Some teams, probably McLaren, Red-Bull, Renault and Mercedes have to modify their actual diffusor. I assume the problem is related to the bog holes above this element. What kind of an effect can it have to the performance?
ps: It was interesting to see Ferrari have only a small hole at the back of the engine cover while teams mentione above have a really monster hole.

http://forums.autosport.com/index.php?showtopic=126050

Indeed.

A reminder to all members to use the search function before starting new threads.