I would have to agree there, anything over 40 and you'll start losing power not optimum.....in the winter my act's can drop to below 10 degrees if sat on the motorway for example and when they sit below 20 there is a marked improvement in the performance that i always notice anyway, car feels much sharper, snappier and pulls soo hard on boost! Get a biggen in there lol, if you think you really need it that is and as long as you're not blocking the rad of air?!