A key to making more power on any turbocharged engine is the addition of a high performance air-to-air intercooler. This part in the simplest of terms, cools the air going from the turbo into your engine, much the same as a radiator cools the water inside the engine, by transferring the excess heat way using multiple passages through a core. A PERRIN intercooler fits easily to the front of your Subaru to maximize cooling.
Perrin's testing shows the optimum core design is the 3/8” bar and plate style that has a 3/8” charge air and ambient air path, instead of the common 1/4” size. The PERRIN bar and plate core design is much more durable than tube and fin with the ability to withstand rocks and other debris, which may enter the scoop.
This was done on a 08 WRX running Stage 2 with a PERRIN intake installed. Perrin did nothing but swap to the larger intercooler between runs. You can see on this that the freer flowing, more efficient intercooler makes about 10WHP more with no additional ECU tuning. With Stage 3 mapping you can expect to see about 10 more additional WHP!