Square Port Headers on Round Port Head

[Muzez]

Is there anyone who has used a set of square port headers on a round port head for any duration?

If yes, did they leak? And if no leaks, what gasket did you use?
 

Confession time. Almost 2 years ago, I bought my Z and I knew almost nothing about it (thanks to you guys and school of hard knocks, we can advance this knowledge level at least slightly :p). I saw an offer for a set of headers listed as “round port” MSA 6 to 1 headers for 1978 Datsun 280z and said ideal! and bought them for a steal. They didn’t look entirely right, but I didn’t know any better ( shame on me). Fast forward to today and I am getting ready to install and realize why they don’t look right: they are square port. 

I cruised through the forums and found some people who say they worked fine without leaks and some who say don’t mess around with mismatched ports. Wouldn’t mind saving the $300 if they will bolt up fine, but don’t want to risk damaging the engine. 

[grannyknot]

They will work but the exhaust gases coming out of a square runner are going to hit the outside edges of the header plate just as you see it in your pics.  That will slow down some of the exhaust gas and cause turbulence and rob you of a few HP.

Depending on how thick the header plate is you may be able to grind the round opening into a squarish shape with a slope going into the header and eliminate some of the turbulence, but not all.  Not ideal but it will work, you can always buy a square port header at a later time.

[kully 560]

I am running and have been running a square port header that is jet hot coated  on a n47 round port head for years . I did use a gasket I purchased from msa at the time,and  I believe it might have been the oem brand. no problems at all with that set up but you will have a problem if you use a squared port head on a round port header !

[siteunseen]

Here's the best exhaust gasket you can get from local dealership. They'll have to order it but you won't pay shipping.

 

 

[texasz]

@siteunseen, do you have any information on the gasket...specifically the different material around the exhaust ports???  

[siteunseen]

Metal. It's fantastic too. Here's a thread talking about it...

 

 

[Zed Head]

10 hours ago, Muzez said:

 I saw an offer for a set of headers listed as “round port” MSA 6 to 1 headers for 1978 Datsun 280z and said ideal! and bought them for a steal. They didn’t look entirely right, but I didn’t know any better ( shame on me). Fast forward to today and I am getting ready to install and realize why they don’t look right: they are square port. 

 

The picture you posted is of round port headers.  They should work well with your lined 77 N47 exhaust outlets, which would be considered "round". The square outline is from square holes in the gasket used.

Edit - if you have an N47 head on your engine.  That's the key.  Can't remember exactly when the change was, it might have been internally oiled cam in 77 and lined heads in 78.

Edited November 30, 2020 by Zed Head

[grannyknot]

2 minutes ago, Zed Head said:

They should work well with your lined 77 N47 exhaust outlets,

@Muzez, didn't know you had an N47, you'll be fine.

[Zed Head]

1 hour ago, grannyknot said:

@Muzez, didn't know you had an N47, you'll be fine.

I'm not positive on it.  One of those things you have to check, even if you know the year.  Lots happens over 40 some years. 

http://www.zhome.com/ZCMnL/tech/head.htm

p.s. I don't think the advice about replacing an N47 head with a P79 head is good.  Unless he changed pistons also.

Edited November 30, 2020 by Zed Head

[siteunseen]

My 9/76 had an N47. Felpro gasket will work. They cover them all with "diamond " ports.

[Muzez]

Hi guys, sorry I have been AWOL today. Was at the junkyard and then getting a much needed shower haha.
@Zed Head and@grannyknot I have the N47 head so I should be fine. Thanks for the catch on the square mounting being okay. They never show what the ports look like in the photos, so I was looking at the rounded shape of the mounting on the new MSAs thinking that was the differentiator. Was thinking "man I am screwed"
@siteunseen and you can use that gasket on aftermarket headers as well?

Will update the thread with photos once they are installed. ;)

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