Sorry, but I'm a little slow on the uptake (& totally blinded by science)and have yet to get an explanation that I can understsand, of what power vs torque actually means in practice.
Suppose car A & car B have the same power, but A has higher torque than B, what difference would I notice in the way they drove?
And if C & D had the same torque, but C had more power, what difference would I notice?
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I think this explains everything: www.pumaracing.co.uk/power1.htm
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Tyro
You're not alone.
My quick & dirty conceptual grasp is that torque = grunt = acceleration. Given the same power (bhp), the car with the greater torque will be quicker to accelerate. But torque is not evenly distributed over the whole range of engine revs, so it depends where you start and where you finish. Torque can be very noticeable in diesels because it is often manifested at relatively low revs; however, it is rarely sustained to high revs. Thus, in the Audi diesel courtesy car that I once drove, its acceleration from less than 1500 rpm to well short of 3000 rpm was most impressive, but there wasn't much point in pressing further without changing gear.
I am reminded of a V12 MB S600 that I saw demonstrated at MB UK HQ at Milton Keynes. Its torque curve has a flat peak between 1800 and 3500 rpm -- at 800Nm! Now, that's what I call "grunt". Its lesser stable mates with less torque may reach the same top speed, but would get there less quickly.
Don't rely on all that, but it works for me -- so far.
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Tyro,
Suppose car A & car B have the same power, but A has higher torque than B, what difference would I notice in the way they drove?
If A has higher torque, but the same power as B, then A must produce this torque lower down in its rev range, and thereafter as revs increase for engine A, its torque would reduce. This is the characterisitic aimed for in commercial vehicle engine design, and explains for the differences in performance of the same sized engines in, say a transit and a sierra. This characteristic, called a "back up" torque characteristic, of having high torque at low engine speeds is useful in commercial vehicles because it allows the vehicle to climb hills easily - as the engine slows it develops more torque, and an equilibrium is reached.
And if C & D had the same torque, but C had more power, what difference would I notice?
This means that D produces its torque lower down the rev range, and it has a "back up" torque charateristic.
Of course, it you are designing an engine for a lighter vehicle, you aren't interested in back up torque, you are more interested in getting a high flat torque curve that remains high as you go up the rev range. Eventually, port/valve aerodynamics stop this, and the torque curve begins to fall. This is the reason for 16V engines, you can get more air through before they begin to choke.
I hope this helps...
number_cruncher
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Tyro
There seems to be too many people trying to baffle you with science!
To answer your question...
To put it simply (that's all it needs!!)... With car 'A' you wouldn't need to change down gears as much when going uphill - it would 'hang on' longer in each gear.
With car 'C' it would be able to go faster than car 'D'
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Taking extremes
You could have a tiny, minature engine spinning very fast producing negligible torque and, say 50 BHP.
You could have a man turning a spanner on the the bolt on the end of the crankshaft producing 100Nm of torque, but no meaningful power.
Both of these are clearly no use to drive a car.
The speed at which an engine produces its peak torque is the important thing. Commercials produce it low down in the rev range, and racing engines, higher. The spread between the max torque engine speed and the max power engine speed give a measure of how flexible an engine is in use.
To digress - how should a Wankel engine be considered? It has some internal gearing. Should power be calculated from the rotational speed of the rotor, or of the output shaft?
number_cruncher
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Okay, thanks guys - it's a bit clearer now. I was always able to relate torque to "grunt", but never really knowing why.
I only ask because I test drove a Civic Type-R and a Focus ST170 on Monday, and thought in comparison the Type-R was pretty gutless below 5500rpm, where the ST170 had grunt much lower down. Though there was the ridiculous surge of power around 7000rpm on the Civic. :o)
Both cars seem to have identical max torques, although the ST achieves it slightly lower down.
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Is it any clearer really?.If you ever want to make a car know all look silly at a party ask him to explain what torque means!LOL! Its impossible to do so!
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Thanks for those who've thrown in their wisdom. I think I'm a little clearer. One day, perhaps I'll understand it all.
