This thread is to give a rough idea of a generic setup to suit a Holset install on a Subaru.   Notes:   Im running a set of bl/bp twinscroll headers/up pipe endorsed by murch. If you run the calcs on the header volumes theyre a better fit than the V8 STI ones. Smaller the better with Holsets.   You will need a twin scroll sump if you do not have one fitted.   An HX35 or the Murch HRC35/2 is a good fit for EJ20/25 to around 350wkw but bear in mind you need