CAI on our cars make a huge difference. Everyone on here has felt the difference. Now for the 335i and 135i turbos, the filters inside the engine bay is fine because the air from there has to go through the intercooler before reaching the engine, therefore cooling the intake charge. I see those cars all the time at the tracks with those set ups and doing way better than stock. Some even upgrade the intercoolers also for better cooling. As for the other engines, the best performance is when the filter is outside the engine bay, just like the Needswings or like my home made NealsWings CAI.