Good gas mileage in a heavy vehicle is difficult to achieve. Modern v8 1500 series pickups are generally still at or below 25 mpg. My SRT charger barely got 25 mpg highway. That being said, there are ways of eeking out better mileage with any car, without tearing into it too deep. Starting with the engine, getting the most efficient burn is key. As stated earlier in the thread, tuning is everything. The carb must be working optimally for the requirements of the engine. If you are using a Holley and have low engine vacuum you may need to change the power valve to better match the low vacuum signal. The factory power valve needs a good bit of vacuum, something like 12 inches at cruise to stay closed. Otherwise it will be adding fuel to the mix that is not needed. The ignition timing must be right, the spark plugs must be the right range and gap. The ignition system as a whole must be working optimally, good wires, coil & distributer. A clean & free flowing air filter will help, a lot of efficiency can be lost here. Free flowing exhaust will help. You dont necessarily need headers and flowmasters (though they sound cool too) but a clogged exhaust is bad news. Having the right weight oil in the engine will help, go with the thinnest oil possible that does not increase consumption. You must also use the proper gas for the engine. Just because you aren't running a 11:1 race motor doesnt mean you cant benefit from higher octane gas. Carbon build up can cause detonation which is bad all around. You must have the proper air pressure in the tires, mileage is lost from increased drag here. Even things like a 'loose' torque convertor can rob some mileage. Check the brakes as well, even slightly dragging brakes will hurt mileage. Lastly, driving style. It amazes me how many people are on and off the gas unnecessarily while just cruising along. Every time you push the go pedal the accelerator pump in the carb blasts more gas down the manifold. A steady cruise will gain some mileage versus on & off the gas. You probably aren't going to be in the 25 mpg range but making sure everything is tuned correctly could be the difference between 11 mpg and 16 mpg.
Hope this helps!
