No it isnt. The STi motor is a closed deck and has Dohc (if you can call them take) as opposed to the SOHC the 2.5rs has. The Sti motor has an 8.0:1 compression while the 2.5rs has a 10.0:1. It def cant handle boost as well as the Sti motor can. You'd be lucky to get 9psi from that block, stock of course. It would be a much wiser investment (cheaper too) to swap in the ej20 motor. Also, the transmission on the 2.5rs is actually from a 1.8 Liberty, it cant handle big horsepower either.