One other thought, I have heard both sides of this argument before as well. I also heard it is nearly impossible to weld / repair pipes with this coating. I found a solution that solved the problem cheaply without making the pipes more difficult to weld. I wrapped my entire exhaust system with hot rod exhaust wrap. I bought it at the local auto parts store in the 1" width. Spruce sells it as well. I tested the stuff with a torch in the hangar on my hand and was amazed how well it insulates. I have 2 layers in some very hot places on the pipes. In addition to reducing the inner cowl temps, It also tames the vibration of the pipes and reduces noise. Cheap, relatively light and effective... Fwiw.
Randy Snarr N694RS 235/320
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I think it is about radiation. The reason I did it was to reduce the amount of heat radiated back at the cylinder heads. While a shiny reflector might be more effective in theory, installing it everywhere you would want it on a TSIO550 exhaust system is a lot of work.
On Jan 12, 2012, at 8:46 AM, Gary Casey wrote: I guess I'm just not convinced about the effectiveness of typical ceramic coatings. From what I can find out they are typically .001 to .002 thick, about 5% of the thickness of the metal. In order to significantly reduce the heat transfer compared to the metal, they would have to have thermal conductivity in that order compared to steel. I can't find out what material is used, but some might use zirconia, a very good insulator, which has about 10 to 20% of the conductivity of steel. But that's not the whole story. Inside the pipe is a gas at perhaps 1500F moving at a relatively high velocity. The conductivity to the metal is therefore relatively good, resulting in a metal temperature of probably 1200F. The air on the outside is at about 180F and it is moving slowly, so the heat
transfer from the pipe to the air is "poor." My guess is that the surface temperature of the ceramic is going to be very close to what the metal would be without the coating. There just isn't enough thickness for it to be well insulated. Swain Technologies has a proprietary process that puts .015 thickness on metal and that would probably work. A big factor in heat transfer is radiation and the best way to reduce that is with a shiny metal surface spaced away from the exhaust pipe, or from the device to be protected.
Maybe ceramic coatings work well, but I'm afraid I'm not convinced.
Gary Casey ES 157
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