I think 3B got some defective bolts. I have been useing grade 8 on every manifoldv I pull for 40 years. I have put hundreds of 292 manifolds on with them. 292 ex. manifolds are probably the hotest running out there when used on the one ton & larger trucks. They glow red hot after a hard run. I also have used the grade 8 on many small block manifolds & others also. I have never had a broken bolt on any of these. I throw grade 5 bolts in the scrap metal pile when they come with a new part. If a part is constantly stretchred or flexed as it is used it will eventually fail. If a part is strong enough not to give it will last infinitly.
