Originally Posted by dssilvestri
Did anyone notice the vent from behind the grill leading to the airbox on their hemi ? what exactly is this ?
It's the combustion air intake. As stated previously, because it takes air in front of the radiator support, the air temperature tends to be somewhat cooler than if it were pulled from the engine compartment (like older cars).
My IAT tends to run in the vicinity of 10-20F above ambient, depending on ambient temperature, vehicle speed, and whether or not MDS is active.
The denser air contains more oxygen per unit volume, and thus, the engine can can produce more power per ignition cycle. PCM uses IAT and MAP sensors to determine incoming air density and then calculate appropriate fuel charge delivered by the fuel injectors.
Jeep did it right with a compromise design to get coolest air, while still protecting against unwanted debris intrusion into the air filter cavity and a high location that minimizes the chance of accidental water ingestion. Since it is sized to flow enough air to reach red-line full power (maximum air flow), it will have more-than sufficient air flow for normal driving (1,500-3,000 rpm) conditions.
Factory has already given you a CAI!