318 MAX fuel economy builds?

there are a whole lot great suggestions and ideas here and I think that you need to decide if you just want to plus a few miles on the ticket of your current set up or if you're looking to build something to wring out every last drop of mileage.

273 makes a note of what the ROI is on mods while looking for that mileage and that's something that you should have in the back of your mind.

giving your current motor a mileage master glow up with a few bits and bobs won't break the bank; but building out a full blow motor would ultimately negate any savings in fuel mileage you'd come up on.