omega0684
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| posted on 10/9/09 at 09:29 PM |
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torque
can someone please explain 'Engine Torque' to me please, i know that cars are measured as having brake horse power and
'Torque', but how is it measured and what is it referenced too? what are good torque figures and what are bad torque figures?
i've heard people say that diesels have more torque than petrol powered cars, but why, is it only in the event of having a turbo diesel etc?
cheers
[Edited on 10/9/09 by omega0684]
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graememk
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| posted on 10/9/09 at 09:33 PM |
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Graeme goes to google to find the answer.
i was going to copy and paste the results in order to make myself look cool and cleaver, but cant be arsed as i'm on the wine.
so heres a web link to look at.
http://www.streetrodstuff.com/Tech_Stuff/Tech_Terms_II.php
[Edited on 10/9/09 by graememk]
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omega0684
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| posted on 10/9/09 at 09:46 PM |
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thats a very poor explanation IMO, i posted on here cuz i know i would get a thorough well explained answer 
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graememk
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| posted on 10/9/09 at 09:46 PM |
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sorry i'm drunk....
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Jasongray5
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| posted on 10/9/09 at 09:52 PM |
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Torque is the turning force of an engine. Its measurse in a weight x distance. For example ft/lb's so an engine with 80ft/lb's has a
turning force of 1lb at a distance of 80ft?
A diagram would explain better, but I know what I mean??
How hard can it be?
http://www.flickr.com/photos/33261515@N03/sets/72157611049241239/
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smart51
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| posted on 10/9/09 at 09:53 PM |
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torque is a turning force. Think of a chinese burn. If you want to tighten a bolt, you apply more torque.
You're familiar with force = mass times acceleration. Torque = mass times rotary acceleration. given a rotary thing, lets say the roller on a
dyno, of a certain mass plus a means of measuring the its speed against time, you can calculate the torque needed to accelerate that mass.
Now work done = force times distance. Torque is a turning force so work done = torque times turning. Power = work done per second so power = torque
times revs.
more torque (at the wheels) = more acceleration (of the wheels), with the proviso that your tyres still grip the road. Too much torque and all you
get is wheel spin. Torque to weight ratio governs your acceleration.
Now diesels don't rev as high as petrols. We've discussed that power = torque x revs. If a diesel makes the same torque as a petrol, it
will make less power because it doesn't rev as high. In a given car, the standard fit diesel engine is either bigger in capacity or has a turbo
or both compared with the petrol, to give similar power output (compare a 1.4i citroen to a 1.4tdi for exanmple - about 75 BHP each). This being the
case, the turbo diesel will have more torque but the same power as the NA petrol.
This only really makes a difference in 1st gear, which will be a similar ratio. Ratios are wider spaced on the diesel to counter the lower revs.
Torque at the wheel = torque at the flywheel / gear ratio. So an equally powered diesel may get the jump off the line compared with its petrol twin,
but the petrol's longer legs will see it catch up and slowly overtake. Equal power means equal top speed, but the petrol will get there
slightly sooner.
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NigeEss
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| posted on 10/9/09 at 10:03 PM |
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As mentioned, torque is a measure of force.
Someone here has a footnote that sums it up perfectly but alas I can't remember who. Sorry to that person
But to quote.............
Power/BHP is how fast you hit the wall....
Torque is how far you ake the wall with you !
Unquote..................
Time is an illusion. Lunchtime doubly so.................Douglas Adams.
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Steve Hignett
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| posted on 10/9/09 at 10:09 PM |
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If you tighten a wheel with your 1/2 " ratchet and go really quick, that may be considered more Hp, the quicker you turn your arm, but the more
leverage you apply (a breaker bar) the more torque you are exerting on that bolt...
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brianthemagical
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| posted on 10/9/09 at 10:28 PM |
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Torque is force times distance, hence to tighten a bolt up more, which we know means it's got more torque/been torqued to a higher value, you
need a longer bar or more force. this equates to engines as they are simply a lever and a force. the leaver being the crank, with the big end a
distance-half the stroke- form the mains. the force is the combustion process, via the piston/conrod. as we know a certain capacity uses a certain
amount or air and fuel, thus a very similar power per revolution, in a long stroke engine this gives more torque simply due to the crank dimesions.
more power comes from the revs, with a shorter stroke engine being able to rev higher due to the lower piston speeds afforded by it's short
distance.
power is a factor of the frequency of a force. more revs, more combustion, more fuel being used therefroe, within reason, we can assume more
'power' or working force is being converted, hence power being faster than torque.
think of it as a hammer. lots of little taps is more power, one big tap is more torque. both get the nail in, but if the nail needs a hit of strength
10 to move, and the lighter taps are only 5, then it'll never move.
