1967 Barracuda - Slant Six (orig) or 440 Big Block? Daily Driver, Need MPG

if you have to ask what the MPGs are then you probably need a newer econo-box.

Most normal people don't build these cars for economy.....I have a 72 swinger with a 440 and its a real fun car, I only fill it up with gas when its empty.

Unless you have the will power of a monk to stay off a 440 then maybe .....big maybe you can match the economy of a modern econo-box.....but more importantly, why torture yourself, just build it as a fun car and use a modern car for the econo commute.