Effectiveness of ceramic coating
Discussion
Temps fluctuate a lot so it's very difficult to have comparable 'test' results. I did take some comparative measurements ranging laser thermometer across parts of manifold after doing a hot run up & down dronfield bypass & pulling straight into BK/LC.. & then cooled down tickover at home. Can't remember the exact results but they were pretty astounding, and probably a little corrupted since I removed the pre-cats when swapping to coated manifolds... I did concentrate on the bends opposite the exhaust ports, which seemed to be the hottest areas, difficult to scan the rest of the manifolds/Y as they are cooling so quickly...
I am planning on getting mine cermachromed for that exact reason, well that and the fact they look pretty. 
I know Quinny and a few others on here have had it done. This thread may be of interet to you:
http://www.pistonheads.com/gassing/topic.asp?h=0&a...
I know Quinny and a few others on here have had it done. This thread may be of interet to you:
http://www.pistonheads.com/gassing/topic.asp?h=0&a...
dnb said:
Has anyone tested how well ceramic coating an exhaust keeps the heat in? I have a number of options to solve the problem of excessive under bonnet temperatures (usually while going slowly), and ceramic coating is the easiest assuming it will work!
Thanks.
Well, I dunno that it is the easiest option; why not bandage your pipework? You can do that in situ and it'll cost you about £30. Why not try that first to see if it helps your situation?Thanks.
I have had pipes ceramic coated (inside and out) and I cannot verify how effective it was from carrying out any experimentation. I'm just not as convinced as some about it; it aint that thick a coat. You'll burn your hands on a ceramic teapot and that's pretty darned thick by comparison. It can look nice though and provides a barrier to keep your tubes corrosion free if you have deep pockets. I know there are DIY kits too if you have a blast cabinet for the prep' and a suitably sized oven for the bake.
I have to agree with you Bruce. I'm not convinced yet about performance, which is why I was asking the question. No doubt it looks nice, but that's not the point. I don't drink tea, so I have so far avoided ceramic teapots!
I was trying to avoid exhaust bandage - It isn't compatible with my hands.
I was trying to avoid exhaust bandage - It isn't compatible with my hands.
One advantage that seems to have come out from discussions on these boards over the years of bandage 'v' coating is the application of bandage often results in cracked manifolds, it happened to me on my previous TVR and it's why I don't use the bandage now.
I think the summation of lots of discussion seems to be that applying the bandage has to be done very very carefully as where it is uneven you get differing points of cooling. Namely where one area may cool quicker than another as it's only got one wrap, versus an overlap for example.
When the manifold cools, the differing cooling rates cause the cracking.
Coating 'may' overcome this by applying a more even coat of heat resistant material allowing the manifold to cool at a much more consistent rate minimising the cracking issues, which I haven't heard of so much with ceramic coated manifolds as I have with bandaged ones . .
The other issue with bandage is that it does attract condensation, which if you have SS manifolds is not so much of an issue, but where you may have less high quality SS or mild then potentially this could encourage corrosion.
I'm still on my original TVR manifolds minus all the CAT's and at 85k miles they're still going strong, they are not bandaged of coated. If I had to choose I would go for coated over bandaging due to preivous experience of cracking and that the bandage does break down over time and can become brittle, even the expensive stuff.
I think the summation of lots of discussion seems to be that applying the bandage has to be done very very carefully as where it is uneven you get differing points of cooling. Namely where one area may cool quicker than another as it's only got one wrap, versus an overlap for example.
When the manifold cools, the differing cooling rates cause the cracking.
Coating 'may' overcome this by applying a more even coat of heat resistant material allowing the manifold to cool at a much more consistent rate minimising the cracking issues, which I haven't heard of so much with ceramic coated manifolds as I have with bandaged ones . .
The other issue with bandage is that it does attract condensation, which if you have SS manifolds is not so much of an issue, but where you may have less high quality SS or mild then potentially this could encourage corrosion.
I'm still on my original TVR manifolds minus all the CAT's and at 85k miles they're still going strong, they are not bandaged of coated. If I had to choose I would go for coated over bandaging due to preivous experience of cracking and that the bandage does break down over time and can become brittle, even the expensive stuff.
Was chatting to one of the thermal guys at work and took a look at the thermal emisivity(sp?) of different material at a particular temperature in one of his reference books. The only this that shone out with a lower figure at these temperatures was polished metal. Painted coatings make a difference at solar type temperatures (a few thousand C and upwards) but not at a few hundred C that we see on exhausts.
We could only conclude from this that the ceramic coatings must be acting as an insulator as it seems pretty unlikely that their emsivity(sp?) will be that good at the temperatures we are talking about although we don't have figures for the type of coating we are talking abotu here.
