How big are the factory gas tanks in '73-'74 A bodies?

72bluNblu said

My factory manual lists the capacity at 16 gallons. Keep in mind that's probably off the dimensions, so you likely won't be able to use that much. There's usually around a gallon that you can't get out of the tank under normal usage. So I wouldn't figure on going more than 150 miles without a fill up.

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Back in the day, these tanks were notoriously difficult to fill because of the shape of the tank and the position of the filler. The optimum position of the car to fill is with the nose up and the body tilted away from the filler. The idea is to make the fuel filler the high point of the tank. Otherwise, an air bubble tends to fill at the rear of the tank. The air bubble tends to reduce the space available for fuel. When, and if, it gets displaced by fuel, watch out for geyser at the fuel tube.