Hi Shayne----------Assuming the engine is set up with a stock head gasket, the compression ratio would be 8.29:1 with dished pistons. With flat top pistons, it would increase to 9.82:1. I'm sorry, I don't know how to id a Maxima head. I do know they have a smaller combustion chamber than the N-47 Z head, so the compression ratio would be higher. Hope this helps.
The N-47 head came on '77-80 zcars. If your car is between those years, it's probably a z n47 head. If your engine is not stock, and you have a maxima n47 head, you will have much higher compression(somewhere between 10:1 and 11:1 area, depending on which pistons and head gasket). Here's one idea: I don't know about the zcar n47 heads, but my maxima n47 head on my 240z has a hole on the passenger side near the rear of the head for a sensor to screw into. I think it's for a head temperature sensor or something like that. It's just below the fifth or sixth spark plug, I think. not sure, it's too cold out to go check right now. The zcar n47 head may not have that sensor. That's just a thought though. I'm not sure. I just know every n47 maxima head I looked at in the junkyard had it. Anyway, good luck