Originally Posted by Mike Rainbird

Over the quarter it also makes a HUGE difference. As I said, the recovery rate takes at least 15 - 30s to get back down to ambient temps, and although the actual air going into the engine is actually cooler than this (because the turbo is flowing HUGE amounts), the ECU doesn't know this, as it is going by what the ACT sensor says it is, so you want as cool air as possible going into the engine to speed up the recovery rate of the sensor (which can see in excess of 80°C from heat soak in stationary / slow moving traffic).