High egt results from excessive air in the stoichiometry. Hot flame is oxidizing and burns the pistins OR the piston ring lands off of the pistins. They're made of aluminium alloy and have a low melting point. A 1200°c flame will destroy a piston in seconds. 700°C is fine since there is a degree of cooling occurring. Watching the flame or egt (same bloody thing) means you are seeing the affect of how much fuel is in the air your turbo is pumping in there. High temp tells you some bad stuff is happening you get off the throttle ,turbo spools down and temps drop cause there is Less air in the ratio between the fuel that pump is delivering to the injectors. Temps drop you nurse it home. Back to the tuner to get more fuel tapped in.
