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are the carb heat shields worth it?

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If I can stick my nose in here for a bit. Having a carb heat shield painted black should not affect its performance to any real measureable degree. Just as polishing your intake manifold to a mirror finish will not really reflect heat from your exhaust. Stainless steel pieces often stay bare simply becasue there is no need to protect the steel from rusting with paint. Your trying to stop radiating heat, not visible light rays. Coating your manifold with a heat resistant coating would on the other hand work very well. Its a whole different type of heat to deal with than solar radiation. Infra-red temperature readers can occasionaly be fooled by shiny stuff though.

If you were running around with a glass/plexi bonnet and the dark colors were absorbing more light/solar rays than the lighter or shiny stuff you might be onto something.

Now, if I can be proven wrong on any of the above I will gladly retract my statement. But for now, I will stand by my opinion that shiny engine accessories/parts are not 'shiny' for performance reasons but purely for appearance reasons. Not that there is anything wrong with that. /bcforum/images/%%GRAEMLIN_URL%%/wink.gif
 
swift6 said:
Infra-red temperature readers can occasionaly be fooled by shiny stuff though.

If you were running around with a glass/plexi bonnet and the dark colors were absorbing more light/solar rays than the lighter or shiny stuff you might be onto something.
Click to expand...

Infra-red is part of the light spectrum but we cannot see it. It has the same physical behavior as visible light.
The reason why infra-red temperature readers are fooled by shiny objects is because they radiate less infra-red so shiny objects are doomed to transfer their heat by convection and other ways. And this works the other way round. Shiny objects absorb less infra-red radiation and so they stay cooler if there is a distance to the emitting source.

Simple test....have two cars....on in silver color, one in black. The black car is much warmer inside than the silver one.

For the same reason the NASA probes are covered with silver or gold foil.

Another thing....you can't cut a mirror with a laser beam.

That's why engines, radiators are painted (black**)...to get writ of the heat...they radiate more.

**For emitting you can chose any color you like. But for absorbing and emitting a dark color is the best.

Stefan-Bolzmann law

Edit:
I am a civil engineer an part of my job is to plan heating system to bring energy cost down.
My favorite part of the job is to rise the efficiency of very old houses which can't be isolated because of their old time status.
So I insert copper tubes into the wall. Shiny copper does emit 15% of the inside warmth through radiation. If I cover the tubes with paint or roughcast the radiation rises to 96%.
So if you paint the header it will transfer more heat to the carbs than a shiny stainless steel tube.
 
But your intake manifold is aluminum and more likely to transfer heat straight through it than reflect it. Much as aluminum foil would.

The car example would be more dependent on a greenhouse effect from glass surface area and interior color, and since dark cars tend to have darker interiors and light cars lighter interiors, its not just the exterior color that warms the car on the inside. However, the black one would be warmer to the touch from absorbing more radiation than it reflects.

I know infra red is part of the light (technically electromagnetic) spectrum. The near infra red (microscopic and closest to visible light) are not hot while far infra red (larger and closer to the microwave region of the electromagnetic spectrum) are thermal waves (hot). But also remember that under the bonnet you are also dealing with heat transfer from convection and conduction, not just radiation.

The real interesting thing here is that this discussion has spurred me to do a little more investigating... The far infra red waves (the thermal waves) carry what we call heat. From the sun, from fires, from raiators etc... The larger particles of the far waves allow us to seem them occasionally, or at least the distortion that they can cause. Silver colored and specifically aluminum materials are not very efficient at reflecting these far infra red waves (though they are very efficient at reflecting visible light and near infra red rays). The reason why NASA craft destined to be in space for long periods (according to NASA) are covered primarily in gold foil externally is because the gold foil (a metallized mylar) is more efficient at reflecting the far infra red waves while less efficient at reflecting visible light waves. The gold foil on space craft (usually pointed at the sun) is used to help regulate the internal temperatures of spacecraft and are coupled with black radiating panels that are aimed torwards dark (cold) space. Silver foil is used for other reflective duties and not heat management. Its also why astronaut helmets have a gold coatings on their visors, to keep the helmets from getting too hot inside.

While I understand that Black objects do radiate more efficiently, my point with Dale's carb shield is that in his situation, the color of his carb shield is most likely not going to be that critical in its function as it is probably more of a form over function item as are most heat shields on stock TR's.

As for the copper tube example. I am wondering if that increased radiation after painting and/or specifically roughcast has to do with the increased surface area over the smoother/smaller surface area of the straight copper tube.

One of the reasons that headers produce more heat under the hood than a stock manifold on the same engine is the increased surface area. They heat up quicker because of the thinner material. If you coat the header with a thermal ceramic coating it will radiate less heat.

So, would this mean that there could be call for gold plated bling under the hood to be more heat efficient than chrome plated bling? /bcforum/images/%%GRAEMLIN_URL%%/wink.gif
 
You are very close to be correct.
Gold foil is used because the density of gold is high and so a very thin layer of gold is more efficient to far infra-red than any other stuff.

If we are talking about compact materials like a sheet metal the Kirchoff radiation rule says that the absorption is equal to the emission.
If you follow this the absorption grade of i.e. aluminium is e = 0.04 so the emission is 0.04 and the sheet stays colder.

If you paint the sheet metal black the absorption gets close the 0,98 and so the emission is 0,98.

If you have a hot heat shield mounted to the carbs that won't be a good thing, right?

So with my outside polished intake header I have close to no absorption of radiation from the header, only conduction from the head and convection from hot air from the header.

If the exhaust header is polished then he will radiate very small amounts of heat...e=0,06...0,2.
If it is painted then it will radiate 0.85 or more.
A complete different thing is if the header is coated with an insulation like wrap strap. This will bring down the convection and it will half the radiation (something like that).

But to come back to heat shields....a black one would'n work that good as a polished one does.

I'm sorry that I'm not able to explain better but I'm a German and I try my very best.
 
swift6 said:
The car example would be more dependent on a greenhouse effect from glass surface area and interior color, and since dark cars tend to have darker interiors and light cars lighter interiors, its not just the exterior color that warms the car on the inside. However, the black one would be warmer to the touch from absorbing more radiation than it reflects.
Click to expand...

A better example....

An open Triumph with white leather seats and one with black leather seats.
Both outside in the sun.

Out of which one would you jump if you sit in naked?

/bcforum/images/%%GRAEMLIN_URL%%/wink.gif
 
/bcforum/images/%%GRAEMLIN_URL%%/lol.gif Nice one Peter!

Christian, your English is good enough to get your points across. Probably better than you think it is. Don't worry about that, plus, the more you use it, the better it will get. At least that has been my experience.

Also, I didn't mean to imply that Dale would see any benefit from having a black heat shield. Just that in his application he probably won't see that much of a detriment. His drives are currently fairly short after all.
 
swift6 said:
Christian, your English is good enough to get your points across. Probably better than you think it is. Don't worry about that, plus, the more you use it, the better it will get. At least that has been my experience.
Click to expand...

Thanks for that!

About the black shield:

As a very famous Triumphist said: One valid test tell more than 10000 expert opinions.

So the best is, to try out and see what happens.
 
Well it looks like I will be adding the heatshields after all.

I was going to take off the headers and get them painted, but after getting them removed from the head, I couldn't get the union pipe off the end of them. Which means that I can't take them out of the car.

So in the interest of being able to use the car this summer, I am going to put the headers back on as they are, put on the heat shield and enjoy the car for the summer.

The exhuast can go on my winter project list.
 
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