1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

6.9 vs 7.3 Head Gaskets and Boost

Discussion in '6.9L IH & 7.3L IDI Diesels' started by Thewespaul, Mar 13, 2020.

  1. Thewespaul

    Thewespaul Supporting Vendor Supporting Member

    Posts:
    8,378
    Likes Received:
    7,016
    Joined:
    Jul 27, 2015
    Location:
    Bulverde, Texas
    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.

    1C8F2B22-97CC-4077-898C-06328F121DE3.jpeg

    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.
    7502BB50-3FC9-4D8C-B7E0-64E95C224A48.jpeg
    On the 7.3 head gaskets, this area is filled in with gasket material and the coolant passages blocked off.
    00044FEB-1E5A-4176-8A17-D383B5264FB0.jpeg
    Next to each other you can see the differences in gasket material supporting the fire ring on these corners.
    A775D79F-0FBB-4207-848A-3A3CCB435E90.jpeg

    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.
     
    Last edited: Mar 13, 2020
  2. frankenwrench

    frankenwrench overkill is under rated!

    Posts:
    597
    Likes Received:
    306
    Joined:
    Oct 8, 2017
    Location:
    Weatherford tx
    Which ones are the idit hg's?
     
  3. Thewespaul

    Thewespaul Supporting Vendor Supporting Member

    Posts:
    8,378
    Likes Received:
    7,016
    Joined:
    Jul 27, 2015
    Location:
    Bulverde, Texas
  4. IDIBRONCO

    IDIBRONCO IDIBRONCO

    Posts:
    5,127
    Likes Received:
    3,354
    Joined:
    Feb 5, 2010
    Location:
    edmond, ks
    How are you planning to modify the head gaskets? I'm curious because I believe that there's an extremely good reason for the insert tabs to be there versus just using another hole in the gaskets. I feel that the rubber-coated steel inserts are vital. The large coolant holes (in the gaskets) in the upper two corners reinforce this belief for me.
     
  5. Philip1

    Philip1 Full Access Member

    Posts:
    99
    Likes Received:
    64
    Joined:
    Apr 1, 2019
    Location:
    Nevada
    So when you modified the gasket did you just drill a hole in the gasket where the coolant passage is?
     
  6. aggiediesel01

    aggiediesel01 Full Access Member

    Posts:
    186
    Likes Received:
    138
    Joined:
    Dec 29, 2016
    Location:
    Houston, TX
    on edit: nevermind, that set is still in the back seat of our '91

    I think you might have a pair to pic and post up for public consumption; when you have a min look in the International top end set box in our '93. That is a specific turbo top end set it should have a set of turbo gaskets. My dad thinks he left them in the box of stuff he sent down with that truck along with a set of 6.9 gaskets.
     
    Last edited: Mar 13, 2020
    Thewespaul likes this.
  7. aggiediesel01

    aggiediesel01 Full Access Member

    Posts:
    186
    Likes Received:
    138
    Joined:
    Dec 29, 2016
    Location:
    Houston, TX
    In the shop truck build it looks like he put the inserts in and then cut them to allow the water to flow but in big blue I didn't see any pictures of how he did it. I would think that the inserts, even with the hole, might help support the gasket in this area but maybe not enough?

    From Shop Truck thread click the attachment to see:
     
    Thewespaul likes this.
  8. Thewespaul

    Thewespaul Supporting Vendor Supporting Member

    Posts:
    8,378
    Likes Received:
    7,016
    Joined:
    Jul 27, 2015
    Location:
    Bulverde, Texas
    From top to bottom, approximate fire ring thicknesses:
    6.9- .0940”
    7.3T- .1750”
    7.3NA- .1035
    D97FDAE4-C8CA-494C-9727-3DEB34F52D4A.jpeg
     
    Fision and Dirtleg like this.
  9. Thewespaul

    Thewespaul Supporting Vendor Supporting Member

    Posts:
    8,378
    Likes Received:
    7,016
    Joined:
    Jul 27, 2015
    Location:
    Bulverde, Texas
    Note that the engine with the cut out inserts was the idit, and the latest na engine I left them alone like how they came on the 6.9s, wanted to try and keep coolant flow even between the cylinders, I actually saw better coolant temps with the na engine that had just the stock inserts, been doing it that way every since.
     
    Fision, Macrobb and aggiediesel01 like this.
  10. aggiediesel01

    aggiediesel01 Full Access Member

    Posts:
    186
    Likes Received:
    138
    Joined:
    Dec 29, 2016
    Location:
    Houston, TX
    Somewhere I read that all new 7.3 gaskets were the turbo style. Looking at your pics and the coffee table book, looks like that might be correct. the scallops for the lower head bolts and the odd little hole outside the fire ring look like whats in the coffee table book.
     
    Thewespaul likes this.
  11. Thewespaul

    Thewespaul Supporting Vendor Supporting Member

    Posts:
    8,378
    Likes Received:
    7,016
    Joined:
    Jul 27, 2015
    Location:
    Bulverde, Texas
    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.
     
  12. frankenwrench

    frankenwrench overkill is under rated!

    Posts:
    597
    Likes Received:
    306
    Joined:
    Oct 8, 2017
    Location:
    Weatherford tx
    What are these inserts I keep reading about? Pardon my ignorance
     
  13. Ilovelamp

    Ilovelamp Full Access Member

    Posts:
    250
    Likes Received:
    70
    Joined:
    Jun 16, 2019
    Location:
    Arkansas
    That is quite a dramatic failure!
     
  14. aggiediesel01

    aggiediesel01 Full Access Member

    Posts:
    186
    Likes Received:
    138
    Joined:
    Dec 29, 2016
    Location:
    Houston, TX
    Second pic in post 1, these are 6.9 gaskets, in the little supplement bag on top there's a couple "superman" shaped objects. 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.
     
    frankenwrench likes this.
  15. frankenwrench

    frankenwrench overkill is under rated!

    Posts:
    597
    Likes Received:
    306
    Joined:
    Oct 8, 2017
    Location:
    Weatherford tx
    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
     

Share This Page