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c.ruber Samba Member
Joined: January 23, 2005 Posts: 634 Location: Mid TN
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Posted: Thu Aug 14, 2014 8:50 am Post subject: Paint the cylinders? |
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I recently removed my P&Cs for a hone and re-ring. The machine shop glass beaded the exterior of the cylinders and I think I remember reading in the "How to hot rod your VW" book that a high temp black paint can be applied to the outside of the cylinders. What's your take? Rust or black paint? _________________ ...and progress is not intelligently planned... |
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Glenn Mr. 010
Joined: December 25, 2001 Posts: 76760 Location: Sneaking up behind you
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Posted: Thu Aug 14, 2014 9:23 am Post subject: |
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A thin coat of BBQ paint.
_________________ Glenn
74 Beetle Specs | 74 Beetle Restoration | 2180cc Engine
"You may not get what you pay for, but you always pay for what you get"
Member #1009
#BlueSquare
Last edited by Glenn on Thu Aug 14, 2014 9:24 am; edited 1 time in total |
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smkn_vw Samba Member
Joined: August 22, 2004 Posts: 809
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Posted: Thu Aug 14, 2014 9:24 am Post subject: |
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Paint black just a thin coat is all you need rust looks nasty on cylinders and only gets worse. I washed mine using a dish washing bristle brush, warm water, and simple green and dried immediately with air compressor. Prepped and painted thin coat of satin black heat paint. Mine were brand new Mahle's so was best time to do it without rust. They're holding out well and everytime I'm under the car and see them i'm so glad I made the extra effort to paint them. _________________ "So didja?" -Bob Hoover |
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sloboatnova Samba Member
Joined: September 20, 2009 Posts: 989 Location: Broken Arrow, Ok
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raygreenwood Samba Member
Joined: November 24, 2008 Posts: 21474 Location: Oklahoma City
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Posted: Thu Aug 14, 2014 10:34 am Post subject: |
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sloboatnova wrote: |
Agreed. I painted mine on the 1915 I'm building. Don't use any paint that has ceramic in it. |
Perfectly put....not to get too deep into this again for the 100th time....but ceramic based or very heavy metal based high temp paints or epoxies (most of which will not handle the heat) will actually hold in heat.
If you can find a flat or satin enamel...its even better than gloss.
The VHT brand engine enamels and metallics...which I dearly love for many parts...are a no-no on the cylinders. Too much metal flake and heat holding capacity.
The basic rustolium high temp barbecue paint which is largely carbon black for a pigment....does really well.
If you can find some in non-aerosol and thin it with about 10-15% Xylene ...no more...then it works even better with two very thin coats. Ray |
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Humdinger Samba Member
Joined: September 27, 2012 Posts: 183 Location: NE Arkansas
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Posted: Thu Aug 14, 2014 9:35 pm Post subject: |
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I asked a friend of mine this same question a couple of weeks ago while at his shop. He races vw's and when i asked him he told me to look under the apron of his drag bug. I saw the cylinder fins were a nice flat/satin black. When i asked him what he used he showed me a cheap spray can of regular flat black paint (not hi temp, bbq, or ceramic) from NAPA and said he sprayed them a long time ago and never had rust problems! Apparently those cylinders don't get hot enough to burn it off so i painted mine with a similar paint night before last. |
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Vanapplebomb Samba Member
Joined: November 03, 2010 Posts: 5389 Location: Holland, MI
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Posted: Fri Aug 15, 2014 8:40 am Post subject: |
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Interesting. It looks nice, but is rust really going to hurt the cylinders any? I just cant see a little rust being any sort of issue, threatening the integrity of the cylinders. _________________ 1800 Type 4 Berrien 295
http://www.thesamba.com/vw/forum/viewtopic.php?t=487021 |
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smkn_vw Samba Member
Joined: August 22, 2004 Posts: 809
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Posted: Fri Aug 15, 2014 8:49 am Post subject: |
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Rust won't hurt but painting just gives a cleaner look. If anything, over time the smoother painted finish will allow smooth air flow by not catching and trapping dust and dirt as easy but then this is getting too OCD. _________________ "So didja?" -Bob Hoover |
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raygreenwood Samba Member
Joined: November 24, 2008 Posts: 21474 Location: Oklahoma City
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Posted: Fri Aug 15, 2014 9:39 am Post subject: |
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Vanapplebomb wrote: |
Interesting. It looks nice, but is rust really going to hurt the cylinders any? I just cant see a little rust being any sort of issue, threatening the integrity of the cylinders. |
Mmmm.....I dont really want to get into this here. Too many people don't understand the physics involved and I have to keep explaining it.
