what engine,? they had a few different ones the used in those and it would help to know that, i checked and on avergae most of those cars got between 13 and 18 miles to the gallon,and that was with the 318 option as an engine,good luck.
That's probably fairly close. You can save lots of gas with a big V8 if you keep your foot out of it when accelerating. The gear ratio also has a lot to do with it on a muscle car because there is no overdrive. A Charger with low gears like 3.23's will save on gas but kiss that mileage goodbye with high gears like 4.10's.