If you built a truck with a V8 it can be made to function on 4,6 or8 cylinders at the drivers discreation. On a fuel injected motor you can, through electrical contolls, cut off the gas and spark to selected cylinders. Doing this would give the driver options to drive on 4 cylinder for greater gas mileage but if towing or hauling can choose to engage 6 or 8 cylinders depending on need and saving greatly in gas mileage