Suffice to say there are several very long threads on the STF and maybe here as well...where I detailed a fairly involved series of tests I did back around 1999-2000 on cylinders, cylinder coatings and steel and aluminum plates with different coatings and colors.
I deal with coatings and color and a lot of chemicals for a living. Back then I had time and worked for several companies with very good labs and equipment.
I will keep it simple and as short as I can.
The rust will not "hurt" the cylinder. However....rust has very high, rough surface area, is an airflow drag....and its an insulator. Its not a huge issue...but it means about 15-20*F of extra cylinder temp I found in testing...that you could be getting rid of.....and yes...I had very controlled tests and atmospheres when I tested so I know this is fact.
So there is a a minor but OK reason to bead blast or soda blast the outside if yours are crusty before you paint them.....or better yet, clean them before they rust and then paint them.
The gist with the paint and color....is that the paint should have as few insulating properties as possible (metallics or ceramics or mineral based flow additives like talc).
The point is that you have constant heat being created inside of the cylinder, conducting into the cast iron cylinder and you want nothing impeding it from radiating off the outside surfaces.
The other factor....and here we go....is that black surfaces attract heat......and that is actually a misnomer.
Precisely put....black surfaces lack the ability to reflect away the heat directed at it from any source (radiant, conducted or convection). White light contains the entire spectrum including infrared as heat. Short of a mirror....a white glossy surface absorbs less heat because its capable of reflecting back virtually the entire spectrum.
Thats WHY the surface is visibly seen as white....because its reflecting back to the eye the entire spectrum of white light.
Precisely put...the colorimetric definition of black is the total absence of spectral color. It reflects outward...no color wavelengths of light. It absorbs them all including infrared as heat.
Light carries all of the spectrum including infrared which is heat energy. Infrared energy...heat....is light because it gives off photons....which is why heat is seen as a glow...or light throw infrared optics. Most people don't understand that...and this is where it usually turns into a "you are full of shit session".....I do this for a living people.
A gloss black surface coating of the same material next to a matte black surface under the same heat source can stay upwards to 25-30% cooler because spectral gloss reflects away a large portion of the infrared spectrum and a chunk of the UV that is quickly converted upon absorption...into heat.
Perversely....this process works kind of inversely inversely as well to a moderate amount. The black coating...even though it is thin....is three dimensional. It exists. You cant just think of it one dimensionally by telling yourself...."its just a color"
As the cast iron conducts heat to its outer BLACK surface....part of that heat is radiated away even regardless of cooling air as photons in the infrared range. Invisible...but heat nonetheless.
A gloss coating simply bounces the radiated photons back and forth between the gloss surfaces of the fins. So this should be good right?...because at least they are not absorbing...right?
Well...no..because as they get bounced back and forth they will sooner or later be absorbed. And while the photons are bouncing back and forth...they are not getting taken away by cooling air....and remember....THIS IS A CONSTANT HEAT SOURCE. The cylinder is not waiting for your last batch of photons and electrons to dissipate. It is constantly adding more.
Radiated photons will not be affected by cooling air going through these fins.
A matte black surface traps stray radiant heat at the surface where the cooling air can pull it away.
Thats the best explanation that more than a handful of people with physics and chemistry in their background could offer who watched me working with this back in 1999.......because.....as noted....its an easy concept to get and prove... the 15-20* heat shed ability of no rust versus black paint....but we saw a further fairly constant 20-25*F difference between gloss and matte surfaces.
So...getting rid of the rust and putting on a thin coat of matte black....can shed about 35-45*F of heat.....that's not bad for something that also looks good.
But wrap your head around this....its what is at the root of arguments between many who don't really have a grasp of color theory and color physics or sometimes physics in general...whenever this question comes up and we start talking about it.
