"So, all those racers out there (motorcycles, quads, drag cars, sand rails, drag boats, snowmobiles, etc.) with heat coatings on top of their pistons are only using it to "feel good"?"
No.
You fail to understand the thermal problem. Ceramic coating piston tops and cylinder head cavities has been shown to gain 1-2% more horsepower at full power. I had my pistons and cylinder heads coated for this reason, and because it made me feel good.
But it works on pistons because the thermal event lasts through the power stroke only, about 180 degrees of rotation, or about 12-15 milliseconds. The peak heating only occurs for about half of this when the pressures and temperatures are highest. This is when most of the power is made, and avoiding a bit of heat loss for a few milliseconds is worthwhile.
Here is the difference between pistons and exhaust pipes. In case of the piston, the thermal "wave" from the transient heating only penetrates a few mils into the ceramic coating during the event. Then the gas temperature falls dramatically, falls some more during the exhaust stroke, and then there is a blast of cold air and evaporating avgas taken in and compressed. The top few mills of ceramic coating are cooled, a reduced amount of heat reaches the piston or head metal, and the cycle continues.
Contrast this very rapid transient piston heating and cooling with the exhaust pipe. Blast of hot gas, then slowing of the hot gas, then some oscillations of hot gas back and forth in the pipe, and then another blast of hot gas. A thermocouple buried in this rapidly changing flow can not respond fast enough to report instantaneously, and displays an "average" temperature which we interpret as the EGT. So does the inside of the exhaust pipe.
With no cooling event occurring, the thermal coating inside the pipe soaks up energy, temperature rises and stays high, and the interface between ceramic and metal gets hot. Then the metal gets hot and it stays hot. Everything gets red hot. This is not aluminum piston country.
The ceramic coating inside the exhaust pipe reduces the heat flow to the metal a bit, but only a small bit. The metal still gets hot, but its temperature is lowered slightly. Even slight lowering of temperature helps a little bit, so it is up to you to decide if it is worth the cost and effort. If it feels good, then do it.
Don't disparage things that feel good. That is why we fly, build nice airplanes, and enjoy sex. Don't knock it.
Gary also wrote: "On a side note, I know it sure keeps my chrome motorcycle pipes from turning brown or blue. Oh, and they have not shown symptoms of failure after years of use. Read below."
Come on, Gary, to you seriously consider a motor cycle spending most of its life at low power settings to be comparable to an aircraft engine running 50F lean of peak at 65% power? If you want to make it a good comparison, open the throttle on your motor cycle, accelerate up to about 90% of top speed, back off the throttle to hold this speed, and then continue for 1000 hours. After that I would like a report on your chrome exhaust pipes. Then we have something to compare and discuss objectively because only then will the operating conditions and duration be approximately the same.
...Don't do it. It will droop off due to gravity having absolutely no creep strength, and will drop in a heap in a few hours. And it will rust to dust in a few cycles....
...Mild steel has no capability in this operating regime.
Gary wrote further: "Why is it then that there are hundreds, no thousands, of experimentals out there (several at this airport) with steel [my emphasis added] exhaust systems that have been flying for years, decades, with no problems or symptoms that you describe?"
I am sorry if the context of my comment in italics above evaded you. The question I was responding to was about using mild steel for aircraft exhaust pipes. Pursuant to earlier emails discussing I noted that even stainless steel had low creep strength at the higher temperatures of interest. Mild steel has virtually no creep resistance or oxidation resistance at the same temperatures. Build mild steel headers for your airplane and when they get hot, they will get soft, creep, and deform. I will leave it to you to look up the creep strength and oxidation rates of mild steel in the temperature range of interest for this discussion, namely 1200-1500F.
As to your comment about experimental (aircraft ) operating for years with no problems, let me again clarify since it appears my earlier text was unclear in conveying its message. I was referring to mild steel (considered to be 1020, 1030, etc. ) while aircraft exhaust pipes are all made with a steel alloy normally referred to as STAINLESS steel, usually 321 stainless, an austenitic alloy with a mix of properties making it attractive for exhaust pipes on airplanes. Unlike mild steel which is almost entirely iron (Fe) with a bit of carbon and low quantities of other alloying agents, 321 stainless steel has the following alloying agents:
Fe, <0.08% C, 17-19% Cr, 9-12% Ni, <2% Mn, <1% Si, 0.3-0.7% Ti, <0.045% P, <0.03% S Translation: lots of nickel and chromium and important additions of titanium. What this means is summarized as follows:
"Grades 321 and 347 are the basic austenitic 18/8 steel (Grade 304) stabilised by Titanium (321) or Niobium (347) additions. These grades are used because they are not sensitive to intergranular corrosion after heating within the carbide precipitation range of 425-850°C. Grade 321 is the grade of choice for applications in the temperature range of up to about 900°C, combining high strength, resistance to scaling and phase stability with resistance to subsequent aqueous corrosion." See http://www.azom.com/article.aspx?ArticleID=967 for more insights.
Mild steel it ain't.
I hope this helps your understanding.
Fred Moreno