My old 83 G20 with the 305 HO, 700r4 and 3.08s pulled down the best highway mileage with a tweaked quadrajet and recurved hei on it. The TBI and later TPI pulled down similar mileage numbers with better all around driveability and cleaner emissions. A properly tuned q-jet getting 21-23 mpg running 70 mph down the interstate set a high bench mark. With an out of the box edelbrock 1406 on a performer rpm intake it would only get 15 mpg. I was able to get the edelbrock up to a solid 19-20 mpg with jet/metering rod changes.
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