As boost pressure is increased, the temperature of the inlet air increases and robs power from the engine. Substantially revised for 2003, the APS dual entry top mount intercooler with twin induction to better spread the cooling effect on the incoming charge is designed for maximum street performance on any MY01 onwards WRX. With the significantly lower pressure drop (less than 0.02 Bar / 0.3 psi at 240 kW / 320 hp across the intercooler and 1.6 psi total pressure drop including the throttle body), it's a perfect partner for a high output roller bearing turbocharger.

For optimum performance, the intercooler core itself is internally finned with large internal charge air channels. This results in huge cooling capacitywith very high contact area for heat transfer and the highest volumetric air flowrate. Just as importantly, the APS cast alloy end tanks ensure even charge air distribution through the intercooler core without "hot spots" commonly found in aftermarket intercoolers. That along with a huge 11,075 cm3 (677 in3) of intercooler core volume compared to the standard intercooler's 4,305 cm3 ensures the maximum possible intercooling performance.

At nearly 2.6 times the volume of the standard intercooler, the APS top mount intercooler is absolutely the largest top mount intercooler that is possible to practically install in the late model WRX or STI - with core dimensions of 51 cm x 19 cm x 11.43 cm (20.07" x 7.5" x 4.5").