does anyone know the compatabilities between head and block? i want to leave my EJ18 heads, and put in a Phase 1 EJ25 block. will this work, or no?

All EJ shortblocks will "bolt up" to any EJ head. So basically, yes, it will bolt up, however the combustion chamber will be badly shapped and the compression of the motor might be fubared.

You do know the EJ18 heads are horrible right? Totally suck... IE not good.

For a little reference, here is my little experiment trying to fit EJ20 heads onto a EJ18 block:

http://community.webshots.com/album/110209915vXVzdU

will that work?

Will what work? The EJ20 heads on an EJ18 block? Yes, but you need custom 1.8 pistons, otherwise the EJ20 valves will hit the piston. You also need a bit of wiring work to get it to run.

damn. maybe ill just swap in a 2.5 and let the 1.8 ecu run it

Thats what im doing ;)