Whats up with these exhaust valves?

I'll post a pick of a piston when I get home later today. They didn't have any noticeable golf ball type damage to them that I remember. Most of the engines run time was on e85 with 36 degrees of timing. Detonation was my first thought too but I was thinking I remember the pistons looked to good. I was running without an air cleaner. I'll have to examine the pistons closer so I can stop scratching my head. Thanks guys