Is torque really relevant?
Discussion
Gary C said:
The only torque that counts is the torque applied at the wheel hub, all the rest is about getting it there.
Even that's not the end of the story: you might as well say that its the (linear) thrust and velocity at the tyre contact patch that is of ultimate importance, because of course the rolling diameter of the tyre is just another step in the gearing.But there are many ways of getting there, and different genres of engine (including diesel, which is what this thread is about) have characteristic... erm... characteristics that mean it's possible to generalise to some degree.
ddom said:
Gary C said:
Merc 500SL lost power in the 90's when it lost its overfuel facility. Rather than ensuring complete burn, it needed to overfuel and run a bit rich to get the best BMEP, which resulted in some fuel not being burnt. So yes, peak power can be delivered 'rich'
I've never seen an engine make more power than when it was slightly lean. Obviously these chancers who tried to flog all manner of kit with headline numbers were all trying it on, but you couldn't compete in them otherwise they would go pop.ddom said:
I've never seen an engine make more power than when it was slightly lean. Obviously these chancers who tried to flog all manner of kit with headline numbers were all trying it on, but you couldn't compete in them otherwise they would go pop.
Maximum power is always obtained with a rich mixture. Lean mixtures burn more slowly and don't provide as much charge cooling.anonymous said:
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It also skips past the point that many cars (mainly diesels) have a high peak torque figure but a very narrow power band so it absolutely matters what gear you are in. Too high or low and there is nothing there, it's as important as a high revving petrol engine, just different because you need higher gears and make less noise. Admittedly modern diesels tend to have wider bands to play with. If we're talking about a big capacity V8 the point is more valid and that is definitely part of the appeal. But it's still about the curve, not the peak. anonymous said:
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Some cars allow you to accelerate reasonably briskly or maintain speed up a short hill without having to change down 1, 2 or 3 gears when you are travelling at, say 60/70mph. Other cars require a bit more gearstick stirring. We are talking about on a road, not a track. It's not about being allergic to changing gear.
Gad-Westy said:
It also skips past the point that many cars (mainly diesels) have a high peak torque figure but a very narrow power band so it absolutely matters what gear you are in. Too high or low and there is nothing there, it's as important as a high revving petrol engine, just different because you need higher gears and make less noise.
Example which doesn't include diesels - an EP3 Civic Type-R will quite happily pull top gear from 30mph to vmax. Not very hard at first, but cleanly. An Impreza Turbo 2000 won't, because it's below its boost threshold. But the Impreza has more mid range torque, so it's "more flexible", right? The measure of flexibility of "how well does it pull in what would be the wrong gear for a NA petrol" has an inbuilt bias.
otolith said:
Example which doesn't include diesels - an EP3 Civic Type-R will quite happily pull top gear from 30mph to vmax. Not very hard at first, but cleanly. An Impreza Turbo 2000 won't, because it's below its boost threshold. But the Impreza has more mid range torque, so it's "more flexible", right?
The measure of flexibility of "how well does it pull in what would be the wrong gear for a NA petrol" has an inbuilt bias.
Why would you be in top gear at 30mph?The measure of flexibility of "how well does it pull in what would be the wrong gear for a NA petrol" has an inbuilt bias.
MC Bodge said:
otolith said:
Example which doesn't include diesels - an EP3 Civic Type-R will quite happily pull top gear from 30mph to vmax. Not very hard at first, but cleanly. An Impreza Turbo 2000 won't, because it's below its boost threshold. But the Impreza has more mid range torque, so it's "more flexible", right?
The measure of flexibility of "how well does it pull in what would be the wrong gear for a NA petrol" has an inbuilt bias.
Why would you be in top gear at 30mph?The measure of flexibility of "how well does it pull in what would be the wrong gear for a NA petrol" has an inbuilt bias.
Wasn't a recommendation, just a point about how an arbitrary measurement of performance in the wrong gear isn't particularly useful.
otolith said:
MC Bodge said:
otolith said:
Example which doesn't include diesels - an EP3 Civic Type-R will quite happily pull top gear from 30mph to vmax. Not very hard at first, but cleanly. An Impreza Turbo 2000 won't, because it's below its boost threshold. But the Impreza has more mid range torque, so it's "more flexible", right?
The measure of flexibility of "how well does it pull in what would be the wrong gear for a NA petrol" has an inbuilt bias.
Why would you be in top gear at 30mph?The measure of flexibility of "how well does it pull in what would be the wrong gear for a NA petrol" has an inbuilt bias.
Wasn't a recommendation, just a point about how an arbitrary measurement of performance in the wrong gear isn't particularly useful.
Labouring your engine in top gear in a typical 5/6 gear car at 30mph is just a contrived scenario.
otolith said:
Example which doesn't include diesels - an EP3 Civic Type-R will quite happily pull top gear from 30mph to vmax. Not very hard at first, but cleanly. An Impreza Turbo 2000 won't, because it's below its boost threshold. But the Impreza has more mid range torque, so it's "more flexible", right?
The measure of flexibility of "how well does it pull in what would be the wrong gear for a NA petrol" has an inbuilt bias.
Bi or even tri turbo engines (diesel or petrol) pull very hard from low revs. The measure of flexibility of "how well does it pull in what would be the wrong gear for a NA petrol" has an inbuilt bias.