This does not mean that your cylinders will just constantly now run 35-45* cooler. They "can".....but in general the matte black cylinders will be just a bit slower to reach nominal running temperature and will reach pretty much the same running temps they always do..........BUT they will have less over temp heat spikes ...which is key.
The matte black coating simply gives the cylinders the ability to more efficiently shed "X" amount more BTU's per second at a constant rate....than they have with just matte rust or gloss black.
We found in the test cylinder that with the matte black coating we could add in just a bit more heat energy and still maintain the normal cylinder temp baseline without increasing the cooling air volume or dropping the cooling air temperature.
Sorry for the length. Ray |
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Eaallred Samba Member
Joined: May 18, 2003 Posts: 5756 Location: West Valley City, Utah
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Posted: Fri Aug 15, 2014 9:56 am Post subject: |
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Cheap black paint here too. I like satin black over flat black only because it is easier to clean come rebuild time. Gloss black works fine too, but not as much dissipation.
Bob Hoover would thin down black paint and brush it on. Probably the best way, but possibly overkill.
Agree with the above, never use a "High Temp" paint, as it is designed to somewhat insulate (most have ceramic in them). Just a step backward is all that is. Don't need high temp paint anyway as the cheapest of the cheap paints don't burn off cylinders. I've burnt paint off brake drums, and never off cylinders. Think about that! lol _________________ Eric Allred
You have to remember something: Everybody pities the weak; Jealousy you have to earn. |
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Juanito84 Samba Member
Joined: March 17, 2012 Posts: 2436 Location: Colorado Mountains
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Posted: Fri Aug 15, 2014 1:35 pm Post subject: |
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raygreenwood wrote: |
Vanapplebomb wrote: |
Interesting. It looks nice, but is rust really going to hurt the cylinders any? I just cant see a little rust being any sort of issue, threatening the integrity of the cylinders. |
Mmmm.....I dont really want to get into this here. Too many people don't understand the physics involved and I have to keep explaining it.
Suffice to say there are several very long threads on the STF and maybe here as well...where I detailed a fairly involved series of tests I did back around 1999-2000 on cylinders, cylinder coatings and steel and aluminum plates with different coatings and colors.
I deal with coatings and color and a lot of chemicals for a living. Back then I had time and worked for several companies with very good labs and equipment.
I will keep it simple and as short as I can.
The rust will not "hurt" the cylinder. However....rust has very high, rough surface area, is an airflow drag....and its an insulator. Its not a huge issue...but it means about 15-20*F of extra cylinder temp I found in testing...that you could be getting rid of.....and yes...I had very controlled tests and atmospheres when I tested so I know this is fact.
So there is a a minor but OK reason to bead blast or soda blast the outside if yours are crusty before you paint them.....or better yet, clean them before they rust and then paint them.
The gist with the paint and color....is that the paint should have as few insulating properties as possible (metallics or ceramics or mineral based flow additives like talc).
The point is that you have constant heat being created inside of the cylinder, conducting into the cast iron cylinder and you want nothing impeding it from radiating off the outside surfaces.
The other factor....and here we go....is that black surfaces attract heat......and that is actually a misnomer.
Precisely put....black surfaces lack the ability to reflect away the heat directed at it from any source (radiant, conducted or convection). White light contains the entire spectrum including infrared as heat. Short of a mirror....a white glossy surface absorbs less heat because its capable of reflecting back virtually the entire spectrum.
Thats WHY the surface is visibly seen as white....because its reflecting back to the eye the entire spectrum of white light.
Precisely put...the colorimetric definition of black is the total absence of spectral color. It reflects outward...no color wavelengths of light. It absorbs them all including infrared as heat.
Light carries all of the spectrum including infrared which is heat energy. Infrared energy...heat....is light because it gives off photons....which is why heat is seen as a glow...or light throw infrared optics. Most people don't understand that...and this is where it usually turns into a "you are full of shit session".....I do this for a living people.
A gloss black surface coating of the same material next to a matte black surface under the same heat source can stay upwards to 25-30% cooler because spectral gloss reflects away a large portion of the infrared spectrum and a chunk of the UV that is quickly converted upon absorption...into heat.
