BMW 330ci fuel economy - how is it possible?

Alright then, I won't mention food, much as I love good food.

It seems as if you seek to detract from a what a manufacturer is achieving, when it exceeds what others are achieveing, by pointing out that: "the only difference is that they have actually done it and the others haven't yet, it's not that the others can't/won't".

Do you dislike a more rapid pace of innovation?

I have no wish to detract BMW because they are very good. However what I want to point out is that there is far more to the business of engine & vehicle engineering than a bunch of reported figures in a magazine or even those reported than the government. Also that there is a consequence and compromise associated with every decision made in engineering.

Perhaps I have a blasé attitude to some of these "innovations" because I'm surrounded by it every day (I work for a large independent engine consultancy that at one time or another has done work for everybody). I'm certainly not against innovation because it keeps me in a job, but I like clever and simple solutions that extract the most bang for buck! And sometimes it means holding back slightly, asking questions and finding out what's really going on.

As someone already pointed out, the resistance offered by the dyno is calibrated to the actual resistance vs speed curve of the car, measured by coasting down in neutral.

You don't need to separate the effects of weight and aerodynamics, you know what the car weighs, if you know m and a you can calculate f, and f is all you need.

Ah, I didn't spot that bit. So they must measure the coast-down on the road, right? Then calibrate the dyno resistance to that?

http://www.bmw.co.uk/bmwuk/pricesandspecifications/0,,1156___bs-Mw%3D%3D%40bb-TEkwOA%3D%3D%40sit-bmwuk,00.html

Just seen on here the combined figs and are as follows;-

318i 47.9mpg I4 Power 143bhp
320i 46.3mpg I6 Power 170bhp
325i 39.8mpg I6 Power 218bhp
330i 39.2mpg I6 Power 272bhp
335i 31.0mpg I6 Power 306bhp

Stand corrected - when did BMW drop the 2.0ltr I6?

That's a useful table and confirms the pure comedy of these "official" figures. In the real world the mpg performance of the cars will produce a much narrower range, slanted towards the lower end.

Our old friends the laws of physics dictate that as each car weighs more or less the same and offers similar wind resistance it will take about the same amount of energy to accelerate any of them and keep them cruising. Hence similar mpg, give or take a bit of heat and pumping.

I agree that the regeneraton of the nox cats is no free lunch but the benefits out weigh the penaly imho.
The regeneration strategy used on the bmw requires the engine to run at lambda 0.9 during this process now bear in mind that these engines run at lambda 2.5 when in stratified/lean burn mode means that the gains are worth pursueing. The regeneration process does not have to wait until the cat is full and it can be done under hard accellertion when the fuel mixture is rich anyway so the effects of this process are minimised.It can just keep regenerating bit by bit as it goes along it does not have to do it all in one go.
It will be intresting to see what the other manufacturers do to hit the eu5 limits.

Even in the E46, the 320i was a 2.2 I6. The 318i was a 2.0 I4. The last 2.0 I6 was in the E36 320i/early E39 520i.

In 2002 I had an E46 318i automatic for 2 weeks. Drove it down to Sussex and back round the M25 and on A-roads, averaged 39mpg driving economically but not too slowly. With diesel currently being 15%+ more expensive than petrol, you'd have to manage 45mpg to beat a 6yr old petrol car with an auto box, on which the only clever economy measure was Valvetronic (actually, pretty f---ing clever so that's probably a bit demeaning). With a decoupled alternator, direct injection etc, I see no reason why 50mpg isn't feasible; fuel use is down to the weight of the car and powertrain losses as well as engine efficiency on part throttle. DI has improved part-throttle efficiency immensely, as did Valvetronic, so in similar use a small-engined 3-series will use a similar amount of fuel to a bigger engined one. All good, until you can't resist exercising your right foot

BTW, I was surprised to see over 40mpg from my E39 540iA Touring today. I accidentally reset the fuel computer rather than average speed reading on the M40, and at my destination discovered how efficient I'd been

No, 10% more. It doesn't take a genius to work out that if diesel is 10% more expensive than petrol, then you need to be getting 10% more mpg to break even.