Fuel consumption - where did it all go wrong?
Discussion
Monday night and Ed from Wheeler Dealers is rebuilding a 1977 Honda Civic CVCC. We had one of those back in the day and it boasted around 40 - 45 mpg. The early 80's Austin Metro was not that different and I seem to recall the Mk2 Fiesta could quote a figure of close to 50mpg with the right little engine. Through the 80's, 90's and the first half of the 00's MPG figures for new cars barely seemed to change however.
One might have expected, if not stellar improvement over time, certainly a steady improvement pushing us towards 60 and perhaps 70 MPG. Especially as during this time fuel consumption figures were clearly of importance given their visibility in advertising...some cars even quoted drag coeficient figures which were meant to help fuel efficiency. 'Concept' cars often featured supposedly higher efficiency figures.
It hasn't been until relatively recently that the MPG figures have shot up, what with higher efficiency engines, and hybrid power.
My question I guess is why did we not see any real improvement, given a seemingly clear desire from the consumer to get more miles to a tank? It can't just be the availability of fuel, as its cost has steadily risen over the decades (much of it tax I accept).
One might have expected, if not stellar improvement over time, certainly a steady improvement pushing us towards 60 and perhaps 70 MPG. Especially as during this time fuel consumption figures were clearly of importance given their visibility in advertising...some cars even quoted drag coeficient figures which were meant to help fuel efficiency. 'Concept' cars often featured supposedly higher efficiency figures.
It hasn't been until relatively recently that the MPG figures have shot up, what with higher efficiency engines, and hybrid power.
My question I guess is why did we not see any real improvement, given a seemingly clear desire from the consumer to get more miles to a tank? It can't just be the availability of fuel, as its cost has steadily risen over the decades (much of it tax I accept).
Edited by paulyv on Monday 23 May 23:36
Vehicle weight, size and emmisions.
How heavy was that 1970's fiesta? 900kgs? now one would be 1300kgs.
Engines burn a lot more fuel now because they can do that with lower co2 etc.
oh and power too. who would be happy with 40bhp now?
That Austin metro weighs 760kgs, and started with a 39hp 1 litre engine.
Current fiesta is 1100kgs and with its 1litre eco boost makes 100 -120bhp but is hobbled by current emmisions rules. Could be a Lot more efficient. But to match the metro you could lob off half the displacement.
How heavy was that 1970's fiesta? 900kgs? now one would be 1300kgs.
Engines burn a lot more fuel now because they can do that with lower co2 etc.
oh and power too. who would be happy with 40bhp now?
That Austin metro weighs 760kgs, and started with a 39hp 1 litre engine.
Current fiesta is 1100kgs and with its 1litre eco boost makes 100 -120bhp but is hobbled by current emmisions rules. Could be a Lot more efficient. But to match the metro you could lob off half the displacement.
Edited by RobDickinson on Monday 23 May 23:58
I think the obsession with CO2 emissions and BIK spelled the death of development of petrol engines because it was easier to meet those misguided targets with a diesel (VAG may be able to explain in greater detail)! 
Saying that I have a 2002 BMW 325ti Compact and the OBC is showing 34.4 mpg, which is way better than my MKII Escort RS2000 or 2.8 Injection Capri ever did and it is in a different league to them in performance so maybe progress has gone under the radar!
Saying that I have a 2002 BMW 325ti Compact and the OBC is showing 34.4 mpg, which is way better than my MKII Escort RS2000 or 2.8 Injection Capri ever did and it is in a different league to them in performance so maybe progress has gone under the radar!
I think for many people if you can get 35+ mpg then they'll be fairly pleased.
If your buying a new car on the basis of the claimed MPG figures in the brochure your going to be left very disappointed. Unless you drive around with a feather light foot at a constant 30 and all the panel gaps taped up.
If your buying a new car on the basis of the claimed MPG figures in the brochure your going to be left very disappointed. Unless you drive around with a feather light foot at a constant 30 and all the panel gaps taped up.
Car weight is a huge issue, for every advancement made by efficiency there was a negative effect (to economy) bought on by safety measures increasing the weight, the mk1 Golf is 810kg and a mk7 is 400kgs heavier.
It seems to have gotten slightly better recently though, the mk7 golf is lighter than the one before and the same for the current WRX STI.
It seems to have gotten slightly better recently though, the mk7 golf is lighter than the one before and the same for the current WRX STI.
2 main factors:
Performance and emissions. (and NOT mass as you might think, which is only loosely coupled to ultimate economy)
Performance:
An old metro wielded about 50bhp with all the finesse of a middle african dictatorship, a modern supermini has at least double that, and it's totally useable at low rpm. People accelerate faster now than they have ever done, it's just modern cars are so easy to drive they don't notice. In the search of grip, and interior space, cars have got a lot bigger (larger frontal area) and have much fatter tyres (what tyre size did a metro run again??? ;-) ) so rolling drag is higher. On the flip side modern cars are a lot more efficient, so don't waste fuel like we used to (accurate injection, higher CRs, better aero, downspeeded engines, low consumption accesories(EPAS etc) etc)
Emissions:
Being "clean" has fuel economy penalties. You have to run at lambda 1 (rather than being able to run lean) and additional strategies such as Nox traps, DPF's etc all take fuel to maintain. Catalytic convertors also strangle engine outputs, and reduce efficiency from their extra back pressure.
Finally, whilst old cars could get reasonable economy, a lot of the time they didn't. Falling out of tune, and running badly they used their fuel badly!
Performance and emissions. (and NOT mass as you might think, which is only loosely coupled to ultimate economy)
Performance:
An old metro wielded about 50bhp with all the finesse of a middle african dictatorship, a modern supermini has at least double that, and it's totally useable at low rpm. People accelerate faster now than they have ever done, it's just modern cars are so easy to drive they don't notice. In the search of grip, and interior space, cars have got a lot bigger (larger frontal area) and have much fatter tyres (what tyre size did a metro run again??? ;-) ) so rolling drag is higher. On the flip side modern cars are a lot more efficient, so don't waste fuel like we used to (accurate injection, higher CRs, better aero, downspeeded engines, low consumption accesories(EPAS etc) etc)
Emissions:
Being "clean" has fuel economy penalties. You have to run at lambda 1 (rather than being able to run lean) and additional strategies such as Nox traps, DPF's etc all take fuel to maintain. Catalytic convertors also strangle engine outputs, and reduce efficiency from their extra back pressure.
Finally, whilst old cars could get reasonable economy, a lot of the time they didn't. Falling out of tune, and running badly they used their fuel badly!
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