For exhaust applications you can find NAS and MS passivated finished stainless hardware that is extra corrosion resistant yet has strength equal to or greater than grade 8. Usually easier to find in racing catalogs and aircraft hardware catalogs.
Here's a few examples:
http://www.ddaircraft.com/subcategory.c ... gory=BOLTS
http://www.aircraftspruce.com/menus/ha/bolts.html
and links
http://www.aircraftfastener.com/




