318 MAX fuel economy builds?

My 76 charger with a 318, 2.45 rear, and 360 2 barrel Holley carburetor was good for 23. As is my current 78 fury 2 door (also 318) dead stock 2 barrel motor tht actually still has working lean burn... Only deviation from stone stock is true dual exhaust 2-1/2 all the way to the back bumper
That one has 2.76 in the rear end. No lockup in either one, charger was 727 fury has 904.