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My definition of torque is much simpler and needs no scientific explanation, since it is based on experiential methods.
It's a handful of Harley throttle at the traffic lights and a belt in the guts at quite low rpm allied to serious acceleration causing one to make sure one has a good grip on the bars and one's squeeze on the back seat has a good grip on oneself, while chummy on his Hondayamakawasuzi is winding the bejesus out of his riceburner in an attempt to get some speed up.
He will eventually overtake me (BHP) but his girlfriend back-riding won't enjoy it as much as mine. Has something to do with the vibration I believe.
But then what do I know? I only got 17% in GCE Physics LOL.
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In simple terms, torque is the turning power of the engine, power is speed of delivery of that turning power.
So, lean on a torque wrench that's a foot long with a force of 100lb. Regardless of how fast it rotates, if you're still applying a torque of 100ftlb, the torque is unchanged. However, the faster you're rotating it, the more work you are doing; you're increasing the power. With all (?) engines there comes a point when you can't deliver the 100lb force at the speed required, so the torque reduces. However, the power (or total work being done) may still be increasing, despite the torque having reduced to, say, 90ftlb.
Mathematically, thanks to the miracle of the units used:
Power (bhp) = torque (ftlb) x rpm /5252
You'll notice this means that torque in ftlb = power in BHP at 5252 revs.
A big gap in revs between peak torque revs and peak power is generally a sign of a nice driveable engine. At lower revs you'll have the torque to accelerate, at higher revs the engine will still be delivering the remaining torque effectively to continue the acceleration.
HTH.
V
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Well,
With due respect to everyone else, I think Vin explained it nicely. I can almost understand things now.
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Vin is spot on. That means that on any power and torque graph showing bhp, the power and torque curves should cross at 5252. If they do not, like some from "chip tuning" companies, you know they are made up.
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Vin is spot on. That means that on any power and torque graph showing bhp, the power and torque curves should cross at 5252. If they do not, like some from "chip tuning" companies, you know they are made up.
What?? The manufacturers data for my Audi TDI 110 is maximum torque of 225Nm is between 1700 and 3500 rpm and the maximum power of 81kw or 110 BHP is at 4150 rpm..and another thing is the govenor prevents this engine revving beyond 5000 revs so how can power and torque cross at 5252??
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If torque is cheap, how come diesels cost more than petrols?
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"The manufacturers data for my Audi TDI 110 is maximum torque of 225Nm is between 1700 and 3500 rpm and the maximum power of 81kw or 110 BHP is at 4150 rpm..and another thing is the govenor prevents this engine revving beyond 5000 revs so how can power and torque cross at 5252??"
First of all, as my physics teacher, Mr Campbell, used to say, "Units, you nits!" (by the way, that's meant to take the mickey out of me, not you)
225Nm = 165ftlb. 81Kw = 109BHP.
Thus, your graph would have a peak torque at "Somewhere between 1700-3500" (bit vague, that) of 165ftlb. This line would drop off.
Also, your BHP line would peak at 109BHP at 4150 revs and drop off at a different rate. If your car revved to 5252 revs, the two lines would cross there. The fact that the car's got a rev limiter simply means that you can't rev to 5252 revs, not that the lines wouldn't cross there.
By the way, the whole 5252 figure is just a mathematical oddity. It doesn't mean a thing.
V
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By the way, the whole 5252 figure is just a mathematical oddity. It doesn't mean a thing.
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personally, imo, i would say it means quite a lot.
for those who are asking -
"But where does the number 5,252 come from?", see
auto.howstuffworks.com/question622.htm
or the section " HOW TORQUE AND POWER RELATE " at
www.pumaracing.co.uk/power1.htm
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">> By the way, the whole 5252 figure is just a mathematical oddity. It doesn't mean a thing.
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personally, imo, i would say it means quite a lot."
I was making the point that, for example, if you change the units, the crossover point changes, so there is no real importance in the number itself.
V
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