All this talk about ducting to the radiator and oil cooler is spot-on. I used to race a '79 RX7, and I removed the stock grill and put some chicken wire in front of the radiator for rock protection. The car ran much hotter, so I put the grill back in (leaving the chicken wire in) and the temps went right back down.
The temps would still get pretty hot on a warm day, so I used foam to seal all the gaps around the radiator and oil cooler. At the end of a half-hour race the difference was almost 10 degrees cooler.
