Most of the early WWII fighters had limited range. Lindy tinkered with the RPM’s used while not in combat the Lockheed fighters could get save 80 gallons per run.
You’d have to search the subject to get a coherent explanation with some detail.
I don’t think it was a matter of inventing any new equipment or gadgets...it was more about applying his long-distance experience to the aircraft in question and squeezing out better fuel economy.