I've always wondered why nissan engineers specified that the A-series head will have square ports. It sounds especially silly when you realise that its starts round at the valve and the exhaust manifold has round tube, so why would it transition to a square right at the edge of the head??

I stumbled on an explanation while playing on the net last night. This dude reckoned that flow out of the head wasn't impeded much, but the return flow was. I'm not sure if I agree with him yet.

Has anyone out there in Datsun land ever ported a head so the exhaust ports were round again??? I'm curious to see what effect it has.