Reply #3: And now, a full-size sedan with a V6 or V8

[MineralMan]

gets around 25 mpg on the highway. That's true of my parents' big Ford Crown Vic.

I had a Lumina minivan, with a 3.6 liter V6, and it regularly did almost 30 mpg on the highway.

There's just no comparison between modern engines and those of the 1950s when it comes to efficiency.

Add to that the pollution those old engines spewed and there's no going back.

No question, though, if you put all the modern technology on those engines, they'd do a lot better than they used to. Basically, that's what's going on now. Add the catalytic converter, and you get rid of most of the rest of the pollutants. Other than that, though, the modern tech is what gets you both high efficiency and low pollution.

Now, if cars could be made lighter, that would help economy a lot. But, much of that weight is in safety equipment, and isn't going away.