There is no such thing as grade 8 stainless. The stainless bolts you buy at the hardware store are 304 stainless and the equivalent of a grade 2 steel bolt in terms of strength. There are stronger alloys like 316 which could replace a gade 5 and maybe even a grade 8, but I prefer grade 8 for all engine purposes. Stainless also expands an contracts a lot with temperature variations which could cause the bolt to come loose. Another reason to stay away from stainless on engine parts. Grade 8 has very good corrosion resistance and I use it on everything engine and exhaust related.