The 318 magnum is superior in many areas. Better heads, more efficient chambers, smaller lighter valves, and a roller cam...all those things will help mileage. I have a stone stock junkyard 5.2 in a dart, with a dual plane intake, thermoquad, and a set of Doug's headers, 904 and a 3:23 rear. It gets 21 mpg on the highway easy peasy. No tricks
