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Discussion and questions related to the course Practical Engine Building
Have you tested an engine that had the thermal coating on the valve faces, combustion chamber, and maybe the exhaust port? I've read that valve faces, combustion chamber and piston dome blur hot spots in addition to containing some heat letting the valves run cooler. Likewise, the exhaust port coating should reduce heat transfer to the coolant.
CP talks about coating the dome increasing piston life by reducing heat transfer to the piston. That is probably impossible to measure unless the engine is putting the piston through thermal cycle fatigue. On this vein, some coaters seem to put the thermal coating on the top of the piston while others include the entire piston above the top ring.
The piston manufacturers offer a hard anodized coating over the piston or just the ring grooves. This is CP's description:
"Anodizing the piston reduces wear and material transfer. Anodizing can be done to the entire piston or a selective area depending on its usage. Anodizing the entire piston has been shown to be very durable in drag racing applications, but some pistons require only the ring groove(s) anodized in order to lessen the chance of micro-welding the ring to the aluminum groove."
Is that worthwhile?
I've experimented with thermal barrier coatings on a piston crown but realistically my testing was never in depth enough for me to conclude that it offered an advantage. Thermal barrier coatings on the combustion chamber, valves and exhaust port certainly has some scientific merit but I just haven't had the opportunity to test them for myself.
Hard anodising of the ring grooves is normally used when running very thin rings. By hard anodising the ring grooves and using very tight clearance between the ring and the ring groove, micro welding is eliminated. This isn't a typical problem with a normal off-the-shelf pistons.