This is what the failed piston (No1) looked like when it came out
The hair line cracks when given a bit of a wiggle by the tech's resulted in this bit coming off
Its very lucky they noticed the loss of power when they did, another run on the dyno could have dislodged that piece of piston and trashed the bore and potentially the engine.
The good news is the car not only has very good compression now, but the cylinder compressions are also within 1% of each other. From what i gather, OEM tolerances of upto 10% is acceptable
That would be 19psi difference!!