Fuel consumption: Old v New

[Matra et Alpine]

In the 70s had a twin cam Escort which with the best will in the world delivered 25mpg and when "driven hard" 10mpg and when comepted about 7
Now have an RX-8 which with the best will in the world delivers 25mpg and when "driven hard" 18mpg and when competed about 18mpg. So I call that improvement
Rotary the worst example perhaps
But the difference in fuel consumption for equal performance is huge in piston engines due to better fuellling, air/fule mix and spark as well as advanced timing.

But, I came to comment mroe on the relative merits of the weight gain.
Yes, I hate the weight gain for waht it does to performance and fuel consumption.
BUT the advantage for the vast majority it brings in less death and serious injury is a reaonable balance in the equation. ( Just wish when they did "Performance" versions they'd let us make that risk choice and get somethgin REALLY light )

[MilesR]

Thank you fellows. It is nice to be appreciated.

Ferrer, I was using the 1966 Holden as one extreme, and to illustrate the recent trend in new car sizes and weights.

Badsight, when I referred to the speed of modern cars, I was referring more generally (and should have said so) to what I see as a trend of accelerating faster in new cars than in old ones. When I am driving an older car, I do not tend to push it harder than is necessary. I find that acceleration can tend to happen quite a lot more slowly than the traffic around me. The combination of a wider, flatter torque band, and much lower noise levels, even under high load, make it easier to drive a newer car much faster, without seeming to push it any harder. For this reason, I am sure that the majority of people drive new cars faster than they would have driven older cars, probably without noticing. I also think that it is easier to exceed the speed limit in new cars, for the same reasons. I think that the disagreement between manufacturer's claims and real-world measurements is partly due to the acceptance of this extra speed as normal.

Also, on a minor technical point, I think that there is a little misunderstanding of the term "efficiency". Efficiency is the percentage of chemical energy from the petrol that ultimately is translated to the kinetic energy of the car. If a car is driven at a speed below its ideal cruise speed (which should be in its engine's peak efficiency range), it is true that the engine efficiency will be below its peak. However, at a lower speed, the car will have a lower kinetic energy, and so will need less energy to bring the weight of the car up to that speed. It will also be overcoming significantly less aerodynamic drag, and thus the engine will need to generate less power. This lower power requirement will normally easily overcome the lower efficiency, and therefore the fuel consumption at lower speeds will almost always be lower than at high speeds. This may cease to be true in extreme cases, where the engine is running so slowly that it is labouring, or burning fuel without generating significant power, but for realistic comparisons, such as 80km/h and 100km/h, this is normally true.

[Matra et Alpine]

It's the delta in the kinetic energy that is important in bringing the car up to speed.
other than that nice write up of your views.

[crisis]

I can only agree. A 1980 350 Chev gave around 14mpg compared to a LS1 350 at around 20. And when you consider the increase in power of the newer motor it is even more impressive.

[Badsight]

but for realistic comparisons, such as 80km/h and 100km/h, this is normally true.

well your opinion of whats happening with a cars fuel efficiency isnt translated to reality, most modern cars do not have 80 km/h as being the more fuel effiecent speed. cars involved with this kind of testing these days generally show 95 - 105 as being it

as for manufacturer fuel consumption rates - well they seem to over-estimate. i dont know why but being able to beat quoted manufacturer consumption figures isnt a new phenomenon

you would think they would try to get the best figure possible for marketing reasons

[Badsight]

That's a part of it too, but the point still stands. Remember with the F1 that the engine was outsourced to BMW, and given the press that BMW got out of that, I'm sure there some cost savings for McLaren with that situation. That along with the no compromise approach with the gold lined engine bay and whatnot point to a no holds barred approach to the project. The MP4-12C (such a bad name..) doesn't seem to have had quite the same hard core approach.

"hard core" ? the MP4C has a higher degree of complexity to it than the F1. more compromised for comfort sure - but not lower tech/developed. actually ride comfort can take extensive testing to sort

the Gold Leaf isnt the huge cost you may be thinking it is - rather the use of iconel compared to ordinary stainless in the MP4 is much better example of higher cost materials

& the out-sourcing of the engine ? compared to in-house development it should run the opposite way in lowering the F1's cost compared to the MP4

sorry but it was the low run & desire to make the project profitable (small company - lenghty RnD) is what made the F1 cost so much. these days Mclaren is bigger, more adept at getting a car for the road developed & with 1000/year the unit cost is much lower

[Matra et Alpine]

B, what source do you have for the gearing now having the engine efficiency point being at a higher speed ?

Not seen any research or studies suggesting that and many still hang on to the 50-55mph as being "most suitable" for fuel efficiency. THough you find few real studies on the validity of that too

[Ferrer]

Now have an RX-8 which with the best will in the world delivers 25mpg and when "driven hard" 18mpg and when competed about 18mpg. So I call that improvement

Either you drive very fast on open roads or very slowly while racing.

15,7l/100km while racing? Surely you must come last everytime there's race...

[Matra et Alpine]

Not entirely, Ferrer, it's a consequence of the way a rotary works.
The difference between normal fast driving and competition is NOT as big a difference as with a piston engine
I'm talking stock fuelling here .... but yes the rev limiter "beep" warnign comes on every drive
Came second at last sprint event - both days Given first was a judd-race-engined Rover I wasn't upset

[clutch-monkey]

not bad, would be hard pressed to get that out of the older turbo which has roughly similar power..

[VOGUE_MAN]

I was massively surprised when the MY2011 X5 was released to see that the diesel version dropped from being over 10L/100km to under 8L/100km overnight. This was not on a new model, different engine, weight ect... it was simply that every year people want to see consumption figures drop and 2010/2011 saw BMW have a bigger hurdle to jump due to VW, Audi consumption figures also dropping dramatically.

My thoughts on this, I can't even imagine how low consumption figures could be if manufacturers were actually trying 100% to provide the lowest number possible and wasn't withholding technology to suit their future sales needs.

[clutch-monkey]

there are people on ausmini experimenting with putting the 1.5L petrol engine out the jazz, and the 1.6JTD engine out of fiat (?) into original mini's. interested in their fuel economy results. wonder if lightweight wins out over modern aero

[Matra et Alpine]

Or maybe just tune the old engine properly.
The 80s "E" editions were published at 60mpg at 55 mph

Most engine transplants in to old minis here are for power/competition.
Everything from Honda VTEC to bike engines Including a 5litre V8 -- got pics somewhere, made for an "interesting" driving position

[Badsight]

its interesting that the new Jazz 1300 makes 100 Hp - the same as the injected D13 from 1988 that was fitted to the 800 kg Honda City (has 15 NM more tho)

the 850 mini was a genuine british 60 MPG IIRC

[Matra et Alpine]

Only if in perfect tune, new plugs, filter, carb setup properly and contacts adjusted, on a good day and skinny tyres, B
Gearbox ratios (and number) weren't too helpful later diffs on the 998s improved things..
The 850 average was a solid 40 mpg tho'