High Intake air temp on boosted engine

Could a high intake air temperature above 55 degree Celsius melt a piston under extended period of wide open throttle ?

Well it depends on the fuel and how optimized the tune is. The high IAT by itself won't melt the piston, but it can lead to detonation which will definitely melt/break pistons.

I saw one case ( 2jz engine ) , pistons number 1 and 6 were melted not broken on the intake side. AFR 11.5 , boost 24 psi , 93oct fuel. spark plugs were intact.

Unless you've individual lambdas, that 11.5 is an average - the end cylinders could easily be running a little lean, which could overheat and soften the piston crowns, allowing them to collapse/melt under load.

I'd add to what Francis said - if it were to be a factor you would expect signs of it on all cylinders. Intact spark plugs, as such, mean little - what were they looking like, did they appear to be running lean (white porcelain), and speckles or deposits?

Were you using stock or aftermarket pistons, oil sprayers for the pistons, what manifold, did you check the injectors were flowing the same fuel, etc?

It would also depend on compression ratio and fuel octane rating. Intake charge temperature usually raises in power of 1.4. Detonation usually occurs at about 280-300 degress C on 93 pump gas. High compression ratio will make it worse as it requires higher octane rating fuel.

55 C in power of 1.4 is about 273 which is lower than detonation temperature threshold so it should be OK providing that enough fuel is getting to the cylinder to cool down combustion chamber temperature as was explained above...

CP Pistons, stock intake manifold , 2JZ-ge Block so no oil sprayer under the pistons. How much ignition retard should be used per 5 degree increase of intake air temp ?