Originally Posted by MrFatbooty
Z6 is from '92-'95 and is run by an OBD-I ECU, Y8 is from '96-'00 and run by an OBD-II ECU. Aside from that the main differences are in piston dome and combustion chamber volume.
The combustion chamber shapes are also different. The d16z6 has a hemispherical shape and the d16y8 combustion chamber is squared. The d16z6 combustion chamber holds more volume than the d16y8. Because of the d16y8 smaller combustion chamber, the head yields higher compression than the d16z6.