What can cause this?
 

We found this in the front passenger side cylinder wall. We were replacing the heads and gaskets. It is smooth, no rough edges or pitting. That is the only area it was seen in. It was not all the way around the cylinder wall or in anyother cylinders. Got any ideas?

We were doing the work due to blown headgaskets. They were finished off at Smokin' after a 444 HP run on the dyno.

You need to upload that picture to your gallery.
The tiny thing in your post looks funny on top of the piston, but you can not even see what you are looking at.

https://www.ford-trucks.com/user_gal...id=115511&.jpg

This is linked from my gallery, as you can see it is big enough to actually see some detail.

racerwoman posted the pics in her gallery. It's a cylinder wall and the consensus is that it's some kind of coolant flash. There were no pits/scuff's in the cylinder wall at all or it wouldn't have gone back together. In fact you can still see the cross hatches from the factory hone marks. I have considered sending it to International for a look/see, but it would probably be a waste of time. Besides the carnage created by the oldstyle predator programming on the headgaskets there weren't even any "daisy's" on the tops of the pistons. A testament to Matt's programming.