RE: Driven: Audi S8
Discussion
jamesbhp said:
But you all know nothing, as I think you'll find, according to Greenpeace, all of VW group is evil.
http://www.vwdarkside.com/
Oh lordy, what misguided nonsense..http://www.vwdarkside.com/
It is so depressing. People parade lies and half truths as facts and everyone accepts them.
In a couple of generations from now, people will look back at nonsense like this ( as we shiver from global cooling ) and think WTF !!
" It's clever stuff, this shutting down of cylinders: depending on how consistently or gently you're driving, and as long as you're running between 960 and 3500rpm, the S8 becomes a four-cylinder car. And Audi reckons this is worth a 10 per cent improvement in fuel economy during normal, everyday driving."
Out of interest, why is it only a 10% saving when you go from 8 to 4 cylinders? I achieved a good grade in GSCE Maths, but can't work this out. Should it not save 50%? 10% just doesn't seem that much (in fact Audi claim 10% so it is probably less!!)
Anyone?
ETA - Granted it may not be 50% due to a few factors; but I was expecting more than 10%.
Out of interest, why is it only a 10% saving when you go from 8 to 4 cylinders? I achieved a good grade in GSCE Maths, but can't work this out. Should it not save 50%? 10% just doesn't seem that much (in fact Audi claim 10% so it is probably less!!)
Anyone?
ETA - Granted it may not be 50% due to a few factors; but I was expecting more than 10%.
Edited by OdramaSwimLaden on Wednesday 12th October 20:11
Riggers said:
thewheelman said:
I think you'll find the lowest drag coeffiient in this class is the Lexus LS600h, which is 0.27. If it's a luxury, powerful & fuel efficiet barge you want, you'd be mad to not consider the big Lexus. A combined output rating of 439bhp & 30+mpg is pretty impressive.
When Audi says 'in its class' it means XJ supersport and merc S63. And possibly BMW 760iL. it doesn't count the LS600h as a rival for the S8. Edited by thewheelman on Wednesday 12th October 15:10
(But FWIW I think you're right
)
toppstuff said:
jamesbhp said:
But you all know nothing, as I think you'll find, according to Greenpeace, all of VW group is evil.
http://www.vwdarkside.com/
Oh lordy, what misguided nonsense..http://www.vwdarkside.com/
It is so depressing. People parade lies and half truths as facts and everyone accepts them.
In a couple of generations from now, people will look back at nonsense like this ( as we shiver from global cooling ) and think WTF !!
ks make me feel like going seal clubbing......<sarcasm>
OdramaSwimLaden said:
" It's clever stuff, this shutting down of cylinders: depending on how consistently or gently you're driving, and as long as you're running between 960 and 3500rpm, the S8 becomes a four-cylinder car. And Audi reckons this is worth a 10 per cent improvement in fuel economy during normal, everyday driving."
Out of interest, why is it only a 10% saving when you go from 8 to 4 cylinders? I achieved a good grade in GSCE Maths, but can't work this out. Should it not save 50%? 10% just doesn't seem that much (in fact Audi claim 10% so it is probably less!!)
Anyone?
ETA - Granted it may not be 50% due to a few factors; but I was expecting more than 10%.
anyone??Out of interest, why is it only a 10% saving when you go from 8 to 4 cylinders? I achieved a good grade in GSCE Maths, but can't work this out. Should it not save 50%? 10% just doesn't seem that much (in fact Audi claim 10% so it is probably less!!)
Anyone?
ETA - Granted it may not be 50% due to a few factors; but I was expecting more than 10%.
Edited by OdramaSwimLaden on Wednesday 12th October 20:11
Cruising at 70mph the engine has to produce say, 100bhp. The engine isn't trying very hard, so this means that each cylinder isn't operating very efficiently because they only need to produce a tiny amount of power each. Consequently each cylinder is operating outside of it's optimum performance envelope.
Cut down half the number of cylinders and the engine still has to produce 100bhp, but the fuel combustion needed is spread across 4 cylinders instead of 8. This means that each of these 4 cylinders is working harder, but cruicially within they're most efficient performance envelope. This is where the fuel saving comes from.
What detracts from it and reduces what you think the effciency gains ought to be is the fact there's still 8 cylinders worth of engine to turn and the air pumping losses (assuming no valve deactivation) associated with that.