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Madinventions
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| posted on 10/9/09 at 11:35 PM |
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Yep - agree with all the above.
It can sometimes help to 'visualise' the torque. For instance, my Mazda Diesel estate has 300Nm of torque: That means that if it had 1
metre radius wheels (it doesn't...) then it could push/lift/move 300N of weight (about 30Kg ish). Measure your arm, and work out what weight
that's equivalent to you holding. My arm is approx 500mm from should to grip so it'd be like me holding a 60kg weight at full stretch.
Hmmm...
As an aside, my Mojo has 110Nm of torque from it's mighty 1.25 Zetec SE with 75BHP. The Mazda is 300Nm of torque and 136BHP. The Mojo is about
twice as quick 0-60, probably because it weighs 523Kg and the Mazda is >1500kg, but remember it's rolling weight your torque is pushing. I
can push the Mojo with one hand, but the Mazda needs a lot more grunt!
Ed.
Mojo build diary: http://www.madinventions.co.uk
Solo music project: Syrrenfor http://www.reverbnation.com/syrrenfor
View my band website:
http://www.shadowlight.org.uk
http://www.eastangliankitcars.co.uk/
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blakep82
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| posted on 10/9/09 at 11:56 PM |
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quote:
Originally posted by NigeEss
But to quote.............
Power/BHP is how fast you hit the wall....
Torque is how far you ake the wall with you !
Unquote..................
i thought it was the other way around?
ie more torque gives you better acceleration, and power is how well you keep the speed up if something tries to slow you down?
________________________
IVA manual link http://www.businesslink.gov.uk/bdotg/action/detail?type=RESOURCES&itemId=1081997083
don't write OT on a new thread title, you're creating the topic, everything you write is very much ON topic!
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jeffw
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| posted on 11/9/09 at 05:38 AM |
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The important thing to remember about torque and cars is that you cannot out accelerate the torque curve. The shape of the torque dictates how the
car drives.
My RS4 had 530 ft/lb (718Nm) at 4000rpm. This is made up of a very sharp rise in torque at around 2750 where the turbos start to work upto the peak
and then a steady decline down to the redline. The sharp rise in torque gives you the kick in the back. My A6 3.0Tdi has a completely different
torque curve which peaks at 415 ft/lb (562 Nm) at 2000 rpm but stays within 10% of that until 4250rpm. This gives you the classic diesel flat
curve.
The other thing to remember is that rolling roads only measure torque. The BHP or Wheel HP figure is a calculated number from the measured torque.
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clairetoo
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| posted on 11/9/09 at 05:59 AM |
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As Carroll Shelby once said
"Horsepower sells cars , but torque wins races"
Its cuz I is blond , innit
Claire xx
Will weld for food......
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alistairolsen
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| posted on 11/9/09 at 07:00 AM |
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quote:
Originally posted by blakep82
quote:
Originally posted by NigeEss
But to quote.............
Power/BHP is how fast you hit the wall....
Torque is how far you ake the wall with you !
Unquote..................
i thought it was the other way around?
ie more torque gives you better acceleration, and power is how well you keep the speed up if something tries to slow you down?
All of these quotes, and the shelby one are all nutsack tbh.
Also remember that a single torque figure and power figure are fairly meaningless.
Take for instance a 1000cc 150bhp bike engine making 80ftlbs at 12krpm and a 2000cc 150bhp car engine making 160ftlbs at 6000rpm. Conventional wisdom
would say that with the appropriate gear ratios they would produce exactly the same effect at the wheels, but the bike engine will have much less area
under the torque (and hence power) curves making it much more peaky to drive and overall slower in use.
My Build Thread
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stevec
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| posted on 11/9/09 at 07:18 AM |
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Torque is the distance you travel through a wall after you hit it.
Steve.
