grade 5 or grade 8 bolts?

[70 RAG TOP]

Hey guys

I may be obsessing but I do have OCD so I guess that comes with the territory.  Should the bolts(intake, water pump and other external engine bolts)be grade 5 or 8?  Or does it matter?  If you use grade 5 will they eventually stretch to the point of causing leakage(such as on intake man.)?

Thanks

[Supercuda]

My OE intake bolts are grade 8; 8 is better for any high-torque application, and grade 5 works well in "less-stressed" envronments. Grade 8 was also used on my water pump and exhaust manifolds, but only grade 5 on the oil pan and timing cover. This is on a bigblock; a smallblock uses grade 8 on the timing cover, if I remember correctly. Follow your OCD and use grade 8 until you're blue in the face; insurance can be cheap, and this is it.

[70 RAG TOP]

Thanks for the quick reply.  I will go with the grade 8.

[Chryco Psycho]

I generally use grade 5 , just incase the bolt breaks off like th ealternator pivot bolt tends to do , the grade 5 is much easier to drill out

[dodj]

I generally use grade 5 , just incase the bolt breaks off like th ealternator pivot bolt tends to do , the grade 5 is much easier to drill out

Certain applications like the above mentioned pivot bolt, are not a good place for grade 8 bolts. They will break sooner in those kind of applications.

[Supercuda]

I've been using the same grade 8 bolt in my alternator for over twenty years. It was doing well in the alternator that I pulled it from then, too. Stock on a Chrysler engine from about 1974 or so, and only replaced it in my 1970 383 because the head was rounding, and I needed a different length for the different mounting that I went to.

[72cudamaan]

Certain applications like the above mentioned pivot bolt, are not a good place for grade 8 bolts. They will break sooner in those kind of applications.

 Grade 8 bolts have more strength for thread pull, but since they are more brittle than grade 5 , they will sheer off easier. ( perpindicular to the bolt length ).