6.9 vs 7.3 Head Gaskets and Boost

aggiediesel01 said:

Those can be used on a 6.9 to block the flow of the outer ports like the later style 7.3. Or they could be modified to allow some amount of coolant to pass, or left out completely as it seems that the 6.9s were built.

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Thewespaul said:

I’m thinking of just chucking a small deep well socket in the lathe, cutting and sharpening it into a die to precisely cut the coolant ports, I talked to Justin about it and he said he’s run 7.3 gaskets on a 6.9 without issue.

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Thewespaul said:

I’m thinking of just chucking a small deep well socket in the lathe, cutting and sharpening it into a die to precisely cut the coolant ports, I talked to Justin about it and he said he’s run 7.3 gaskets on a 6.9 without issue.

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Booyah45828 said:

I noticed the mahle branded gaskets appear different on summit's website. Might be better?

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IDIBRONCO said:

Not quite. The 6.9 head gaskets do have a small hole for coolant flow from the factory. In post #9, Wes said that he saw better (I assume this means lower) coolant temps by not enlarging the coolant hole in the 6.9 inserts.

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frankenwrench said:

Thank you for clearing that up. Makes since now. Lol. And thanks for the non judgemental answer as well. Felt kinda dumb not knowing that

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Booyah45828 said:

I see all your examples are from felpro. Have you tried or looked at other brands? I noticed the mahle branded gaskets appear different on summit's website. Might be better?

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Thewespaul said:

Some of you who are following along project big blue will already know that we had an odd head gasket failure at around 25 psi. Hg failures above 15 psi on a 7.3 a fairly common, however this engine was recently studded and retorqued to 130 ft lbs at various temperatures to ensure the gaskets were sitting flat and clamped evenly, despite those steps and running nearly double the amount of boost through the same studs and gaskets in the shop truck, this head gasket split at the fire ring and failed in a dramatic way.

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Failures like this are the best opportunity to learn more, and this weird failure at a relatively low boost pressure has been on my mind quite a bit.

For some time many of us have been converting to 6.9 head gaskets to open up more coolant ports in the head and have found a significant drop in coolant temps when running them over the 7.3 head gaskets, now after having this failure I think the 6.9 head gasket conversion actually contributed to the problem. If you look at a 6.9 head gasket like this, you will notice the large pockets in the corner of the gasket where the coolant insert is placed.

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On the 7.3 head gaskets, this area is filled in with gasket material and the coolant passages blocked off.

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Next to each other you can see the differences in gasket material supporting the fire ring on these corners.

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For the longest time I was under the impression that this change in the head gasket was due to increasing pressure from the epa wanting to cut down on cold temperature emissions from unburnt fuel by keeping more heat around the cooler cylinders, which could still be true, but I think international was also concerned about the increased performance of the 7.3s with their increased cylinder pressure and wanted this area of the fire ring better supported, this was also telling by looking at their improvements to clamping force on these gaskets when they went to 1/2” fasteners on the 7.3s, and in the idit head gaskets actually increased the diameter of the fire ring more when they added a turbo to the 7.3 engine.

Moving forward I plan on running 7.3 na head gaskets with modified corners to flow coolant like the 6.9s, just with much more material intact in that area since it won’t be using an insert. If your engine has 6.9 head gaskets I wouldn’t worry about them, I don’t think there is anything wrong with these gaskets and they are likely the best option for na engines or engines with stock turbos that won’t be seeing much boost, I’ve personally taken these gaskets to 50+ psi without any failures in na 7.3s and had them last in studded 6.9s up to 30 psi torqued at 100 ft lbs, so they can certainly handle boost fine, they just seem to be more susceptible to fire ring issues due to the lack of support in the corners of the gaskets.

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