open block- cooling jackets completely around cylinders, open spaces.
closed block- solid area between cylinders, good for boost.
the ej20g is a good motor, but they all have been beaten to hell in japan and finding parts is difficult.
It's definitely possible to get 300+whp pretty easily, but the reliability factor will decrease with the increase of power. The EJ20G, first off, is open block like you said. Secondly, they're known for being somewhat problematic, internally speaking. I think you should go with a stronger block. Spend the time and money now in getting a closed block or an STI block and you'll worry less later about blowing it up. They're also easier to get parts for
and im guessing the only way to know if it s open or close is to take off the heads also is it possible to add the closed block or simi closed block after having the swap done say if i run a stand alone