I lifted this straight from the dodgegarage. Here is what Gary D. has about piston coating. You can find this on the dodgegarage in the turbo database under the category for shortblock. The note: is part of that info too.
There are a variety of skirt and top coatings for pistons- The Teflon coatings on the skirts reduce wall friction, coatings on the underside help shed oil and ceramic coatings on the top help reflect heat back into the combustion chamber and help protect the piston in case of excessive EGT temperatures.
Note: A noted engine builder has warned me that coatings on the top of the piston may protect the piston but will reflect more heat back into the engine making it more prone to detonation.
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