Installation Instructions for: Part Number 21-472 2002-2004 Subaru Impreza RS 2.5L 2003-2004 Subaru Impreza TS 2.5L 2003-2004 Subaru Outback Sport 2.5L.
The AEM Cold Air System is the result of extensive development on a wide variety of cars.
Each system is engineered for the particular application. The AEM Cold Air System differs from
all others in several ways. We take the inlet air from outside of the engine compartment where
the inlet air is considerably cooler than the hot under hood air. The cooler inlet air temperature
translates to more power during the combustion process because cool air is denser than warm
air. AEM has conducted extensive inlet air temperature studies and we have seen temperature
reductions of up to 50 degrees by pulling air from outside of the engine compartment. The air
mass flow to the engine is increased because of the increased airflow and reduced inlet
temperature, which translates to more power. The AEM Cold Air Systems come with complete
instructions for ease of installation.
Our system is constructed of lightweight aluminum and then painted with a zirconia based
powder coat for superior heat insulating characteristics. The aluminum will not crack in extended
use like plastic and it is actually lighter than plastic. The tube diameter and length are matched
for each engine to give power over a broad rpm range. Unlike the plastic systems that use a
continually diverging cross section, we take advantage of the acoustical energy in the duct to
promote cylinder filling during the intake valve-opening event.

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