Best mileage V8 I had was a ‘79-360/904/2.76 in a Dodge Magnum sporting 235/60/15’s on all 4 corners. I gave the engine dual exhaust off of the exhaust manifolds @ 2-1/4 w/an H pipe, a factory 4bbl w/a 600 AFB and a vacuum advance distributor from the junk yard off a truck that I just stabbed in and ran w/a Chrome box.
The reward was a solid 20 mpg’s up and down I-95 multiple times to and from NYC & ether Richmond Va. or Atlanta Ga.
17 mpg’s, and I got roasted big time here by every slant six guy (and a few others) for not knowing how to tune a 270,000 oil leaking, rocker clunking, dog leg driving ‘71 Scamp with a 225, rear gear unknown.