It's not necessarily hard to build fuel mileage. As long your expectation are in check. Plus there's 2 types of mileage in town and highway. Everyone seems more concerned or talks more about highway.
Highway is fairly easy to obtain just add OD.
Even modern cars similar to our cars can't break 20 mpg in town.
We all know the benefits of larger cubic inch
But it's not a free lunch everything comes with trade offs.
Compare 340 vs 416
Both can make the same power say 450 hp.
Torque both are gonna make about 1.2 lbs-ft which equals out to 408 lbs-ft and 500 lbs-ft.
A 340 with 3.91 gears will equal the torque to the ground of 416 with 3.23 gears. And both engines will pump the same cfm at the same speed. Similar mpg.
So both would have similar performance and mileage but the 416 would be considered more steerable.
Sure you could put the same gears in both but the 340 will gain mpg but lose performance compared to 416.
Obviously this is generalized.
