it all depends on how u drive. if u have extractors, there're meant to improve fuel efficiency cos u have less back-pressure and ur engine dosent hav to work as hard to push it all out ur exhaust, but thats if u drive sensibily.
Same with manuals, they dont drink as much as an auto if u drive em nicely. Not too sure why but i think its cos of the torque convertors in autos that make em drink more.
i got a VS II S-PAK Manual with extractors and 2.5" Redback Exhaust and if i dont thrash it i get bout 400-450kms out of a full tank, but i cant help putting my foot to the floor and droppin the clutch.
<<<<!!!!!I LOVE MY MANUAL COMMODORE!!!!>>>>>>