So even a billion dollar company like VW had to build a special one off car and drive it very carfully to acheive good results.

The Lupo 3L TDI is the world's first-ever production-line 3 litre car, a milestone of energy conservation in automobile engineering. Volkswagen presented this ultra fuel-saving version for the first time at the automobile salon in Paris in 1998. Only 9 months later the champion fuel-saver was already on its way to the showrooms.

There are fine details of difference, both inside and outside between the normal Lupo and the three-litre Lupo. It is 150kg lighter because, in order to reduce fuel consumption, it had "to loose a bit of weight". The vehicle body is made of completely galvanized sheet steel. Aluminium was used both for the bonnet and for the doors. In addition, the tail gate consists of aluminium on the outside and magnesium on the inside. Even the heat absorbing glass is lighter. Rolling resistance is lessened by particularly light, narrow tyres which have been mounted on aluminium-forged light wheels.

Of vital importance is the engine: a brand-new three-cylinder Turbo-Diesel with 1.2litre cubic capacity, performance 45 KW or 61HP. Its highlight is the new pump- nozzle-system which produces an extremely high pressure for each individual cylinder . This enables a more efficient combustion of the fuel than in conventional diesel engines.

The result is impressive: a high torque i.e. a good thrust of force, even from low speeds and still an absolutely sensational consumption of 2.99 litres to 100 km. The maximum amount of fuel is saved when the 3-litre Lupo is driven in the so-called Eco-Mode. This means changing up gear early and changing down gear late, in other words, at the most suitable speed for saving energy. Our record-breaking drivers are naturally trying to drive very defensively and to even manage on 2.5 litres in this mode. They will be supported in these endeavours by Volkswagen's so called stop-start system. When standing for longer than 4 seconds a touch on the brake switches the engine off. It starts up again when the brake pedal is released.

Although as regards fuel consumption the Lupo is absolutely unique, our record-breaking team is nevertheless facing an enormous challenge. It is no small task to be on the road for 80 days in all kinds of countries under hard climatic conditions and coping with some extremely bad roads and driving conditions and still keep to the prescribed speed.

The examples you have given are not real world cars, in real world conditions, driven by real world people, in everyday life.
So like I said, It's back to the drawing board.
There is no 100mpg carb.and if you are going to increase fuel consumption thermal efficiency is another place to look.
Just ask VW.

I think rookie missed this article where VW drove the 3L Lupo around for a while, and got pretty darn close to 100mpg@55mph average speed.
Or this one.
That being said, I don't think we'll see one any time soon, even if costs go down, since most people are more than happy to pay out the wallet to have a "big" vehicle. It's there, but it'll be a while before a decent production run imo.

Why isn't it a 100mpg EFI system, seeing how Efi's generally get much better mpg?

Because that's folklore, the 100 mpg carb :p
Makes for good story telling thou.

Back the summer I think it was "Mazda"? I read an artical in Hot rod magazine about there directed injected gasoline engine. It runs on a 60 to 1 air fuel ratio. 100 mpg, no problem.

Also, because this story is an old one. Stories about 100MPG carbs predate EFI by YEARS.