there is a lot that goes along with it
it is a good idea for the power but can be hard on the wallet
sti block weak spot is the pistons..
the wrx heads are fine but the cams are not close to the sti cams
so you need a more aggressive cams setup to even make sti power
the compression is the next issue you can do one of three things to lower the compression
1. thicker head gasket not the best way to do it
2. custom pistons better but not best
3. machine the heads for proper compression and it also removes any hot spots
from what I have heard from big named engine builders a few out there are not lowering the compression on crazy builds the real aggressive cams take care of any high compression issues because of the overlap
there are a lot of big hp hybrid builds out there with just a thick head gasket but it can be a gamble
you will need at least a vf39 to keep up with the 2.5... a 20g or dom 3 would be a great turbo for a mild cam hybrid
if you go any bigger than a vf39 you need 700 to 800+cc injectors and a bigger fuel pump
here read up
http://forums.nasioc.com/forums/show....php?t=1431376
Trying doing a little digging in the "Built Motor Discussion" forum:
http://forums.nasioc.com/forums/show....php?t=1085359
http://forums.nasioc.com/forums/showthread.php?t=903873
http://forums.nasioc.com/forums/show....php?t=1942615
http://forums.nasioc.com/forums/show....php?t=1356918
http://forums.nasioc.com/forums/show....php?t=2002598
http://forums.nasioc.com/forums/show....php?t=1038227
http://forums.nasioc.com/forums/show....php?t=1082001