Take a look at the temperature difference between manifold exhaust port #1 and the turbine housing. I'm thinking that retarded timing is not burning all the fuel in the combustion chamber and allowing the fuel to continue burning in the exhaust; creating more heat outside the cylinder. In some situations that can be desirable but this, I do not believe, is one of those situations.

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1991 F250 super-cab 7.3 IDI. (rebuilt by me) Banks Sidewinder turbo, hydroboost brakes, new IP and injectors.
2003 S430 - 107K
1983 300SD - Tanoshii - mostly restored ~400K+.
1983 300SD - Good interior. Engine finally tamed ~250K.
Monark Nozzle Install Video - http://tinyurl.com/ptd2tge