5252 EVERY time NO matter what. People get confused when the graphs have a different scale for HP or TQ, but put it back to 1:1 and it will indeed cross. HP is only an equation, derived from TQ and RPM.

A "simple" way to increase HP is to shift the torque curve higher up in the rpm band. You can also think of this as being able to use "leverage through gearing." Otherwise, without changing rpm where the torque curve lands, you CAN not increase Hp without increasing torque. You can, in theory, get whatever HP you want by increasing the rpm an engine gets a certain torque value at.

There is A LOT more to be said about it, and Horsepower vs torque can explain it better than I can.

Once you wrap your mind around it, you can relate it to real world experience and not just numbers. It's a simple equation, thats all HP is, but being able to apply it is something people have trouble with.

BTW, nice link TunaTalon. Although it looks to me that people have a hard time understanding how the definition/equation translates into the real world.

EDIT: tkelly27 beat me to the link I posted... It's worth reading twice

EDITx2 : Another one, I may have explained it better: http://www.dsmtuners.com/forums/bolt-tech/265396-question-about-hp-tq.html#8 and SEiGHT - Torque vs. Horespower is another great link for understanding the correlation.