toruqe versus acceleration

before i get flamed and told to read the numerous faqs, id just like to say i think i uderstand the difference and want to know if i am correct. torque is actual acceleration, while horsepower is the cars ability to hold that acceleration across an rpm range. is this right?

more like, torque is the available power and horsepower is the duration that power can be held.


i might be wrong... i'm on some pretty cool pain meds for my oral surgery yesterday...

Torque is holding ability, horsepower is acceleration. although this depends on your gearing, or basically what your putting to the ground is all that matters...but its better when it looks smooth :)

Horsepower dictates how much torque is applied per minute

so 300 ft/lbs*6000 RPM is 1,800,000 ft/lbs of torque per minute at 6000 RPM.

Meh.

before i get flamed and told to read the numerous faqs, id just like to say i think i uderstand the difference and want to know if i am correct. torque is actual acceleration, while horsepower is the cars ability to hold that acceleration across an rpm range. is this right?

Kind of, when loosely defined. :smile:

Actually Torque and HP are the same. HP is simply Torque when applied across time. HP = Torque x RPM / 5252.

In Physics terms.. Torque is Force, and HP is Work. You can apply lots of Torque, but if nothing moves no real work is done. Given a fixed Torque (Force), the faster it moves, the more work is done.

Using the above formula, you can see that if an engine produces 300 lbs of torque at 5000 RPM, it will produce 285HP at that RPM.

The same Torque at 4500 RPM is only 257HP.

Got all that? Now, again by observing the above formula you can see that all recipricating engines at 5252 RPM develop the same Torque and HP.

You can also see that the ONLY way to increase HP is to either increase Torque, and/or increase the RPM point that that Torque is developed at.

Jim
SR Racing

before i get flamed and told to read the numerous faqs, id just like to say i think i uderstand the difference and want to know if i am correct. torque is actual acceleration, while horsepower is the cars ability to hold that acceleration across an rpm range. is this right?

Torque is proportional to the actual acceleration at any given rpm. However, power represents the potential acceleration for any given road speed.

With a fixed gear (i.e a 5 speed) transmission the maximum torque occurs at a lower road speed with respect to maximum power. This is why peak acceleration always occurs at peak torque. However, if peak power occurred at the same road speed as the peak torque, acceleration from peak power will always be higher.

By definition torque resents the work performed by the engine at any given rpm. Power (horsepower is just the units of power in the imperial system) is the rate of work for some period of time. The period of time varies with RPM, higher engine speed implies a shorter period of time. So power is a measure of work [per unit time] that has been adjusted for engine speed.

In Physics terms.. Torque is Force, and HP is Work. You can apply lots of Torque, but if nothing moves no real work is done. Given a fixed Torque (Force), the faster it moves, the more work is done.

Actually, torque is representative of work and power (horsepower is just a unit) is representative of power. Torque is measured by force (pounds (lbf) or newtons (N)) multiplied by distance (feet (ft) or meters (m)). Thus, the resulting units of torque are usually lb-ft or N-m depending on the dimensional system.

Torque can be applied to a shaft and the shaft does not need to rotate for work to be done. By definition torque is always a force applied at some distance. Power, is work for a given period of time. In order, for power to be applicable a time component is required. With regards to an engine the time component is derived from shaft speed. If a torque is applied to a shaft and the shaft does not rotate power equals zero. Since time is proportional to shaft speed, and a shaft speed of zero implies infinite time.

Both need to work together :)
Balance the performance

Torque can be applied to a shaft and the shaft does not need to rotate for work to be done..

Sorry. No work is done. (Other than the creation of heat) No meaningfull measureable work is done.

Work, BY definition requires motion. (at least when discussing an engine), uless your intent is to just develop heat. Obviously by the laws of thermodynamics, the energy is there in some form, but when discussing an engine the work we are interested in is movement.

Jim
SR Racing

Actually, torque is representative of work and power (horsepower is just a unit) is representative of power.

The inverse is true
??? "Torque" is a unit of rotational "force." It has nothing to do with "power" or "work".

Yes, Horsepower is just a unit, but it is representative of force and time. (or RPM).

As posted, HP = TORQUE X RPM / 5252. Again using the recipricating engine, no HP (work) is done unless motion (RPM) is present.

Jim
SR Racing

Work, BY definition requires motion. (at least when discussing an engine), uless your intent is to just develop heat. Obviously by the laws of thermodynamics, the energy is there in some form, but when discussing an engine the work we are interested in is movement.

I concede, and agree that you are right.

The inverse is true
??? "Torque" is a unit of rotational "force." It has nothing to do with "power" or "work".

Yes, Horsepower is just a unit, but it is representative of force and time. (or RPM).

I am still not convinced,

Torque is a rotational force but it is directly proportional to work for a given number of revolutions (time independent). That is for one revolution 1 lb-ft of torque will result in 6.28 ft-lb of work, or a 2 lb-ft torque results in 12.56 ft-lb of work.

Power is going to be torque and revolutions per unit time, or from above simply work per unit time (not force and time; but force, distance, and time).

Also, by saying horsepower is just a unit, my point is that it should not be substituted for the word “power”.

[img=http://img220.exs.cx/img220/502/tqhp9je.th.jpg] (http://img220.exs.cx/my.php?loc=img220&image=tqhp9je.jpg)


i think it looks perdy...except i don't think i have the turbo setup correctly.

edit: yea pic was big but now you can see why there alot of "0"s :)

more edit:I took the race ported flow file and scaled up the flow to match the increased size of the ports over the origional. Its also iinteresting to note that by increasing the flow of the turbo charger the HP decreases. i don't know how one would properly setup the turbo on this.

