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Nm To Hp


Esher
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It is possible to calculate Horse Power from Torque,but you need to know the RPM that the torque figure was measured at.

 

165Nm torque is about 121lbs/ft torque

 

The formula for HP is:- (Torque(lbs/ft) x RPM) / 5252

 

Frank

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Hii,

 

I think Torque and Horse power are two different characteristics of an engine and cannot be calculated from each other.

 

The formula given here could just be an estimation for a group of engines.

 

cheers

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Hii,

 

I think Torque and Horse power are two different characteristics of an engine and cannot be calculated from each other.

 

The formula given here could just be an estimation for a group of engines.

 

cheers

44459[/snapback]

Horsepower and torque are both measurements of work done and are directly related to one another. Here are some explanations.

 

http://www. car-videos. com/articles/horsepower_torque. asp

 

http://www. newton. dep. anl. gov/askasci/phy00/phy00260. htm

 

http://www. epi-eng. com/BAS-PwrTrq. htm

 

Frank

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Max power kW/BHP 104/139 @ 6000rpm : 83/111 @ 4000rpm

Torque Nm/lbs ft 184/136 @ 4500rpm : 255/188 @ 2000rpm

 

 

Above are the figures for two models of the same car. One has a petrol engine, one a diesel. Both are 2 litre engines, the diesel has a turbo.

 

 

The petrol engine has a BHP figure of 139, yet a torque (Nm) figure of 184. The diesel has a much lower BHP figure of 111 yet a much higher torque (Nm) figure of 255. It's also noticeable that diesel engines rev much lower.

 

It would seem to me that because maximum torque and maximum BHP are attained at different engine revolutions that any formula is going to give misleading figures.

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Max power kW/BHP   104/139 @ 6000rpm  :  83/111 @ 4000rpm

Torque Nm/lbs ft      184/136 @ 4500rpm  :    255/188 @ 2000rpm

Above are the figures for two models of the same car.   One has a petrol engine, one a diesel.   Both are 2 litre engines, the diesel has a turbo.

The petrol engine has a BHP figure of 139, yet a torque (Nm) figure of 184.   The diesel has a much lower BHP figure of 111 yet a much higher torque (Nm) figure of 255.   It's also noticeable that diesel engines rev much lower.  

 

It would seem to me that because maximum torque and maximum BHP are attained at different engine revolutions that any formula is going to give misleading figures.

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no. torque you can feel, thats the REAL POWER. bhp you cannot thats the max

working rate, you take the torque figure as has already been said, use the fomula

to work out bhp. as you cannot feel bhp, there is no other way to work it out.

 

now if the diesel cars were to rev 1 or 2000 rpm higher, then they would give even greater bhp readings. why do you think racing cars and bikes rev so high?

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. ....... why do you think racing cars and bikes rev so high?

44468[/snapback]

 

They sound better :rolleyes:

 

<I think Torque and Horse power are two different characteristics of an engine and cannot be calculated from each other.>

 

Seriously though there must always be a relationship between the various measurments of output of an engine however one cares to desribe them or what one calls them :unsure:

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Hii,

 

I think Torque and Horse power are two different characteristics of an engine and cannot be calculated from each other.

 

The formula given here could just be an estimation for a group of engines.

 

cheers

44459[/snapback]

 

I think there are some missing points in this discussion. But I should correct myself first :

 

"I think MAX. Torque and MAX. Horse power (which we are usually after, to level an engine performance) are two different characteristics of an engine and cannot be calculated from each other. "

 

 

However for a known rpm and torque, HP output of an engine - at that rpm- can be theoreticaly calculated as given in Frank's formula :

 

"The formula for HP is:- (Torque(lbs/ft) x RPM) / 5252"

 

But be careful this formula cannot satisfy for a given max. torque & max. HP values of an engine, as they cannot appear at the same rpm's in usual.

 

Regards.

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Hi All,

 

My reply to Eshers original question is correct. For a given TORQUE you can calculate the associated HP provided you know the RPM.

 

What you cannot do is calculate HP at one RPM from TORQUE at a different RPM, unless of course you had a mathematical model of the engine in question.

