ptuomov

My position is that if you are designing an NA engine ground up, maybe coatings are worth it, or maybe not. In this case, one has freedom to address the heat retention and cooling with cooling passages, materials, etc. However, if you are turbocharging an existing NA engine, one doesn't have those choices. In that situation, TBC on the piston top and combustion chamber make sense. When GM turboed Ecotec for Solstice (spell check please), they put a TBC on the piston top, I believe.

This is for the piston top TBC. The skirt coatings I am sure are used in pretty much all engines now. One difference between top and skirt coatings is that if the coating on the top comes off it'll be blown away thru the exhaust port and doesn't make it to the oil system, while skirt coating may. Still, the friction and wear reducing coatings on the skirt make such a difference that everyone seems to use them now.

One more thing to consider. If TBC coating flakes off and makes in the exhaust, it is probably not going to damage the turbine spinning 150k rpm. Why? This is because the gas, the particle, and the turbine blade all move at about the same speed when they touch inside the turbine.

danglerb

A variable is a variable. Everything that gets changed reduces the chance of a predictable result, or even a result that can be related to any specific thing. Seems like you are rolling a lot of dice at the same time.

ptuomov

This in reference to what? About me keeping the main interfaces and design parameters constant? Surely you must be joking if you mean that keeping the main interfaces and design parameters doesn't lead to a more predictable outcome.

danglerb

No by variable I meant the things being changed, like coatings.

ptuomov

In case someone is interested, here are some ring options for 100mm bore. These are from NPR (Nippon Piston Rings). Apparently, the first application gives the ring set its name.

I don't know if the two options in the middle fit stock piston and run well on Alusil, possibly worth investigating. However, for Nikasil and the pistons of this thread, I am hoping that SWL03190-2 will work just fine. Que sera, sera...

I decided to go with wide rings, which really are much wider than in modern engines for two reasons. First, one less interface change to worry about in case this ring idea turns out to be not so hot. Second, wide rings help with cooling the piston in a turbo car, where the piston may get pretty hot. I am betting that the improved cooling of the piston more than offsets the increased heat due to friction from 1.5mm, 1.5mm, 3.0mm rings.