I’ve been interested in learning if putting a thermal coating on the exhaust manifolds makes any significant difference in the temperature radiated from the exhaust manifolds.
Additionally I’ve found that people modifying theirs cars are a very optimistic group. If I was to use an Infrared thermometer to take external temperature readings of the exhaust manifold at various points in time, and find no difference between the thermally coated manifolds and stock uncoated manifolds, the optimists would pronounce that the surface temperature of the exhaust manifold is not important, it is what happens to the temperature of the gasses inside the exhaust manifold that matters. If I was to measure the exhaust gas temperature of the thermally coated manifolds against the stock manifolds and find no difference, then what would really matter would be underhood temperatures, that would of course be lower since the thermal barrier slows the passage of heat from the interior to exterior of the exhaust manifold, even though the surface temperature might be the same between the coated and uncoated manifolds.
Desiring to be thorough with the next opportunity to do this evaluation I assembled a few additional sensors so that I could check readings better. On hand I now have an Infrared thermometer, an air temperature probe, a high temperature K-type thermocouple, and RS6 exhaust gas temperature sensors installed on my S4 to record the full range of exhaust gas temperatures.
I also have a stock set of exhaust manifolds currently installed on my S4 and a set of ceramic coated exhaust manifolds available for installation at my earliest convenience.
As a warm up for the more thorough testing I started my car with the air temperature probe placed 2.25″ from the exhaust manifold and took readings every minute with the Infrared thermometer to produce the chart below.