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. 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. On the 7.3 head gaskets, this area is filled in with gasket material and the coolant passages blocked off. Next to each other you can see the differences in gasket material supporting the fire ring on these corners. 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.