Why were the 260z and later 280zx intorduced with bonnet vents if the 240z did well (as far as I know there were no overheating problems with stock engines functioning properly) without them? Was it just for style or did L26 and onwards engines produce that much more heat than L24 (can hardly imagine why, but thought I would still ask)? Or was it only introduced for racing homologation purposes?

one word: vapour-lock

(ok, maybe its two words).