I have an old 1979 Chrysler 300 that I keep around for fun. This is a massive car. it weighs 4,600 lbs. and has a large V8 engine, 4 barrel carburetor and dual exhausts. It gets roughly 28 miles to the gallon on the highway. My 1999 Dodge Ram 1500 has the same size engine (fuel injected) and is roughly the same weight, but only gets 21 miles to the gallon on the highway, maximum. My typical gas mileage on the truck ranges from 14 to 19 m.p.g. My 1995 Toyota Corolla gets 38 miles to the gallon with over 200,000 miles on the engine. I don't think the new Toyota Corolla gets that kind of gas mileage!
Now, there is a reason why many vehicles with larger engines get better gas mileage on the highway. The reason is that once a vehicle is up to speed, a larger engine doesn't have to work as hard to maintain speed. A small engine has to work harder. If you were to buy a full size pickup truck, you would probably not see a significant difference in the MPG between a V8 and a V6 due to the size of the vehicle. In fact, if you were to tow something, the V6 would probably use more gas than the V8.
Here's my problem: There has not been a significant across-the-board increase in fuel economy in at least 20 years. Why? Because the government hasn't made the manufacturers do it yet! The only reason they make the selection of small cars with the gas mileage they have is to comply with CAFE standards to offset the terrible gas mileage of their real market which has been trucks and SUVs. Of course a Toyota Corolla gets good gas mileage! It's a beer can fitted with roller skates! It should get 60 miles to the gallon! It is no huge feat of engineering to make a tiny clown car get "good" gas mileage. We know that gas mileage can be improved. The Honda Insight is capable of 115 MPG. Don't beleive me? Google it! I'm usually against the government getting involved in private industry, but maybe its time that the government forces the auto makers to substantially increase the mpg requirements on vehicles. And I don't mean let them have an easy way out of it. It isn't enough to simply cut back production on trucks and SUVs to slide under the CAFE requirements. The auto makers need to make all of their vehicles significantly more efficient.