question on head exhaust port size

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looking at TTI headers for my 75 318 with 70 heads.
TTi says 4wks for small port 318 head at 1.09w x 1.55h.
Larger 318/340/360 exhaust port is 1.30w x 1.80h.
I wasn't aware of the different sizes. Can't wait 4wks.
Thinking about Dougs d453's...they don't list any difference in the exhaust port size.
I measured and get smaller numbers than 1.09 x 1.55.
I find no reference online on exhaust port size on OEM heads.
 
All of them are 360 sized except the <67 antiques. But yes, the 318 has a smaller exhaust port. my 273 on the stand is a 1.00X1.50 and the 360 on the floor is a 1.30X1.70. Thats a 68% or 1.5 inch² to a 2.2 inch² difference in port area. Those are the end ports, the center ports are wider to compensate for the lost corner.
 
Are the tubes for the ports on those headers the same size??? Then I would think that the "port" in the flange wouldn't make that much difference and the larger port for the 360 head would be less restrictive...

Go with the flow...
 
here's where my confusion lies...TTI says:
*For 273-318 Small-port cylinder heads, with the port diameter 1.09w x 1.55h. Applications with these small-port cylinder heads, will require modification to the ports for our headers to seal properly. Additional material will be added to the ports for headers to seal properly. Modification will be done prior to coating.
Are 1970 318 heads considered small port? I know alot of guys here have used TTI here.
Just trying to determine if these are special order or std.
http://www.ttiexhaust.com/MoparClassics-Headers/340-Step/TTi340.htm
 
No coffee yet this AM so I may not be thinking this through LOL.... But I am not sure why the larger port headers would not 'seal properly'....?? Is the machined flat area around the port smaller too? If not, then the small step around the head-to-header interface would usually be considered a plus (to reduce reversion a bit).
 
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Here a 360 exhaust manifold gasket and a 318 exhaust manifold gasket. The 318 (older style) has the blue on it and if you look real close you can actually see daylight through the lower corners when you place the 360 over the 318.:

DSC01769.JPG
DSC01770.JPG

I went with 302 casting heads so that there was no way I would get a leak although there have been some FABO members say not to worry about it.

Treblig
 
Thanks; that is a good demonstration. So the issue is the gaskets and/or the lack of the lower bolts? Based on your gasket sizes, it looks like the flat gasket surface areas around the ports are indeed smaller.
 
nm9stheham said:
Thanks; that is a good demonstration. So the issue is the gaskets and/or the lack of the lower bolts? Based on your gasket sizes, it looks like the flat gasket surface areas around the ports are indeed smaller.
Click to expand...
The 318/273 heads have a much smaller sealing surface around the exhaust ports. The exhaust ports themselves are also smaller.

Treblig
 
You sure that is a 360 exhaust gasket? What are the bottom bolt holes for? Are there some oddball smallblock motors with 4 bolts at that location?
 
Osi
69_340_GTS said:
You sure that is a 360 exhaust gasket? What are the bottom bolt holes for? Are there some oddball smallblock motors with 4 bolts at that location?
Click to expand...
Positive!! The lower holes are for the smog ports. The smog ports (if your heads have smog port) must be plugged.

DSC07643.JPG


Treblig
 
69_340_GTS said:
You sure that is a 360 exhaust gasket? What are the bottom bolt holes for? Are there some oddball smallblock motors with 4 bolts at that location?
Click to expand...
These are 360 heads on a 318. I was told those extra holes are some kind of smog ports that go into the exhaust ports. Mine were plugged by the rebuilder with Allen head set screws. I put 273 manifolds on and gaskets for them which were the same size and type as the blue gaskets shown above and significant parts of the exhaust ports were covered by tbe gaskets. I had to get 360 gaskets instead.

20170704_191428.jpg
 
I think the later 318 heads (with smog ports) have the larger exhaust ports also??? That's I why I swapped over to 302 casting heads ('86 and later small block 318 heads). I had '69 318 heads with the small ports on my Barracuda and when I went with the 340 exhaust manifolds I noticed the big difference in the port size and sealing area, so I swapped out for 302 castings (same CCs as '69 318 heads but larger ports).

treblig
 
Can't you just use the larger port headers and get exhaust gaskets for a 360 to seal them up nice??? Maybe I'm missing something but I just swapped out a 318 for a 360 in my van and went through some of these questions in the midst of it. The 360 gaskets sure looked they would fit and seal right on my 318 heads no problem. The factory manifolds had the larger 360 style ports but were bolted on my 318 and worked just fine.
That way, you leave yourself open for a possible upgrade to bigger heads in the future also.
 
MobileCustoms said:
Can't you just use the larger port headers and get exhaust gaskets for a 360 to seal them up nice??? Maybe I'm missing something but I just swapped out a 318 for a 360 in my van and went through some of these questions in the midst of it. The 360 gaskets sure looked they would fit and seal right on my 318 heads no problem. The factory manifolds had the larger 360 style ports but were bolted on my 318 and worked just fine.
That way, you leave yourself open for a possible upgrade to bigger heads in the future also.
Click to expand...


360 gaskets will fit no problem but they almost exceed the 318 exhaust sealing surface. Like I said before, some FABO members have said that they get them (340 manifolds on an older 318 head) to seal up. But I didn't want to take any chances and besides the 302 heads had bigger ports and a closed combustion chamber. If the OP can get them to seal up then he's in the clear!!
In my case I wanted better exhaust manifolds and getting bigger ports didn't hurt either.

treblig
 
I think I would go for the larger port headers, some Remflex gaskets, and put some JBWeld under those corners on the outside of the sealing surfaces to support the gaskets if I did not feel lucky that day...
 
i just find it odd that TTI is the only one to list small port 318 heads(1.09w x 1.55h) whereas Dougs, Headman, etc do not. They have one size fits all. That's what was confusing.
 
My guess is that because TTI is so well know for great fitting headers, that they aren't taking any chances. Since a 340/360 header might leak on a 318, they just make a special 318 header.
 
FWIW
I ran my TTIs for 5 or probably 6 winters on a stock 1973 teener, with the same gaskets that I ran on the 360 with Eddies. I lost track of all the times those gaskets went on and off, maybe over a dozen times or more. So whatever TTI supplied in 99 worked for me. I think I replaced them in about 2009, when I had to patch the merges, for the second time, but I forget what I put in there. Maybe Mr.Gasket, but I'm guessing.
I don't want to say that the dual full-length 3inch pipes have anything to do with that, but it's so hard not to mention those sewer pipes,lol.I love those!
 
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scored some Dougs d453's.....Jegs matched Autozones 20% off!
Going to breakin rebuilt motor on stock manifolds and then install the ceramic D453's.
 
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