Cjehuk - how do you know this stuff? Fascinating and thanks for posting.
Clearly supports the original poster's view that theres little difference once up and running over some real roads. I tend to agree that a modern 2 litre Diesel is enough on UK roads but hard to disagree with Gordonbennett also.
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I agree with cjhuk.
The other factor is manufacturers claims, i.e. not sure how they would stack up on a rolling road though I would guess that the difference between said Leon and Focus would be less than 14 bhp.
I remember being in convoy with a Civic Type-R, I was in the Mondeo TDCi, pulling out of a 50 limit the Mondeo stormed off in top, the Type-R had to use 4th (out of 6) just to keep up, of course the Type-R could have zipped by via 3rd gear (perhaps 2nd even) and hanging it out to 7000 rpm +.
Economy aside the FocuST offers the best of both worlds you can drive it like a TD loads of torque from below 1500 rpm (320nm at 1800) and then flies at the top end hence it is superb at overtaking, you dont have to change down, you can just use the torque though if you do change down you have an even bigger safety margin. As I say, economy aside.
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Cjehuk - how do you know this stuff? Fascinating and thanks for posting.
4 year Masters in Manufacturing Engineering and Management. I did a module on Internal Combustion Engines as an extra... Plus a life long obsession with Engines/Planes/Cars/Trains etc etc.
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of our current resident troll >>
I wondered that, never before has so much garbage been so free of spellin' errors.
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Arn't speelcheckers great! They even work on rubbish. :)
Edited by Old Navy on 23/01/2010 at 12:59
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>>kW = (Torque Nm * RPM / 5252)
This equation as given isn't right.
Power (kW) = Torque (Nm) * angular velocity (radians per second)
This derives quite simply from the work done being the product of torque and angle turned through.
One revolution is 2*pi radians, and there are 60 seconds in a minute, so
Power (kW) = Torque (Nm) * RPM * 2* pi /60
which can be written approximately as;
Power (kW) ~ Torque (Nm) * RPM /10
The 5252 in the original equation is simply a quirk of the perverse units being used (although I acknowledge they are more in more common by non-professionals)
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NC is correct. My bad there - please ignore my assertion in metric units. I goofed.
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The 5252 in the original equation is simply a quirk of the perverse units being used (although I acknowledge they are more in more common by non-professionals)
Agree on the UK and US's apparent love of perverse units, I guess most people don't have to actually calculate answers too often and then there's the French connotations of SI units to consider ?
Back to the OP, as I've had more and more powerful cars I've felt much less of a need to drive quickly, but perhaps I'm just getting old(er).... De-badged (due to their driver's ego perhaps) M-Sport 318i/d BMs and 1.9PD S-Line Audi's storming down the fast lane always make me smile though so I am guilty of conceit.
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ive owned half a dozen petrol cars and my current car has 134 bhp, the highest so far. However the most entertaining car i have drove is a fabia 2 1.4tdi. Nippy, good pickup, higher driving position and that engine noise, wow!
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>>The 5252 in the original equation is simply a quirk of the perverse units being used >>
Torque x (2x Pi) x rotational speed however because the rotational speed (angular velocity) is measured in time, i.e. rpm, then torque is quoted as lb ft/min or Nm/min. 33,000 is conversion factor for lb ft to hp enabling torque to be quoted as a static force, 33000 / (2 x Pi) = 5252.11, this is rounded to 5252.
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Torque x (2x Pi) x rotational speed >>
Of course I mean power = torque x (2x Pi) x rotational speed ... ....
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Torque x (2x Pi) x rotational speed however because......
I think that proves the point very well.
Compare with;
One Watt = One Newton metre multiplied by One radian per second
No fiddle factors, no 33,000, no 5252.
Yes, SI isn't a British system, but I wouldn't mind if the system had come from Mars, it would still be my system of choice for engineering calculations. The French do tend to use some odd prefixes, where I tend to stick to multplies of 10^3.
It's only when doing work for American customers that I use anything other than SI, and it's always a serious PITA.
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Fine NC if you want to quote watts, KW etc though where the requirement is to present torque as a static force then NM/sec or lb,ft/sec need to be converted.
5252 relates to lb,ft, a different figure (7180 IIRC) relates to NM.
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33,000 is conversion factor for lb ft to hp enabling torque to be quoted as a static force, 33000 / (2 x Pi) = 5252.11, this is rounded to 5252. >>
Fine NC if you want to quote watts, KW etc though where the requirement is to present torque as a static force then NM/sec or lb,ft/sec need to be converted. >>
cheddar: What do you mean by "torque as a static force"?
5252 relates to lb,ft, a different figure (7180 IIRC) relates to NM. >>
I think 5252 comes about due to the definition of Horse Power by James Watt as 33000 foot-pound-force per minute.
Now SI units define 1 Watt as 1Nm per second.
