Mark1965TR4aBRG Posted February 19, 2016 Report Share Posted February 19, 2016 Mine's something like this... Quote Link to post Share on other sites
john.r.davies Posted February 19, 2016 Report Share Posted February 19, 2016 (edited) I've said before how sceptical I am about this subject, for two reasons. 1/ I did wrap my tubular, mild steel manifold with fibreglass strip once. After it got tatty and torn, I took it off, to find the manifold in a sorry state. Heavy rusting , with in some places, 'leaves' of rust, like onion skins came off. Weird blue, orange and black discolouration. 2/ I used to base my criticism on a comparison between the fraction of a millimeter thickness of ceramic coating and the six inches of ceramic insulation that the Space Shutrle carried, when the temperature difference was not far away from what there is inside an exhaust manifold. Then a kind person explained "emissivity" to me. This is the coefficient of thermal radiation, and a "black body", a theoretically perfect radiator would have a value of 1, which for the best heat retaining surface that radiated no heat at all, however hot it was, would be 0. Fibreglass has an emissivity coefficient of 0.75 Stainless steel is 0.59 MIld steel is 0.24! (It gets a lot more radiant once it gets an oxidised surface. About 0.8) Ceramic Zirconia on steel has an emissivity of around 0.5 So, fibreglass makes even stainless steel a BETTER radiator of heat. It does nothing to keep heat away from anything else, but makes it worse! And a ceramic coating on stainless is a waste of money. It makes mild steel a much better radiator, althogh what it really does is protect it from rusting. So, for best value, a stainless manifold, and leave it naked! John Edited February 19, 2016 by john.r.davies Quote Link to post Share on other sites
Mark1965TR4aBRG Posted February 19, 2016 Report Share Posted February 19, 2016 I've said before how sceptical I am about this subject, for two reasons. 1/ I did wrap my tubular, mild steel manifold with fibreglass strip once. After it got tatty and torn, I took it off, to find the manifold in a sorry state. Heavy rusting , with in some places, 'leaves' of rust, like onion skins came off. Weird blue, orange and black discolouration. 2/ I used to base my criticism on a comparison between the fraction of a millimeter thickness of ceramic coating and the six inches of ceramic insulation that the Space Shutrle carried, when the temperature difference was not far away from what there is inside an exhaust manifold. Then a kind person explained "emissivity" to me. This is the coefficient of thermal radiation, and a "black body", a theoretically perfect radiator would have a value of 1, which for the best heat retaining surface that radiated no heat at all, however hot it was, would be 0. Fibreglass has an emissivity coefficient of 0.75 Stainless steel is 0.59 MIld steel is 0.24! (It gets a lot more radiant once it gets an oxidised surface. About 0.8) Ceramic Zirconia on steel has an emissivity of around 0.5 So, fibreglass makes even stainless steel a BETTER radiator of heat. It does nothing to keep heat away from anything else, but makes it worse! And a ceramic coating on stainless is a waste of money. It makes mild steel a much better radiator, althogh what it really does is protect it from rusting. So, for best value, a stainless manifold, and leave it naked! John Thanks John This would be easier and cheaper so gets my vote. I don't like to go too far with the wrap and change it periodically in case it gets all oily and flammable. Interesting stuff... Quote Link to post Share on other sites
Fireman049 Posted February 19, 2016 Report Share Posted February 19, 2016 Hi Mark ~ Your set-up is the perfect solution. Very similar to the Austin Healey cold air box for the '100'M. (LeMans). Unfortunately there is no room for such a set-up on a 3A otherwise I'd readily install it! Tom. Quote Link to post Share on other sites
McMuttley Posted February 19, 2016 Report Share Posted February 19, 2016 I've said before how sceptical I am about this subject, for two reasons. So, for best value, a stainless manifold, and leave it naked! John Music to my YORKSHIRE ears, but that thermal or financial value John ? Quote Link to post Share on other sites
Mark1965TR4aBRG Posted February 19, 2016 Report Share Posted February 19, 2016 Hi Mark ~ Your set-up is the perfect solution. Very similar to the Austin Healey cold air box for the '100'M. (LeMans). Unfortunately there is no room for such a set-up on a 3A otherwise I'd readily install it! Tom. Thanks Tom I'm hoping it's the optimum solution - taken a bit of engineering so far but all good fun!! Quote Link to post Share on other sites
RobH Posted February 19, 2016 Report Share Posted February 19, 2016 'So, fibreglass makes even stainless steel a BETTER radiator of heat. It does nothing to keep heat away from anything else, but makes it worse! ' John - the outer layer of fibreglass may be a better radiator of heat than bare stainless but the heat has to get to the outer surface first. That is mainly through conduction, not radiation and the entrapped air also helps to make a woven layer of FG a much worse conductor of heat - so no it does not make things worse, it makes them considerably better. The thermal conductivity of glass is about 0.8W/mK whereas that of steel is about 43W/mK. Since the emissivities you quoted are in the ratio of 0.75 to 0.59 it makes a bare stainess manifold 43/0.8 x 0.59/0.75 or around 40 times worse. (Yes I know that is a very simplistic calculation but it gives the gist of it.) Rob Quote Link to post Share on other sites
McMuttley Posted February 20, 2016 Report Share Posted February 20, 2016 or there is gold ! Quote Link to post Share on other sites
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