Cut down half the number of cylinders and the engine still has to produce 100bhp, but the fuel combustion needed is spread across 4 cylinders instead of 8. This means that each of these 4 cylinders is working harder, but cruicially within they're most efficient performance envelope. This is where the fuel saving comes from.
What detracts from it and reduces what you think the effciency gains ought to be is the fact there's still 8 cylinders worth of engine to turn and the air pumping losses (assuming no valve deactivation) associated with that.
OdramaSwimLaden said:
" It's clever stuff, this shutting down of cylinders: depending on how consistently or gently you're driving, and as long as you're running between 960 and 3500rpm, the S8 becomes a four-cylinder car. And Audi reckons this is worth a 10 per cent improvement in fuel economy during normal, everyday driving."
Out of interest, why is it only a 10% saving when you go from 8 to 4 cylinders? I achieved a good grade in GSCE Maths, but can't work this out. Should it not save 50%? 10% just doesn't seem that much (in fact Audi claim 10% so it is probably less!!)
Anyone?
ETA - Granted it may not be 50% due to a few factors; but I was expecting more than 10%.
Turn that question on its head - why does it get any better at all? You need a set amount of power to push a given car through the air at a given speed, why does a bigger engine use more fuel to generate that power? Out of interest, why is it only a 10% saving when you go from 8 to 4 cylinders? I achieved a good grade in GSCE Maths, but can't work this out. Should it not save 50%? 10% just doesn't seem that much (in fact Audi claim 10% so it is probably less!!)
Anyone?
ETA - Granted it may not be 50% due to a few factors; but I was expecting more than 10%.
This new S8 sure looks good, the longer chassis improves the Audi family silhoette but it's still closer in looks to an A4 than a C-Class is to an S-Class. If it was a modern luxobarge I was after I reckon the LS or S-Class would get my vote. If this sells it maybe just on price as I can't see it pinching too many sales from Merc with the new forthcoming S-Class.
kambites said:
OdramaSwimLaden said:
" It's clever stuff, this shutting down of cylinders: depending on how consistently or gently you're driving, and as long as you're running between 960 and 3500rpm, the S8 becomes a four-cylinder car. And Audi reckons this is worth a 10 per cent improvement in fuel economy during normal, everyday driving."
Out of interest, why is it only a 10% saving when you go from 8 to 4 cylinders? I achieved a good grade in GSCE Maths, but can't work this out. Should it not save 50%? 10% just doesn't seem that much (in fact Audi claim 10% so it is probably less!!)
Anyone?
ETA - Granted it may not be 50% due to a few factors; but I was expecting more than 10%.
Turn that question on its head - why does it get any better at all? You need a set amount of power to push a given car through the air at a given speed, why does a bigger engine use more fuel to generate that power? Out of interest, why is it only a 10% saving when you go from 8 to 4 cylinders? I achieved a good grade in GSCE Maths, but can't work this out. Should it not save 50%? 10% just doesn't seem that much (in fact Audi claim 10% so it is probably less!!)
Anyone?
ETA - Granted it may not be 50% due to a few factors; but I was expecting more than 10%.
thewheelman said:
Roop said:
Riggers said:
thewheelman said:
I think you'll find the lowest drag coeffiient in this class is the Lexus LS600h, which is 0.27. If it's a luxury, powerful & fuel efficiet barge you want, you'd be mad to not consider the big Lexus. A combined output rating of 439bhp & 30+mpg is pretty impressive.
When Audi says 'in its class' it means XJ supersport and merc S63. And possibly BMW 760iL. it doesn't count the LS600h as a rival for the S8. Edited by thewheelman on Wednesday 12th October 15:10
(But FWIW I think you're right
)OdramaSwimLaden said:
....because it is a bigger engine. Fuel to 8 cylinders will use more fuel than 4 cylinders (assuming the same amount of fuel to each variation)
That doesn't answer the question - why would a bigger engine need more fuel to generate the same amount of power? The fuel contains a set amount of energy per unit volume so to generate a given amount of power you need a certain amount of fuel per unit time, irrespective of the swept combustion volume. The only advantage cylinder deactivation gives you is more efficient burning of the fuel - ie a higher proportion of the fuel injected into the cylinder goes towards pushing the piston down. Explaining why cylinder deactivation helps at all, is quite complicated.
Edited by kambites on Thursday 13th October 08:59
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