Does a 1989 civic si engine fit in a 1990 civic lx?

Yes, a 1989 Civic Si engine can fit in a 1990 Civic LX with some modifications. Both vehicles share similar chassis and engine bay dimensions, making the swap feasible. However, you'll need to consider compatibility of engine mounts, wiring harnesses, and potential modifications to the exhaust and intake systems. Overall, while it's a doable project, be prepared for some additional work to ensure everything functions correctly.