79 L-48 with 3.55 gears and 350THM auto:
Average of about 14 mpg with the former Rochester Carb. Just upgraded with a GM performance parts manifold and Holley 4160 carb. New dual exhaust (nice chambered dueal kit from Midamerica). Much better throttle response, much stronger acceleration off the line - about the same at upper RPM. Gas guage seems to drop off a little slower, but hard to really tell as I seem to be on it frequently so I can enjoy the really crisp exhaust note.
Guess it will be awhile before I drive it to maximize mileage....I am guessing sometime around the year 2035.
In the end, we didn't buy these things for their outstanding economy.
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C3: 1979 Corvette Coupe, Auto, L-48, Red/Doeskin (my wife's fave);
C4s: 1986 C4 coupe (SCCA road race car), satin black, 4+3, Z51 package, L-98; & 1993 C4 coupe, white, 6-speed, LT-1.