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Message: <blockquote data-quote="wc9922" data-source="post: 361265" data-attributes="member: 6000">Looking at the cylinder head dome, showns signs of uneven combustion across the cylinder chamber. If the combustion is even, your cylinder head the dome will all be the same color. Some areas are totally without carbon. The combustion flame front is starting more at the exhaust half of the piston as this is where where the air fuel mixture starts burning moving towards the intake side of the piston. While this is normally how it it's designed be, in your case the flame front speed is very rapid ( i.e cylinder pressure rise during power stroke is causing detonation) as you are boosted. The uneven pressure forces causes greater uneven force distribution on the picton crown than design (more on the exhaust side) so the damage was on the intake side piston skirt.  Would image that after you have upped the boost, without the ECU retuned to reduced the timing figures accordingly, it's firing a bit too early causing the combustion flame to move so fast detonation occurs. Lowering your CR would help in your case as mapping is fixed at the moment.  Still not sure why it's break at the ring-groove area specifically like that. What's the story with the cam holder?  Secondly, why is it only happening to your middle 2 pistons #3-#4 only ? By design they should be the 'safest pistons'. Interesting stuff.  Meanwhile go have fun with your new Scooby!!</blockquote>