In the B-17, each of the inboard nacelles contain the main landing gear and wheel (when retracted), a 37 gal. oil tank, big air induction system's intercoolers and ducting, the engines' accessories and engine. Each of the outboard nacelles contain the oil tank, the turbocharger, induction system's intercoolers and ducting, engine's accessories and engine. All of these require a large amount of volume and is mounted ahead of the front wing spar. There is not much "wasted" space.