[Badbubba]

Originally Posted by 2010 4 DW

I used a Pyrometer when I did my testing and both sets were with the car running at idle for five minutes. The ceramic set was coated inside and out also.

Some of those allow you to adjust the emissivity, others no. If the uncoated headers were new/polished when you measured the temp, then I'd say the temp difference between the two is fairly accurate. If the uncoated headers were not polished and were on the car for awhile, allowing the surface to change, then the temp difference would not be representative. In other words, different surfaces give off different amounts of infrared energy at the same temperatures and the pyrometer measures that amount of "energy" (acutally it measures amplitudes/frequencies in a fixed wavelength spectrum). A "shiny" surface will give off less IR energy (radiation) than a corroded surface. Thus, if you heated up an old header and a new shiny one to the same temp, the pyrometer would display a lower temp for the new shiny one. Emissivity is the correction factor for different surfaces. I know a few people who did a case study with Jet Hot coatings, well worth it. To sum it up, go with a coating.