Ran in to a problem last year where the head started to flex upward between all the combustion chambers. The head literally lifted itself of the deck surface on the engine block even with ARPs and perfecty even surfaces.. This let compression leak in to the cooling system quite badly. At the time it was happening I didn’t know what it was causing this.
Started to investigate in this problem, ran into some guys that have had similar problems once going over 500hp, but never knew why it happened like me.
Eventually I began talking to a friend who used to work at Trollspeed in Sweden. Reinforcing the head was apparently quite common problems on race applications, the pikes peak Saab for example had this mod. All the rallycross saabs got them aswell since they could flex so far that they cracked.
The pics above shows about half the process. I had to drill a 14.2mm hole in the middle between ever spark plug hole. There is a big cooling channel thar runs through the head. I measured the depth and height of the head, quickly realized that there is only 9.50mm of material from the bottom cooling channels and the deck surface.
I tapped the hole to a M14 thread and then took a 10mm mill with a long adapter to get down there. The bottom of the channel is V-shaped so I had to carefully make flat spots for the threaded rods I have make later to even out the load better to get max strength.
Haven’t done this step yet, but these threaded rods will be made in aluminium bronze which will be threaded in M14. These needs to be custom made in a lathe. Once they are done I have to put a extensive amount of thread sealant on them and torque them down to around 45-50nm in all the three holes. This will make the cylinder heads deck surface bulge outwards a little bit on the small wall between the chambers. This creates the tension and support that is needed to keep the cylinder head from lifting and cracking. The final step is to resurface it just until the bulging is gone and no more.
The quest for a indestructible engine continues lol..