the theory behind the movie is that fuel is scarce so that would make sense to show the blower on/off when few people know what it is. viewers not in the know assume it's going to make more power. mostly theatrics.

a car like that at the time the movie was made wouldn't have had efi, so for it to even work would be in a roundabout way what crxgirl has alluded to...clutch driven pully for the blower and some alternate intake runner. regarding tuning such a carbed beast...good luck if economy, driveability, and power all wanted--it wouldn't happen. now w/ an efi system as long as the map is tuned for boost it wouldn't matter. blower off=not in boost portion. blower on=in boost map w/ fuel/timing adjustments.

realistic=no. a supercharged car can get great economy and power as long as it's tuned.