The last version of the "3.8," before the engine was called a "3800," came in at least 2 flavors: Ordinary and Legendary.
There was a 3.8 variant that got unspeakably high gas mileage. These cars were coveted by taxi companies. My friend who owns a taxi company bought his first one unknowing of any of this. The first day they put it in service, at the end of the day, the driver says, "It runs good but the gas gauge is broke." It barely moved after about 1/2 days use as a taxi. They got over 25-28 mpg in city use.
I even remember a road test of a GN or GNX where they were driving to the strip with the 5th wheel on and running and they were getting 44 mpg on the highway. I suspect this Mystery 3.8 might even appear in the turbo cars too. (Or will all turbo Buicks get 44 mpg on a level highway?)
We never figured out which 3.8's got the mileage. It was probably something like has to have the "brown" injectors instead of the "blue." And maybe a few more things.
Does anyone remember this or has identified that amazing variant?