engine swap
 

just got givin a free wrx sti engine would this fit in my wrx? would I need to change anything?

if the engines are the same year, the block and internals should fit. the STI bottom end is stronger than the wrx because of forged componets. I'm not sure if the heads are the same or not though. I think all GC8 and GF8 blockas are all the same really but let someone else confirm
I would also suggest you use the sensors from your old engine as they may be different for an STI engine with an STI ECU.

Whole engine or bottom end... Might need mapping, I'm sure Scott or Simon will be able to answer that question

you need to define the exact ages of both the donor engine and your vehicle otherwise its all conjecture...........