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Discussion Starter · #1 · (Edited)
Trying to find the correct gasket for a pair of 390 GT exhaust manifolds. Just tried Felpro 1442, the one that was suppose to work, and the alignment of the ports and bolt holes is off something terrible.If I match the bolt holes the ports are off….If I match the ports the bolt holes are off. My exhaust numbers are C70E-9431A and C60E-9430A. Any help here?
 

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Edit: (again) You have the wrong gasket, or a gasket that will not accomodate the GT pattern corrrectly.

I can't say what is the correct gasket for your needs, but looking at your pics, I see the gasket has poor matching of the ports as it get closer to the rear of the manifold towards the outlet. The bolt hole used to align gasket is the incorrect bolt hole. GT manifolds only use the bolt holes on the sides of the port, not the ones at 12 o'clock and 6 o'clock. Move the bolt to the correct hole and see if alignment is better. It may be the pic, but it looks like the gasket will "square up" with the ports much better. Also the pic does not show the bottom of the ports. Is the gasket protruding into the exhaust flow on the bottom of the port? On my 390, I have the heads drilled for the CJ 16 bolt pattern. I have difficulty finding the correct bolt pattern and matching gasket that fits my ports. I have had to do a little "trimming" to remove some gasket material from the bottom of gasket so it did not intrude into the ports. But that is because of my LATE MODEL FE heads (D2EAA). This is just a guess on my part. Maybe more pics?

I am going to be going through this issue again soon as I am rebuilding the 390 currently. I ordered the gasket set through the machine shop, and have not even opened it up to see what gaskets I have been supplied. I may be purchasing new gaskets despite having some in my rebuild kit....dang...

NOTE: I also forgot to mention that the 14 bolt GT pattern is different than the 16 bolt CJ pattern in 2 different ways. The first difference is of course is the 16 bolt has 2 extra bolt holes. But the second difference is the 2 outside top bolt holes are located lower than the two inside top bolt holes.

Your bolt is in the wrong location for GT Manifolds. It is in the CJ pattern with the outer hole located higher than the GT
 

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How about the skippets? Make sure the manifold sealing surfaces are flat and bolt them to the heads. I'm pretty sure the FE's, like the small blocks, didn't use a gasket from the factory.
 

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Don’t use an exhaust manifold gasket. You are just asking for trouble by using one.

no gasket = no chance of a gasket blowout.

all you need to do is take the manifolds to a quality machine shop and have them “true the mating surface where the manifold bolts to the head. They won’t have to remove a significant amount of material, The heads are usually very flat without needing any attention. But it doesn’t hurt to check them with a machinist straight edge.

Once you bolt up the manifold straight to the head you will have a minute or two of microscopic leakage that is soon plugged up with carbon. Re-torque the manifolds after they have cooled down and you are good to go for years.

I built my last ‘66 Galaxie 500 XL that way and it never gave a hint of leakage.

Just like factory.

Z
 

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If both mating surfaces are flat, NO gaskets required.
My 67 390 with SCJ exhaust manifolds & Edlebrock heads - I didn't use any gaskets. Quiet for 19 years
 

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Question: do you also need the spacer surfaces trued as well, and then assembled w/o gaskets?
 

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Bostang, not sure why you NEED a gasket there, didn't have them from the factory. BUT, if you're dealing with less than perfect surfaces on the head or the ex manifold, Get soft solid copper gaskets from Hussey or the gasket maker of your choice. The soft copper will comform to the imperfections on either surface AND allow for heat transfer from the manifold to the head, which is what Ford's engineers intended. The paper gaskets and insulator gaskets just cause trouble. LSG
 
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