I plan on getting an 1967 ford f100 and saw that the gas mileage isn't the best on these trucks. The certain truck I have my eye on has a V8 5.8L engine and was wondering if more liters in the engine means better gas mileage? Or does liters have nothing to do with mileage?
On most vehicles, the larger the engine the more fuel it burns. The 5.8L size is the displacement (or swept volume) of all the cylinders (eight in your case) added up. When the cylinders fill with the air/fuel mixture, this mixture should be stoichiometric at about 14:1 ratio (no matter what kind of gas/petrol engine you run, this is basically what you are shooting for). This means that in order to fill the cylinder correctly, it takes more fuel per revolution of the crankshaft, which means more fuel at any given RPM. This equates to less MPG. The trade-off here is that you get more power/torque out of the mix.
NOTE: Please understand, what I've written above is a generality. There are engine combinations out there which get better mileage, but generally what I've written is accurate.