Yep, used to take it for granted, but I just did a search now, and found out thats not normal on scoobs (What the f##¤ ). Not shure how its done, but Im shure planing on finding out. No 2.5s where stock with the closed deck right?

 

There is no factory closed deck 2.5 block to my knowledge.

The STi has a semi closed deck EJ257 block but as Tony says, it has limitations.

 

2.5 Subaru engine are weak,you can have look here https://www.scoobynet.com/scoobynet-...-failures.html

I will recommend little bit invest to make your engine stronger...
And about the AFR look at this thread(is not subaru related,but related to Subaru tune) http://www.eng-tips.com/viewthread.c...=101915&page=5