www.thule.com/Thule/Page____90595.aspx
this diesel Astra is getting nowhere near some of the mpg figures posted on here a short while back on the fuel economy thread...:-)
Edited by Westpig on 22/05/2009 at 11:20
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If my 96 Astra 1.7d estate drops below 50 mpg I want to know the reason. I thought mpg was supposed to be getting better.
Why should I want to scrap it for a new one with nearly twice the fuel consumption?
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Thanks for the link;o) there was no shocks there for me. I'd have liked them to have repeated the test with a modern 16V non turbo car too for a comparison
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I find that quite fascinating. I have noticed the difference between drinving speeds on the motorway myself, but with an engine the size of mine the aircon makes very little difference.
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I too have noticed that low tyre pressure = poor mpg is a myth, well certainly at urban and extra urban speeds. I think it may make a noticeable difference the further over 60mph you go as the rolling resistance increases exponentially with speed.
Edited by Hamsafar on 22/05/2009 at 12:20
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>>increases exponentially with speed.
No it doesn't.
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Note the uneven fall off with speed:
60 mph - 52.4 mpg
70 mph - 42.3 mpg - 10.1 less than 60 mph
80 mph - 39.7 mpg - 2.5 less than 70 mph
90 mph - 36.1 mpg - 3.6 less than 80 mph
which suggests some interesting drag/aerodynamic issues with increasing speed.
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SQ
which suggests some interesting drag/aerodynamic issues with increasing speed.
Or a nice spread of peak torque from 70 - 90
Edited by Dynamic Dave on 22/05/2009 at 13:51
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Note the uneven fall off with speed:
That confused me too. I would have expected the difference to increase with each 10 mph.
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>>which suggests some interesting drag/aerodynamic issues with increasing speed.
I wonder if the odd figures are because the turbo is beginning to have a larger effect at these engine speeds.
I'm fairly sure we would be able to see what's going on if a proper engine performance map were published.
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Interesting indeed. Although the go slower / get more mpg finding, while generally true, is a little bit misleading because on the testing ground they're not being baulked by other traffic.
On a typical busy daytime motorway you can usually maintain a constant 50 / 55 (i.e. not overtaking any trucks) or a constant 80+mph (i.e. in lane 3 and avoiding trucks altogether).
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"Or a nice spread of peak torque from 70 - 90"
Torque at a specific rpm will improve acceleration, but will it improve mpg?
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driving slower may not actually reduce fuel consumption.
On my journey to and from work there is a steep hill at motorway speeds that rises over 250 feet in less than a quarter of a mile.
If I drive up it at 60mph I am sure I use more fuel than driving up it at 70mph.
(The engine is in the middle of its torque band at 70mph and not at 60mph).
Real life economy is a lot different compared to 'tested' conditions
Edited by diddy1234 on 22/05/2009 at 13:02
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I am sure I use more fuel than driving up it at 70mph.
Unfortunately 'I am sure that ..' is not a scientifically convincing statement without some sort of evidence.
Interesting that the article effectively says that the only factor they found which made a big difference to economy is driving speed. I suspect the Mk-1 air-con units put more drain on the electrics than current versions.
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Andrew-T, I have tried tank for tank (in my old petrol car) driving up the same hill and can say that if the engine is in its optimal torque for climbing a steep hill then less fuel is used (even if this means driving at a slightly higher speed).
Hence my point is that driving slower doesn't always save fuel.
The real world conditions have to be taken into account.
Time will tell with my new diesel engined car how the economy is handled at climbing the same hill at the same speeds.
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A steep hill at motorway speeds that rises over 250 feet in less than a quarter of a mile
Diddy, I hadn't considered the implications of this hill. Assuming your facts are accurate, so 'less than ¼-mile' means 410 yards or 1240 feet, that is a gradient of (at least) 1 in 5. At motorway speeds? Really? Consumption must be pretty fierce ...
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Remapped diesels with increased levels of torque give an improvement in MPG, even large haulage companies aknowledge this.
www.tunit.co.uk/
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Remapped diesels with increased levels of torque give an improvement in MPG even large haulage companies aknowledge this.
that is 100% accurate. I've re-mapped my wife's diesel car and we're getting 3 - 4 ish mpg improvement, sometimes a bit more
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that is 100% accurate. I've re-mapped my wife's diesel car and we're getting 3 - 4 ish mpg improvement sometimes a bit more
I hope you have informed all relevant party's regarding that modification... Im sure the insurance company would need to know for a start - Id hate for the police to stop you............Ah - just remembered! ;-)
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Remapped diesels with increased levels of torque give an improvement in MPG even large haulage companies aknowledge this.
So why don't the vehicle manufacturers do it? There must be a disadvantage which you're conveniently ignoring.
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So why don't the vehicle manufacturers do it? There must be a disadvantage which you're conveniently ignoring.
Vehicle manufacturers have to meet whatever emissions regs that are in force world wide, they strap a car to a rolling road and collect all the exhaust gases in a huge bag. The vehicle manufacturers know the RR simulation exactly and lean off fuel mixtures at certain points in the rev range to enhance their figures giving 2 or 3 engineered flat spots in the rev range in every gear. This doesn't make the car more economical or make the car drive better in the real world.
Fuel qualities around the world also vary and car manufacturers also know the end user may not service the car to their specs and allow for this to in their OE maps.
Ask anyone with a remapped TD if the car is better / smoother / easier (less gear changes) to drive and if the fuel consumption has improved (providing the cars driven in the same manner as before) and the answer will be yes.
There will be some disadvantages if you drive the car like a hooligan all the time (clutch, DMF, tyre wear etc) but if you drive considerately there'd be hardly any more running costs if any.
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There was a long discussion about this here, a long time ago. In broad terms the best fuel consumption is obtained by driving with the engine at the rpm that gives max torque. Presumably as a diesel engine has a fairly flat torque curve (true?) it can give good fuel consumption over a wide rev range? I have started driving my 307 in 4th instead of 5th, when driving at 50 mph and I find the computer displayed fuel consumption unchanged.
Edited by Armitage Shanks {p} on 23/05/2009 at 10:47
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