Best possible mileage?

That was a very non stock 170 in an aerodynamic 64 barracuda, 4 speed O/D cruising in the upper midwest with a vacuum gauge. Nothing like a pickup. Nothing like a stock 225.
I remember the National competition when all the auto makers got into the mileage challenge. 318’w we’re not used. The mighty /6 was and the 170 was the champ.