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alistairolsen
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| posted on 11/9/09 at 07:40 AM |
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quote:
Originally posted by stevec
Torque is the distance you travel through a wall after you hit it.
Steve.
no, thats momentum 
My Build Thread
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stevec
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| posted on 11/9/09 at 07:49 AM |
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to you as well.
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alistairolsen
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| posted on 11/9/09 at 08:12 AM |
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Sorry, just these bullshit explanations of torque and power really do me in cos people just repeat them parrot fashion with no clue as to whether
theyre correct or not.
torque is turning force
rpm is speed
power is a function of the two.
Caroll Shelby was wrong, its area under power the curve that wins races. His point that peak power isnt everything is however true.
My Build Thread
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flak monkey
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| posted on 11/9/09 at 08:23 AM |
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Simples
Exactly as Alistair says. The 2 are intrinsically linked.
If you want a basic explaination in terms of performance. Torque gives you acceleration and BHP gives you top speed. The rate of acceleration is
linked to the torque curve.
Sera
http://www.motosera.com
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alistairolsen
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| posted on 11/9/09 at 08:37 AM |
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yes and no, its quasistatically linked to the torque at the wheels at some point in time for which you want the instantaneous acceleration, but
overall its related to the bhp which indicates the rate at which work can be done.
also worth remembering when trying to make comparisons that only the torque and power at the wheels are of any great relevance in a direct comparison
due to gear ratios etc.
My Build Thread
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02GF74
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| posted on 11/9/09 at 08:47 AM |
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quote:
Originally posted by alistairolsen
Sorry, just these bullshit explanations of torque and power really do me in cos people just repeat them parrot fashion with no clue as to whether
theyre correct or not.
My parrot could torque.
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smart51
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| posted on 11/9/09 at 09:44 AM |
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quote:
Originally posted by stevec
to you as well.
That's the best thing I've ever seen on a forum. The use of an emoticon as an insult.
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blakep82
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| posted on 11/9/09 at 11:26 AM |
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quote:
Originally posted by smart51
quote:
Originally posted by stevec
to you as well.
That's the best thing I've ever seen on a forum. The use of an emoticon as an insult.
insult on a primary school level too
________________________
IVA manual link http://www.businesslink.gov.uk/bdotg/action/detail?type=RESOURCES&itemId=1081997083
don't write OT on a new thread title, you're creating the topic, everything you write is very much ON topic!
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MikeR
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| posted on 11/9/09 at 11:38 AM |
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My simplistic view (and whilst i appreciate before it wasn't 100% accurate now i'm not even sure if its 20% accurate) is ....
Torque is the cars ability to pull a weight,
HP is the cars ability to accelerate that weight.
So F1 car with sod all torque but lots of HP goes damned fast
Large truck with relatively little HP but lots of torque pulls lots of weight.
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MikeRJ
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| posted on 11/9/09 at 11:55 AM |
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quote:
Originally posted by flak monkey
If you want a basic explaination in terms of performance. Torque gives you acceleration and BHP gives you top speed. The rate of acceleration is
linked to the torque curve.
As Alistair says, this is a bit of a misleading explanation. The thing that gives you acceleration is torque at the wheels, not the crank. The gear
ratios between the engine and wheels (i.e. the torque multiplier) are just as important as the engine specifications.
This is something diseasal drivers don't seem to realise; they like to talk about the torque their engines produce, but these engines have a
very limited RPM range so they have tall final drives (less torque multiplication). The torque at the wheels is therefore less impressive than the
engine specs might suggest.
Even the "area under the curve" is only important because of the limitations of conventional transmissions. If reliable, wide range
continuously variable transmissions were available the peakiness of the engine would be inconsequential, since it could just run at peak power and the
transmission would always deliver optimal torque to the wheels. This is why hybrid technology is moving toward solutions with no mechanical linkage
between engine and wheels, instead the engine drives a generator just like a diesel-electric locomotive. It means the engine can run at a constant
RPM where it is tuned to be most efficient.
Every car forum I visit has had long, protracted threads on the difference between torque and BHP, and the same misleading (and some total BS)
explanations get recycled again and again. I am honestly stumped as to why people find this such a difficult topic to grasp, it's really very
basic physics, hardly even GSCE level stuff.
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