I had a couple of manifold bolts break off on the drivers side and luckily a local muffler shop was able to tack weld nuts on the bolt ends to get them out saving the pain and expense of pulling the manifolds to replace the bolts. Now I have some snapped off on the other side. Why are the bolts so small in diameter? Wimpy if you ask me. Are there better bolts out there? Would hate for one to break off flush with the head!

 

You can reverse tap them out if they break flush. When I put my headers on I replaced all my exh bolts with Grade 8 bolts and anti-seize.

 

Exhaust manifolds/headers and bolts do spike to over 1000 degrees F. Those bolts have to temp cycle thousands of times in their lifetime. Stress corrosion cracking due to thermal effects is probably the most dicfficult problem for bolt manufacturers to overcome. It usually comes down to money. If an OEM can put a good bolt (not great) to hold the exhaust together and not have a ton of failures while the vehicle is under warranty, then they saved some money, which saves you money. Or they could throw the best bolt possible in there, and it possibly be way overkill for 90% of the vehicles and cost more to the consumer...

It's not an easy problem to solve, and it's not a safety issue like the bolts holding the suspension together, or a catastrophic $$ issue if the connecting rod bolts let go inside an engine...