Civic EG

... between OBD1 and OBD2 engines.

I'm sure there can't be that much different between a 96-00 B16A and a 92-95 surely? What actually MAKES the engine OBD2 rather than OBD1?

I'm intrigued and thought I'd ask.

a few additional sensors- knock, secondary o2, ckf sensor, egr on intake manifold of some obd2 engines. Don't know all about B series, but OBD2 D series have the slightly smaller square shaped combustion chamber.
Also different injector clips and a different location for the IAT sensor and evap purge valve. Mostly the difference is in the electrical/sensors.