I have a square port header that came with (not on) the '73 240 I just bought. The car has a N47 on a f54 block and a stock, smog manifold (not sure if its from the original L24 or the L28). My question is, can I mate up the square port mani with the round port (as I understand it) head, or would i be better off trying to barter the square port mani for a round port one?

I've spent some time combing the archives but haven't found the specific answer-sorry for any redundancy, and thanks for any advice.

You would be MUCH better served getting your hands the proper manifold. You could probably bolt it up but truth is your car wouldn't run worth a darn.

Bajcsi

round port heads are the late heads- L28. You cant use the round header on the square ports... they wont seal. I purchased mine from MSA for $209.00 and it was worth the price.

Just my two cents

Kirk

You would be MUCH better served getting your hands the proper manifold. You could probably bolt it up but truth is your car wouldn't run worth a darn.

Bajcsi

And your advice is solid because of personal experience?

Here in Australia, we never got round port heads until late......on some of our EFI R30 Skylines we got the N47 round port head. But as a consequence of their late arrival and very limited demand, round port headers were never offered.

When I bought an N47 head and used it on an L28 I had, I had no option but to use the square port gasket. Round port gaskets didn't exist. (What Nissan would sell you would be a gasket with the exhaust ports cut out and the sides angled, a bit like a diamond shape.) The square port gasket worked well and didn't leak at all.

There is talk about a phenomenon called 'anti-reversion' and some guys actually build headers to take advantage of this. I think that by using a square header on a round port head can mimic this. I have no hard evidence for you but the theory would seem to hold up when you look at the parts. It certainly didn't drop any power when I used this setup.

Cheers.