Miles/gallon: Newer vs Older Cars

It's all horse snot. New cars weigh more than old cars due to impact protection regulations. Fuel injection was developed initially for fuel economy.
And......a gallon of gasoline is only capable of delivering a certain amount of power, usually measured in BTU. This can be converted to horsepower. No matter what! A good running older car or a brand new car matters very little. The only way to get better mileage is to get a smaller less powerful car.
This also debunks the myth of the 100mpg carburetor that got so many people killed and/or paid off.