I have a 1998 wrx impreza sti 2.0L turbo and want to put a newer engine in, will the 2007 ej25 just bolt straight in and if not what is the newest ej engine that will fit without to much modification?

trans will bolt up and engine will physically fit just fine on the engine crossmember.

 

bolt the 2.0 heads to the 2.5.

 

in the US market 1998's are Phase I and later are Phase II (with both being offered in 1999).  you'll need to determine if that's the case there as well.

 

same phase engines are easy to swap - but swapping across Phase I and II is far more challenging and most people avoid it.

it's my first time swapping an engine out what are the costs I'm looking at over all?

 

Phase I and II .

What's the difference between the phases and why is phase II harder?

Phase I is OBD2 but it was older electronics (sensors like MAFT, IAC, TPS, etc) Phase II is OBD2 as well with all updated stuff. I would look into if you are Phase 1 or 2 because I know the Subaru RS was a car that 98 was a change over year. Do some research and make sure that you know what your getting into. I had troubles just swapping a 98 to a 99 Outback and it was because I was running Phase 2 in the car but the 98 forester engine I picked up had sensors. for example the IAC was a big pain because it is mounted in a completely different spot on a phase 1 ej25 than it was on a phase 2 ej22. I had to make a adaptor plate up to get it to work with the new IAC. So my recommendation would be RESEARCH! find other people that have don't this and find out what their hiccups were. Its a lot easier to read about something that figured by someone else rather than doing everything yourself as you go. especially if this is your first engine swap.