89 ES ------>2.5L Turbo I (most likely)

That means it is a non intercooled, "Common block" engine. Block, crank, and rods, should handle 300+hp fine. 2.5 Pistons have a weaker top ring land and won't tolerate detonation. Also has a small Mitsu T04H turbo which will choke at moderate boost levels.

check out the turbo database on http://www.thedodgegarage.com/ it is pretty much accepted as the expert opinion on these engines.