If you instead of "per second" you wish to use RPM in your calculation, then
1 Watt = Torque (Nm) x Revs (RPM) x [2pi /60]
now [2pi/60] = [1/9.549] ; so
1Watt = Torque (Nm) x Revs (RPM) / 9.549
to convert Watts to kW, divide by 1000, so
1kW = Torque (Nm) x Revs (RPM) / 9549
or rounded
1 Watt ~ Torque (Nm) x Revs (RPM) / 10
1kW ~ Torque (Nm) x Revs (RPM) / 10,000
So it seems my figure for kW is out by a factor of 1000 compared to NC's example.
I can't see where I have gone wrong.
This is the problem with SI units, you cannot get a feel for whether you are right or if you have made an error of 10 or 100 or 1000 fold. In medicine, it is often the case that where an over-dose or under-dose has been given to a patient, it is due to confusion between micro, milli and centi litres (or grams).
EDIT: just found this useful website
craig.backfire.ca/pages/autos/horsepower
Edited by jbif on 24/01/2010 at 14:44
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cheddar: What do you mean by "torque as a static force"?
jbif, I mean the ability to quote xx lb,ft or NM rather than lb,ft/sec or NM/sec, i.e. taking out the angular velocity. After all xx lb,ft/sec at 1800rpm is rather confusing.
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jbif, I mean the ability to quote xx lb,ft or NM rather than lb,ft/sec or NM/sec, >>
? no comprendo.
Torque is always quoted as Nm or lb-ft (or other units of force x distance).
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jbif, further up, I did write kW, where I should have written W
However,
>>One Watt = One Newton metre multiplied by One radian per second
is right.
>>you cannot get a feel for whether you are right
The best way to avoid this is always to work in basic units - metres, kilogrammes, seconds, and then only at the end of the calc use a modifier like milli or micro.
I've no idea what Cheddar's on about either, it makes no sense at all.
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jbif, further up, I did write kW, where I should have written W >>
Phew! As I said, it is easily done, and illustrates my point about the danger of SI units.
The best way to avoid this is always to work in basic units - metres, kilogrammes, seconds, >>
Agreed. That is what I do, most of the time anyway.
There was something to be said[*] for pounds, stones, hundredweight, slugs, poundals, etc.
[*] good or bad, I won't say.
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I've no idea what Cheddar's on about either it makes no sense at all.
NC, jbif,
Power = torque x rotational speed x (2 x Pi).
The conversion factor is based on 1hp = 33000 lb,ft/min so enables torque to be quoted as a static force without the need to apply rotational speed.
33000 / (2 x Pi) = 5252.11, this is rounded to 5252.
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torque to be quoted as a static force >>
AFAIK, Torque is not a force, whether you call it static or dynamic.
Simply defined, torque is a product of force applied at a distance from the axis/pivot-point.
Sometimes Mechanical Engineers refer to Torque as "Moment".
Another definition of torque is that it is the rate of change of an object's angular momentum.
The link below is NASA's attempt at explaining "torque".
www.grc.nasa.gov/WWW/K-12/airplane/torque.html
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>>so enables torque to be quoted as a static force without the need to apply rotational speed.
No, you're really confused on this issue.
Torque is torque - just like friction is friction!
>>lb,ft/min
That isn't a unit of torque, it's a weird and wonderful unit of power.
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No you're really confused on this issue.
You are doing your best !
>>lb ft/min That isn't a unit of torque it's a weird and wonderful unit of power.
Not weird and wonderful, rather how power would be indicated without appling the conversion factor. As I have said power = torque x (2 Pi) x rotational speed, if the torque is in lb,ft and the rotational speed in rpm, then the result is in lb,ft/min. The conversion factor 1hp = 33000 lb,ft/min enables torque and rotational speed to be converted into HP.
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Surely lbft/min is wrong, it should be lbft x (360-degree revolustions) / minutes.
If I apply 150 lbft to a bolt for a minute I have produce no power unless the bolt turns.
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Just like a jet engine producing say 10,000 lbs of thrust, it is producing no power when the aircraft is at rest.
Edited by lotusexige on 25/01/2010 at 10:13
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Surely lbft/min is wrong it should be lbft x (360-degree revolustions) / minutes.
That part isn't wrong.
In the SI version,
One Watt = One Newton metre * One radian per second
The measure of angle, the radian, is dimensionless as it is a ratio of two lengths, namely the arc length divided by the radius.
You may find the use of radians odd, but, I bet that you learnt an equation using radian measure when you were very small. If you have learnt that the circumference of a circle is 2pi multiplied by the radius, then, the 2pi expresses the angle turned through as radians;
So,
2pi radians = 360 degrees
pi radians = 180 degrees
etc, etc
and C = 2pi * r is just a specific case of the more general formula S = theta * r, where S is the arc length, r the radius, and theta, the angle in radians.
In science and the more technical side of engineering, radinas are always used in preference to more arbitrary units of angle like degreees.
So, in terms of units, Watts are equvalent to Nm/s - there's no need for the angular measure to appear at all.
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