The 1.8l is a debored destroked 2.5l. They did that so the mx-3 wouldn't compete sales wise with mx-6. Best bang for the buck is to swap for the 2.5 in either the kl(us spec) or kl-ze(jspec) flavor. You'll need the engine, ecu, vaf . Reuse the intake manifold off the 1.8l (k Bingo! About 30 - 50 more hp and torque. The biggest thing to watch out for is the disty. The igniter module will crap out at some point and the intake tube will crack and cause bad idle.