This is an exert from an online Hot Rod magazine reguarding coatings. The headers on my Dart are coated inside and out.
As a part of our test, we wanted to quantify the benefits of a coated header versus a plain uncoated black painted header. A thermal barrier ceramic coating adds considerably to the price of any header, often doubling the price. We tested two otherwise identical Hooker 1⅞-inch headers with surprising results. Running on the dyno, we found the power numbers virtually unchanged (see Average Power table on next page). Where the ceramic coating made a remarkable difference is in the heat transferred by the header. We tested the header temperature immediately after a run, and then one minute after shutdown. The coated headers measured 258 degrees F dropping to 195 degrees F a minute after shutdown. In contrast, the uncoated header measured a scalding 870 degrees, retaining 520 degrees a minute after shutdown. We didn’t need a heat gun to tell the difference in the test cell.
Our next test loaded the engine to 60 lb-ft of torque at 2,800 rpm, simulating a high-speed cruise situation. We gauged the surface temp of the header once fully stabilized. Once again, the difference was huge, with the coated header showing 288 degrees, while the uncoated header recorded 850 degrees. While the dyno run didn’t show much difference in output, an engine breathing air from under the hood will definitely feel the effects of that extra 562 degrees F pumping into the engine bay. Taking account the effects of heat on engine component life and passenger comfort, the coated headers are definitely a winner.