Yes, they
have to get disassembled. A lot of people have asked that, actually... is there a particular reason it gets asked?
I'm not sure it's quite understood what is involved in disassembling a turbo for this purpose. The cartridge is left completely untouched. The housings simply slide off of the cartridge and it's EXTREMELY simple to do. It's not a delicate or complicated procedure and doesn't involve special tools or anything. There's one 10mm nut that holds a v-band clamp on the exhaust housing.... loosen that and the housing literally just pops off. The compressor side is different on a lot of turbos but it's either like 6 small little bolts that hold it on (take the bolts off and the housing just slides off) or it's a large snap ring. The important part, the cartridge, doesn't get tampered with in any way
.
...and on top of the simplicity with which the housings come off, all of the OEM Subaru turbo housings have a mark or a 'pin' (and a hole on the cartridge) on them so they line up perfectly when they're reinstalled. On turbos like Garrets, we make an indexing mark or use a reference on the turbo to make sure they line up properly when assembled.
Make sense? The hard part is in porting
properly so efficiency is truly increased, not reduced.
Jeremy