That SQ7 V12 monster pulls like a train from idle
MC Bodge said:
otolith said:
MC Bodge said:
otolith said:
Example which doesn't include diesels - an EP3 Civic Type-R will quite happily pull top gear from 30mph to vmax. Not very hard at first, but cleanly. An Impreza Turbo 2000 won't, because it's below its boost threshold. But the Impreza has more mid range torque, so it's "more flexible", right?
The measure of flexibility of "how well does it pull in what would be the wrong gear for a NA petrol" has an inbuilt bias.
Why would you be in top gear at 30mph?The measure of flexibility of "how well does it pull in what would be the wrong gear for a NA petrol" has an inbuilt bias.
Wasn't a recommendation, just a point about how an arbitrary measurement of performance in the wrong gear isn't particularly useful.
Labouring your engine in top gear in a typical 5/6 gear car at 30mph is just a contrived scenario.
k all about whether one car is more flexible than the other, it just tells you whether that car's gearing and torque curve happens to fit the arbitrary gear and speed you've picked.otolith said:
Yes, the point I am getting at is that measuring acceleration in the wrong gear tells you fk all about whether one car is more flexible than the other, it just tells you whether that car's gearing and torque curve happens to fit the arbitrary gear and speed you've picked.
If the arbitrary gear and speed are a frequently occurring normal combination that, then it's worth mentioning. k all about whether one car is more flexible than the other, it just tells you whether that car's gearing and torque curve happens to fit the arbitrary gear and speed you've picked.I'm not sure what point you are trying to prove.
Some cars cruise along at engine speeds that allow them to accelerate briskly when the throttle is pressed. Some don't.
In a contrived scenario, some cars, off boost, labouring in a high gear at tickover at low speed don't accelerate that well. Fancy that.
Edited by MC Bodge on Tuesday 7th July 13:48
jhoneyball said:
Ah the old power versus torque nonsense argument. Power is usually calculated from torque. Attempting to differentiate between them is just silly.
Power is calculated from torque and revs.Neither peak power nor peak torque will tell the whole story - even when you take gearing into account, it's the area under the curve that makes a difference - but as a broad but usually accurate generalisation, a 'torquey' engine will be more flexible and offer better acceleration (even after allowing for gearing) than a 'peaky' one.
Or perhaps you're trying to tell us that attempting to differentiate between an engine (say a 5-litre TVR Rover V8) that produces a peak power output of 270bhp and peak torque of 300 lb.ft and another (say a tuned N/A 2 litre Duratec) that produces an identical 270bhp but a peak torque of 190lb.ft is just silly, because they will drive just the same?
Edited by Equus on Tuesday 7th July 15:57
MC Bodge said:
otolith said:
Yes, the point I am getting at is that measuring acceleration in the wrong gear tells you fk all about whether one car is more flexible than the other, it just tells you whether that car's gearing and torque curve happens to fit the arbitrary gear and speed you've picked.
If the arbitrary gear and speed are a frequently occurring normal combination that, then it's worth mentioning. k all about whether one car is more flexible than the other, it just tells you whether that car's gearing and torque curve happens to fit the arbitrary gear and speed you've picked.I'm not sure what point you are trying to prove.
Some cars cruise along at engine speeds that allow them to accelerate briskly when the throttle is pressed. Some don't.
Some cars, off boost, labouring in a high gear at tickover at low speed don't accelerate that well. Fancy that.
ks when comparing a turbodiesel and a turbo petrol and a high revving NA petrol. otolith said:
The point is that whether or not that one particular gear and speed happens to be a good one for a given engine and gearbox doesn't tell you whether it's a good car or not. It's a crap metric. It's barely relevant when comparing very similar cars with very similar powertrains, and complete bks when comparing a turbodiesel and a turbo petrol and a high revving NA petrol.
On the contrary, if it is a daily scenario, it is a useful indication.ks when comparing a turbodiesel and a turbo petrol and a high revving NA petrol. Unless you are somebody trying to prove a mi or point on an Internet forum, of course.
MC Bodge said:
otolith said:
The point is that whether or not that one particular gear and speed happens to be a good one for a given engine and gearbox doesn't tell you whether it's a good car or not. It's a crap metric. It's barely relevant when comparing very similar cars with very similar powertrains, and complete bks when comparing a turbodiesel and a turbo petrol and a high revving NA petrol.
On the contrary, if it is a daily scenario, it is a useful indication.ks when comparing a turbodiesel and a turbo petrol and a high revving NA petrol. Corvid-2020 said:
Gary C said:
But personally, I much prefer a low torque high rev engine to any diesel.
3000 rpm "steam" engines, 800,000 hP Gary?Although I must admit my favourite engine every to drive was a "diesel" and that was a bit more torque, so whilst it was only 3,300hP it did have 222 kN.
Though, apparently, asking on a "drivers day experience" on the East Lancashire Railway "How fast does this go in 1st gear" is not the correct respect for a Napier Deltic BR Class 55 Loco.
, those deltic engines are amazing.My favorite engine was the 4AGE
Our turbines at work used to work well in big ships.
Edited by Gary C on Tuesday 7th July 14:27
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