I am in the process of converting my 911SC from CIS to EFI. A couple of days ago I installed the ECU with all the sensors connected to it. The fuel injectors have not been installed yet.
Since the ECU has an air temperature sensor, I decided to take some air temperature readings in the engine bay while driving. All the readings were done on the same highway and all within about 10 minutes of each other.
The first reading was done with the sensor attached to the grill of the deck lid and then the decklid was closed.
While driving at about 120Kph for a couple of minutes the temperature read 80F (27C or 300K).
Next I attached the temperature sensor at the intake of the air box.
Again driving at the same speed, the air temp was 115F!! (46C or 319K). I could not believe the temperature had risen by 35F (19C). I repeated the experiment and got the same results. I also put the air temperature sensor in the air box and was still reading 115F.
The increase in temperature results in a 6% reduction in air density and thus a 6% loss of horsepower.
A cold air intake seems like a great idea here.