I recently bought a SOHC VTEC head I intend to swap onto my 91 Civic Si. There are two different D-series SOHC VTEC heads, one from the later model Civic EX (96-00 D16Y8) and one from the earlier Civic Si (92-95 D16Z6). I have been told that the post swap compression ratio's between the two heads are hugely different. One resulting in prox a 9 to 1 and the other an impressive 11 to 1. Does anyone know if this is true and which one is which? The head I have is maked with "P2j-3" and "97" on the exhaust side of the head, If anyone can tell what motor this head is from please let me know. Thank you in advance for any help, this is my first "Inter-motor" mating attempt!!!