[MARKDTN]

The only apples to apples compare I can give is my own. I have an '83 K20. I got it with 42k miles. It has a 700R4 and 3.42 gears. It always got 14ish in town and 17ish on the road. At about 150k a cam lobe went down. I pulled the engine complete and went to a '90 Corvette Tuned Port 350. Now my mileage is 17+ and town and over 20 on the road. Towing/loaded is noticeably better; with the Q-jet you were always on the gas at the slightest hill. Now just a slight touch and it pulls. That swap is nothing changed-stock manifolds, same transmission and gears. So 3 mpg better which is better than a 20% improvement. That is my experience, yours may vary.