This is an interesting  picture from the Mazdatrix web site.

This must happen around  four hundred HP per
rotor on turbo engines :-) I suspect it is caused by detonation
at that power level as it is in the right place on the 
rotor flank where detonation occurs. Lower compression ratio
anyone? :-) It could also be caused by inadequate rotor cooling
at that power level.

Paul Lamar
 
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