I know this sounds pretty stupid of me, but how can I tell if I have square ports or round ones without taking the manifold off? I was thinking of getting a set of headers, since they seem to be going for fairly cheap.

 

The easiest way is to look at the casting number, which is on the other side of the head towards the front. As far as I know the square port heads are E31, E88, N42, and P90 (turbo). The N47 head has the round ports, and the P79 (ZX) head is diamond shaped.

Phil

 

P79 diamond? I've never heard of that before. I think the P79 is lumped along with the round port heads. Maybe their exhaust runners are a slightly different design than the N47... but so far you're the first to mention it.