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Originally Posted by TONY!
Well having a higher torque upon original installation and torquing the head gasket down after many many years is not exactly the same thing.
I would think that the MKIV's have better head gasket sealing due to the MHG and I would think that toyota placed it in between a flat and smooth head and block (what some individuals don't do when using MHG's).
It is said that detonation is one of the biggest reasons for head gasket failures also.
I think the winning formula to for the ultimate sealing would be to get the block and head milled to a low RA (roughness average) of 40 or less and then use Permatex Brake Quiet in the can form and spray that onto the metal gasket, then install the gasket and the head and tighten it to 85-90 foot pounds of torque.
To be honest with you, the reason why so many have bad luck is because they don't do things the right way and take short cuts.
That applies to many other jobs and not just the BHG repairs.
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Good post/info, Tony!
Another piece of (related) info is that the oem head bolts don't hold past about 37psi of boost. Oem-sized ARP's do a little better than that, but many Mkiv Supras running over 40psi of boost have gone to 1/2" ARP studs.
Btw, I'm curious: what does the Permatex Brake Quiet do? Fwiw, I'm aware of a number of 1000hp+ 2jz-gte's built without it, using the oem headgasket, with no headgasket leaks/failures. Will an organic compound like that stand up to 1000hp+ combustion forces? Also, will it make the head more difficult to remove later?