Under the bonnet is August but in the Sahara at mid day!
A while back I did some crude measuring of air temps.
OBD unit measured incoming air temp, 15deg ambient and OBD reading 35deg and still rising.
The surface of the polished filter box was reading 50deg on the surface with a thermometer.
The “ rule of thumb” is 1bhp extra for every 7deg lowering of air temperature.
I might actually get on with further attempts to get cooler air. I have taken the bonnet extenders off for the winter though.
Many moons ago when I was experimenting with my air filters I measured (admittedly not scientifically) air temperatures going into the AFM through the standard filter and trumpet and then through the K&N filter without the trumpet but open in the bay as 134fxd has done. I didn't measure airflow but I'm sure the flow increased without the trumpet as did the the temperature of the air going in by over 20 degrees, so I was just feeding more hotter air into the engine. Which is why I eventually rigged up my crude looking but quite effective airflow from outside the engine bay, this reduced the temperature going into the AFM by almost 40 degrees from the Trumpet temperatures with ambient temperatures at 27-32C. My reasoning was that the trumpet although restrictive in airflow terms is able to pull slightly cooler air from the side and through the louvres, whereas the open filter in the center of the engine bay just pulls hot air directly from the bay and exhaust below it. In the trumpet and open filter cases the engine works just fine with no appreciable difference to performance but I did notice a bump in power and acceleration with the outside airflow.
