Does anybody know why some Saab petrol-engined cars have noticeably lower emissions than their Vectra equivalents? Their diesels have very similar emissions to the diesel Vectras. Only ask because if the threshold for highest road tax goes back to say 200g/Km then my 2.0T with 214g/Km would get clobbered but the similar Saab Vector Sport 2.0t (same engine and 189 g/Km) wouldn't.