 

Frank

Edited by Frank
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Its a little bit like comparing apples with oranges. They are two different things.

 

Torque is a measure of how much a force acting on an object causes that object to rotate and is expressed in lb ft, newton meters etc

 

Horsepower or power is the rate of doing work and is expressed in lb ft per min.

1 HP is 33,000lbft/min. This was developed by James Watt who worked out that a good dray horse could lift 150lb of coal from a 220ft deep pit in one minute.

 

They are however related by time or RPM and hence as Frank has said you can convert torque to HP for any given RPM.

 

It is also worth noting that the torque quoted is the torque at the engine, which cannot be increased beyond its maximum. Torque at the wheels, however, can be changed by changing gear and it is multiplied by whatever gear ratio you are in. It is torque at the wheels which gives the acceleration. Thus you get the greatest acceleration in first gear and an engine which gives you high torque at low revs (i. e diesel) will give greater acceleration in top gear or greater pulling power for a caravan. Thus when comparing engines it is more useful compare torque than power.

 

Brian

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With all due respect :huh: This thread is begining to sound like the Annual General Meeting of the Nit Picker Society :rolleyes:

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With all due respect :huh:  This thread is begining to sound like the Annual General Meeting of the Nit Picker Society :rolleyes:

44534[/snapback]

 

 

I wouldn't know, I've never attended. .. :D:D

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With all due respect :huh:  This thread is begining to sound like the Annual General Meeting of the Nit Picker Society :rolleyes:

44534[/snapback]

 

 

On the contrary, I find it educational, informative, we are never to old to learn :rolleyes:

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Guest Hobbybod

As Sparkey, and others, suggest torque and power are two quite different parameters and as such are impossible to equate as they possess different dimensions. I'll say no more on that, . . . . you'll be relieved to hear!

 

Horsepower and torque are both measurements of work done and are directly related to one another.

Frank, I'm afraid neither Torque nor Power are measurements of work done; {Power (W)= work done(J)/time(s)}

Although Torque and work done (or Energy) may appear to have similar units i. e. a force (N) x a distance (m) they can not be equated due to differences in definition.

 

The International Unit for torque is Nm or newton. metres whilst the old Imperial unit was ft. lbs. A simple dimensionless conversion factor (i. e. number) can convert from one unit to the other.

It was this sort of conversion that Esher was asking about, I presume.

 

Similarly the International Unit for Power is the Watt (W) while an old Imperial unit is bhp (British Horse Power) used mainly in the automotive industry.

Again a simple numeric conversion factor will convert from one unit to the other.

 

The conversion factors can be worked out from the data Jim gives for his car!

 

Now Frank's formula derives the power from the torque for a single, given rotational speed (rpm).

 

As max power and torque are invariably produced at different rpm such a derivation is of limited use when discussing diesel or petrol engines.

Different for electrical motors.

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Yes Hobby I agree with all your units except Imperial Torque, which is usually expressed as lbf. ft.

 

This is all good background for anyone who has not been involved in the measurement of force and motion and those who wish to extend their knowledge can always read any good physics or mechanical engineering theory text book.

 

However in answer to Eshers original question,it is possible to convert torque to HP given the constraints of a known RPM. :)

 

Where is Esher anyway,he hasn't appeared since asking the question?

 

Frank

Edited by Frank
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For a very good/amusing explanations of these things see:-

 

http://www. pumaracing. co. uk/power1. htm

 

No 'nit-picking' there :wub:

 

PS I did put a smiley face on my last posting WHICH is supposed to mean 'done in a humorous light'

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  • 2 weeks later...

 

Similarly the International Unit for Power is the Watt (W) while an old Imperial unit is bhp (British Horse Power) used mainly in the automotive industry.

Again a simple numeric conversion factor will convert from one unit to the other.

 

44559[/snapback]

 

I think you will find that it's BRAKE horse power as it's is measured by using a brake dynomometer. The European PS is slightly less than bhp.

 

Mike

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I believe BHP is as Mike says Brake Horse Power because it is the measure of how many horse would be needed to stop the engine at the flywheel - but it is now exactly 50 years since my apprenticeship B) so memory is not what it used to be.

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