Theres a lot of "0"s on that grapgh! :eek2:

Torque is a rotational force but it is directly proportional to work for a given number of revolutions (time independent). That is for one revolution 1 lb-ft of torque will result in 6.28 ft-lb of work, or a 2 lb-ft torque results in 12.56 ft-lb of work.

Power is going to be torque and revolutions per unit time, or from above simply work per unit time (not force and time; but force, distance, and time).

Also, by saying horsepower is just a unit, my point is that it should not be substituted for the word “power”.

Maybe semantics? :smile:

Yes, Torque is rotational force that is proportional to work (HP) in the provided formula. Its (torque) presence though, does not mean any work is being done. For example a steam engine produces maximum torque at 0 RPM. All the energy is expended as heat. Thus, 0 HP.

In this engine scenario, the term "horsepower" can certainly be substituted for the word "power". As could be "Watts" or BTU/Hr, or even "pound feet per minute". :smile:

They are all the same. Simply "units" that represent power.

Jim
SR Racing

Maybe semantics? :smile:

I think perhaps you are correct about that so let me state this one more time, just for clarification and not so much as a retort.

Yes, Torque is rotational force that is proportional to work (HP) in the provided formula. Its (torque) presence though, does not mean any work is being done. For example a steam engine produces maximum torque at 0 RPM. All the energy is expended as heat. Thus, 0 HP.

I do agree that at 0 RPM no work is being done, as I was incorrect in my above post.

Yes, Torque is rotational force that is proportional to work (HP)....

...the term "horsepower" can certainly be substituted for the word "power".

I am confused as to why work can be measured in horsepower, and horsepower is an equivalent term for power.

In this engine scenario, the term "horsepower" can certainly be substituted for the word "power". As could be "Watts" or BTU/Hr, or even "pound feet per minute". :smile:

They are all the same. Simply "units" that represent power.

I was taught that when writing about or discussing a technical subject one should use non-unit specific terms were ever possible including equations. Since horespower is imperial system unit specific, power is in general a more accurate term. Also, for example the equation:

Power = Torque x RPM / 5252

is only applicable when power is in “hp” and torque is in ”lb-ft”. The 5252 comes from converting revolutions to radians, minutes to seconds, and lb-ft / s to hp. The general equation for power is actually:

Power = Torque x Shaft-Speed (P=Tn)

I am confused as to why work can be measured in horsepower, and horsepower is an equivalent term for power.

Simply because in this scenario we are discussing usable power (or work) from an internal combustion engine. If we were truly discussing power in a thermodynamics closed system, then certainly any force (or torque) applied would result in the use of power. Even if there were no observed movement, power would be there in the form of heat. Using the steam engine example, while no usable HP is delivered to the wheels the full system energy in = energy out. However the output energy is only heat.

I was taught that when writing about or discussing a technical subject one should use non-unit specific terms were ever possible including equations. Since horespower is imperial system unit specific, power is in general a more accurate term...

And this is a good practice in a physics lab when concerning all energy in vs energy out.

But in a practical engine example we are only interested in work at the flywheel.

Let's assume an electrical engine. If 1000 watts of electrical power were used at the input, some power would result as heat and some as mechanical movement. While this is a 1.35 HP use of energy, it would not result in 1.35 HP of mechanical power. But the total power in vs the total power out would be equal. Maybe 1 HP in output shaft work and another .35HP (or 890 BTU) in heat loss. (Both frictional and electrical resistance.)

I think we have drifted from the thread slightly :smile: , but it was a nice exercise.

As an EE and now owner operator of a chassis dyno and two engine dynos, similar discusions come up with my customers. I try not to get into the conservation of energy laws, since it really doesn't help them much in understanding when to shift from 3rd gear to 4th on the drag strip, or what engine they should use to pull a trailer with. :smile:

Thanks

Jim
SR Racing

Torque is not a force, nor it is a force*distance. Torque is a moment, created by a force acting on a radius multiplied with sinus the angle between the vectors r and F.

A moment can be used to do work, this does however not mean that the moment is work; and if the moment is used to do work, power will be needed. Power is defined as work per time unit and work as a force multiplied with a distance (these are just one of many definitions).
Note that work can't be measured in horsepowers, but horsepower*hour or kWh is possible.

As one can see torque has the same unit as energy/work (N*m in SI units), this do not mean that they are related, becase they aren't. Torque is a vector while energy/work is scalar.

A car can like all bodies be accelerated by F=m*a. The force that accelerated the car is the sum of the torque*radius on all driven wheels, minus the force that is needed to sustain speed.

The force accelerating the car can be highest where the power is highest since most torque per time unit are produced there. However, on any given gear, the force will be highest at peak torque since the gearing will act as a constant torque multiplier.

So for engines power is what's important, torque as a number is not important but the torque curve (or power curve) is important since we can't run the engine on a constant speed (well, you can, but...).
We can for example create the same power using a high speed turbine as using a slow speed piston, the later will create the highest torque but not necessarily the best torque curve.

Also, if we talk piston engines for example; we can create a more powerful engine if we allow ourself to use a more narrow powerband. This is one of the reasons that racing engines are very powerful, but only under a limited rpm range.