Fuel economy = short duration, low lift cam and small carburetor. I have a Crower 267/271 cam in my 383 which is close to the stock 4 bbl cam which is good for performance but not for economy. Look at their Baja Beast or maybe the Mileage Compu-pro cam. 250ish duration (200 at .050),.420ish lift and 112 centerline. I would go with a 500 cfm 4bbl for the ultimate in mileage. When gas wasn't garbage, a friend of mine could get 20 mpg highway out of a 440 with that combination.