Having stripped down and cleaned up the Volvo lump a few weeks back I noticed these odd markings in the centre, any idea what they are? Detonation?

 

its possible -most det leaves pretty bad pockmarks with visible melting though- almost fermentation of the metal are all pistons the same? or just the one-could be just bit of surface damage from carbon coming loose or other light debris

 

One is fine, one has a lonely mark much like these Y and V's, and the other is very similar to the above.