W2A cores are huge!
the small ones are only good for 300hp or so
something like this
http://www.frozenboost.com/product_info.php?cPath=218&products_id=210&osCsid=e000b70a3e9fdd6bc4bb5d7e6537d46f
would be the bare minimum for a stock 25 imo. and you will never fit it where the side mount was.
Trust me I tried
you may be able to fit it where the stock airbox goes, but you will have no room for an air filter/ intake pipe
I also tried that