torque vs. bhp.
Discussion
A little question that has been puzzling me for a while.
I am looking for a neat, layman's definition of the difference between torque and 'power'. I understand how the difference manifests itself in the driving experience, but don't know exactly what it is. I partly remember an analogy involving a wishing-well and differing sizes of bucket and speeds of lift.
Have i made this up? Can anyone even phrase my question for me, let alone answer it? I'm going to go and lie down...
M
I am looking for a neat, layman's definition of the difference between torque and 'power'. I understand how the difference manifests itself in the driving experience, but don't know exactly what it is. I partly remember an analogy involving a wishing-well and differing sizes of bucket and speeds of lift.
Have i made this up? Can anyone even phrase my question for me, let alone answer it? I'm going to go and lie down...
M
Well with plenty of torque you can accellerate hard at any rpm just by pushing on the pedal, like in a lazy or big yank V8. That won't happen in a zetec but when the zetec's revving it goes well enough because its got a reasonable amount of bhp where it's got higher revs available. Does this help? Torque can shove you into the seat. I like torque as it's very user friendly in daily driving. Racers will probably like revs and bhp.
For straight forward questions I always find this web site to be the best at explaining in an pre O level sort of way ........http://science.howstuffworks.com/fpte3.htm
Works for me.
Harry
Works for me.
Harry
Mikeylad said: Is it possible to have an engine with measurable torque, but zero bhp, or vice versa?
Don't think so as power is a function of torque. IIRC power(bhp) = torque x revs/5250. You can see from this that a high revving engine can produce high bhp without necessarily having high torque. Power gives you speed, torque gives you acceleration. Hope this helps.
GarryM said:
Mikeylad said: Is it possible to have an engine with measurable torque, but zero bhp, or vice versa?
Don't think so as power is a function of torque. IIRC power(bhp) = torque x revs/5250. You can see from this that a high revving engine can produce high bhp without necessarily having high torque. Power gives you speed, torque gives you acceleration. Hope this helps.
That does help, cheers. Also raises another question though. if power is a direct function of torque, how come engines that produce similar power outputs at similar revs can have widely varying torque figures.
By your formula, wouldn't every car producing, say, 200bhp @ 6000 rpm have identical torque figures?
or am i a simpleton? be honest with me. please.
Mikeylad said: That does help, cheers. Also raises another question though. if power is a direct function of torque, how come engines that produce similar power outputs at similar revs can have widely varying torque figures.
By your formula, wouldn't every car producing, say, 200bhp @ 6000 rpm have identical torque figures?
or am i a simpleton? be honest with me. please.
At that precise moment, yes. But the peak torque figure may be at a much lower rev point (therefore not the peak power point).
Think of it this way, power is the ability of an engine to impart more energy to itself, i.e. spin faster.
Torque is the ability of an engine to turn itself under load.
Using gears both these types of rotation can be converted to something useful.
It situations like these it pays to consider extreme examples.
A remote control car engine is low torque, high power. It spins like buggery.
A coach engine is low power V high torque, it has a <3000rpm limit, but an immense ability to do work.
Torque and power are just different ways of describing how an engine produces its output. The end effect is exactly the same (movement) which is why it's so hard to discern between them.
BTW, I made this up, so I may be utterly wrong. But I am meant to be an engineer.
Torque is the ability of an engine to turn itself under load.
Using gears both these types of rotation can be converted to something useful.
It situations like these it pays to consider extreme examples.
A remote control car engine is low torque, high power. It spins like buggery.
A coach engine is low power V high torque, it has a <3000rpm limit, but an immense ability to do work.
Torque and power are just different ways of describing how an engine produces its output. The end effect is exactly the same (movement) which is why it's so hard to discern between them.
BTW, I made this up, so I may be utterly wrong. But I am meant to be an engineer.
Covered all over the place. Cars top speed and ability to accelerate is goverend by the torque - but this is torque at the wheels, not at the engine. So to accelerate, use F=ma and for top speed use acclerating force = drag force, again at the wheels as this is where the energy is transferred from the car to the road.
However, an engine will produce more torque at mid revs, than it does at high revs, but because you are getting more bangs at the higher revs, then the power (torque x rotational speed) will be higher.
So, if you can put the engine at in its maximum power band using the gearbox, you will always have more torque at the wheels, which is good!
This is really end of story.
However, if your engine has more torque at lower revs, then it possibly also has adequate power to achieve acceleration without bothering to change gear. All about how you like to drive really.
Don't think that I could have made that any more confusing, so I'll stop now.
Rich
However, an engine will produce more torque at mid revs, than it does at high revs, but because you are getting more bangs at the higher revs, then the power (torque x rotational speed) will be higher.
So, if you can put the engine at in its maximum power band using the gearbox, you will always have more torque at the wheels, which is good!
This is really end of story.
However, if your engine has more torque at lower revs, then it possibly also has adequate power to achieve acceleration without bothering to change gear. All about how you like to drive really.
Don't think that I could have made that any more confusing, so I'll stop now.
Rich
daydreamer said: Covered all over the place. Cars top speed and ability to accelerate is goverend by the torque - but this is torque at the wheels, not at the engine. So to accelerate, use F=ma and for top speed use acclerating force = drag force, again at the wheels as this is where the energy is transferred from the car to the road.
However, an engine will produce more torque at mid revs, than it does at high revs, but because you are getting more bangs at the higher revs, then the power (torque x rotational speed) will be higher.
So, if you can put the engine at in its maximum power band using the gearbox, you will always have more torque at the wheels, which is good!
This is really end of story.
However, if your engine has more torque at lower revs, then it possibly also has adequate power to achieve acceleration without bothering to change gear. All about how you like to drive really.
Don't think that I could have made that any more confusing, so I'll stop now.
Rich
Aaaargh! My brain!
Correct, if the power curves match, then the torque curves also match.
mikeylad said: i think i might have started something i can't control.
am i right to think that all engine with matching power curves must by definition have matching torque curves?
i can't see any room in the formula for deviation. having said that, i can't see much of anything.
The reason there are pub debates on torque vs power is that the curves don't match. V8 TVR's have bags of torque low down (hence higher power curves in this range too) - I believe that the technical term is grunt
- but the torque drops off up the rev range far more than an S2000 engine, which is sold as a high power engine. Therefore if you don't mind hooning around in the red line area, there is no difference in flexiblity between the two. The bags of torque brigade like to just be able to press the right foot down at 2000 revs to get the car to explode, the high power bunch change gear first.
Mikeylad said: Is it possible to have an engine with measurable torque, but zero bhp, or vice versa?
It wouldn't be much of an engine, if it had non zero torque, but zero power, then by definition the engine would be doing 0 RPM
You can produce a torque with no power, but producing power with no torque is not really possible in practice as no bearings are frictionless, and hence require some torque to turn them.
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