Can anyone tell me if the cylinder heads with stamp code 30P are compatible with cylinder heads with stamp code10Y ? What are the differences ?

They are compatible only if you match the lower intake with the corresponding heads. There where very slight changes to the intake side ports due to newer style injector change in ‘93. The 10Y heads need to be mated with 93+ lower intake (ie the part that new phase 2 injectors bolt onto). Although both heads seam to “fit” but the intake ports are slightly offset. Check out the z32 wiki below, about half way down.

https://conceptzperformance.com/wiki/in ... inder_Head

Thank you so much. I have a 1990 #00ZX NA that I've had since 1989. That explains why I'm having low compression on several cylinders. Guess I'll pull the heads and have the intake valves replaced.