closed chamber 714 casting 318 heads

If you maximize the tune, (Key words just spoken) the higher compression and higher octane fuel should out power and out mileage the low octane build. The cost offset should be favorable.

I do not see a problem getting into the 20mpg range. I did it in a '79 Magnum with a stock low comp. 360 & bolt on parts, no headers or cam change. 904 trans and 2.76 gears. 26 inch tire.