Another link to official tech page from Subaru (FHI-Fuji Heavy Industries) about WRX and turbo for anyone else's reference,
http://www.subaruwest.com/PDF_files/Tech_PDF_Folder/june_2001_techtips.pdf
http://www.subaruwest.com/PDF_files/Tech_PDF_Folder/june_2001_techtips.pdf