We could only conclude from this that the ceramic coatings must be acting as an insulator as it seems pretty unlikely that their emsivity(sp?) will be that good at the temperatures we are talking about although we don't have figures for the type of coating we are talking abotu here.
Thanks Rob. That lines up with the conclusion from a discussion at work.
The problematic heat from the exhausts is from IR spectrum radiation (isn't it?) Conduction is probably not worth worrying about.
Exhaust wrap is not a particularly sane way to deal with radiation. It will slow down the heat transfer from exhaust to intake manifolds, but it will also slow down the return to "normal" temperatures once there is airflow through the engine bay. So the nature of the problem has merely been changed.
A ceramic coating (assuming it is a good blocker of IR radiation) will serve to make the exhaust gas hotter. While this would be really good in a turbocharged car (more energy to drive the turbo), it seems it might not work at all in a NA car besides a little more gas velocity in the exhaust. Having a guess at the emissivity of steel as 0.85 and ceramic as 0.69, a small rise in gas temperature conducting into the exhaust quickly means the exhaust raidiates the same energy as before. So not a solution my heatsoak problem, but may give a little more power?
So this leads to the idea of a highly polished steel heat shield with air gap between it and the exhaust, and some thin insulator bonded to the top surface to stop reduce convection arranged such that the air between shield and exhaust is purged when the car is in motion. Again, not a true solution to heat soak since (there actually isn't a complete solution as far as I can see) the heat can still build up over time, but it looks like the best so far.
Please let me know what's wrong with my logic.
The problematic heat from the exhausts is from IR spectrum radiation (isn't it?) Conduction is probably not worth worrying about.
Exhaust wrap is not a particularly sane way to deal with radiation. It will slow down the heat transfer from exhaust to intake manifolds, but it will also slow down the return to "normal" temperatures once there is airflow through the engine bay. So the nature of the problem has merely been changed.
A ceramic coating (assuming it is a good blocker of IR radiation) will serve to make the exhaust gas hotter. While this would be really good in a turbocharged car (more energy to drive the turbo), it seems it might not work at all in a NA car besides a little more gas velocity in the exhaust. Having a guess at the emissivity of steel as 0.85 and ceramic as 0.69, a small rise in gas temperature conducting into the exhaust quickly means the exhaust raidiates the same energy as before. So not a solution my heatsoak problem, but may give a little more power?
So this leads to the idea of a highly polished steel heat shield with air gap between it and the exhaust, and some thin insulator bonded to the top surface to stop reduce convection arranged such that the air between shield and exhaust is purged when the car is in motion. Again, not a true solution to heat soak since (there actually isn't a complete solution as far as I can see) the heat can still build up over time, but it looks like the best so far.
Please let me know what's wrong with my logic.
dnb said:
Please let me know what's wrong with my logic.
A shiny piece of steel is going to be heavy and heavy is bad. Not going slowly would be my suggestion 
(though this may require moving to a part of the world with more roads and less cars on them)I may be going (even more) mad but didn't you ceramic coat yours ages ago?
I am about to commit a mortal sin. My 1992 4.3 Pre cat has had it's origionality spoilt by the need for a suspension rebuild, and following that I've decided to replace the tatty air flow ducting for ACT smooth bore. As I need to replace a water hose I'm also using ACT silicone hoses. I am currently considering ceramic coating of the manifolds and Y piece and a vented bonnet from Fibreon to reduce the engine created heat. Do people think one or the other or both of ceramic coating or vented bonet will be best? I know origionality is preferable but proper powder coating on wishbones etc. during suspension rebuild has meant tat my car is no longer 'origional' apart from service items, but I can live with all of that as we must move on.
You're thinking of the Impreza manifolds. I only coated a couple of parts of the Griff exhaust where it passed close to things intolerent to heat (PAS pipes etc).
I was thinking of very thin steel to keep the weight down.
Sorry Daggsy - no idea what would be best yet, but I am considering a heat shield to "duct" the hotness out of some vents...
I was thinking of very thin steel to keep the weight down.
Sorry Daggsy - no idea what would be best yet, but I am considering a heat shield to "duct" the hotness out of some vents...
rev-erend said:
Must admit that I had my exhausts coated but have also bought bandage and plan to use that where the exhaust passes very close to vital parts like the engine mounts and starter motor and for the most part people looking at the engine will be unaware of the bandage.
Rev, are you planning to bandage a ceramic coated length of exhaust? Beware, I did this and it caused the coating to crumble from the pipework. I couldn't think of a reason why I shouldn't reduce the radiated heat further by doing this but before I went ahead I asked the question of those I considered knowledgeable. No one came up with reason why it shouldn't be done so I went ahead to my cost. The tubes were recoated but they should now come with a warning label along the lines of 'DO NOT BANDAGE THIS ITEM'.Gassing Station | Griffith | Top of Page | What's New | My Stuff