Perversely....this process works kind of inversely inversely as well to a moderate amount. The black coating...even though it is thin....is three dimensional. It exists. You cant just think of it one dimensionally by telling yourself...."its just a color"
As the cast iron conducts heat to its outer BLACK surface....part of that heat is radiated away even regardless of cooling air as photons in the infrared range. Invisible...but heat nonetheless.
A gloss coating simply bounces the radiated photons back and forth between the gloss surfaces of the fins. So this should be good right?...because at least they are not absorbing...right?
Well...no..because as they get bounced back and forth they will sooner or later be absorbed. And while the photons are bouncing back and forth...they are not getting taken away by cooling air....and remember....THIS IS A CONSTANT HEAT SOURCE. The cylinder is not waiting for your last batch of photons and electrons to dissipate. It is constantly adding more.
Radiated photons will not be affected by cooling air going through these fins.
A matte black surface traps stray radiant heat at the surface where the cooling air can pull it away.
Thats the best explanation that more than a handful of people with physics and chemistry in their background could offer who watched me working with this back in 1999.......because.....as noted....its an easy concept to get and prove... the 15-20* heat shed ability of no rust versus black paint....but we saw a further fairly constant 20-25*F difference between gloss and matte surfaces.
So...getting rid of the rust and putting on a thin coat of matte black....can shed about 35-45*F of heat.....that's not bad for something that also looks good.
But wrap your head around this....its what is at the root of arguments between many who don't really have a grasp of color theory and color physics or sometimes physics in general...whenever this question comes up and we start talking about it.
This does not mean that your cylinders will just constantly now run 35-45* cooler. They "can".....but in general the matte black cylinders will be just a bit slower to reach nominal running temperature and will reach pretty much the same running temps they always do..........BUT they will have less over temp heat spikes ...which is key.
The matte black coating simply gives the cylinders the ability to more efficiently shed "X" amount more BTU's per second at a constant rate....than they have with just matte rust or gloss black.
We found in the test cylinder that with the matte black coating we could add in just a bit more heat energy and still maintain the normal cylinder temp baseline without increasing the cooling air volume or dropping the cooling air temperature.
Sorry for the length. Ray |
Here's an example. Wood stoves are usually painted with a thin layer of flat or matte black not-too-high-temp paint because it dissipates more radiant heat.
Here's an opposite example: chrome and polished aluminum parts don't dissipate much radiant heat.
And yes, a thick layer of high temp paint will insulate the surface from the metal.
I also feel that black matte tins help because they assorb more radiant heat off the engine. _________________ If a water cooled engine cools its water with air, isn't it just an overcomplicated air cooled engine? |
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raygreenwood Samba Member
Joined: November 24, 2008 Posts: 21474 Location: Oklahoma City
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Posted: Sat Aug 16, 2014 6:27 am Post subject: |
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Yes...matte black.....on surfaces that dont really have their own constant heat source directly heating one side or the other will definately get hotter than gloss. Its because they are picking up radiant heat from other radiating surface around them...and because they are not reflective....they cannot reflect it away. Yes....they still collect heat from the engine on the inside of the tin.....but they also collect instead of reflect.....radiant heat from sources all over the engine compartment.
There are so many heat sources around engine that I have never definitively been able to measure a big difference between gloss and matte on engine tins on a working engine. Its all over the place.
But with straight steel and aluminum plates with gloss vs black with uniform one and two side heat sources......the gloss black reflects away significant amounts of heat compared to matt. Ray |
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Quokka42 Samba Member
Joined: December 02, 2010 Posts: 3117 Location: Melbourne, Australia
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Posted: Sat Aug 16, 2014 6:47 am Post subject: |
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Sorry, I really didn't want to comment on this yet again, but there is just too much bullshit here. The black of a painted surface is not the same as a physicist's black radiating body, and the cylinders are not cooled by radiated heat to any significant degree anyway.
If you live in a humid climate, or the engine will see infrequent use, paint the cylinders with a thin coat of paint. You can thin it a bit to make it matte if you like, but I really don't think the slight increase in surface area will make any difference. Seriously, if you do it right it won't matter a roo's poo what colour it is.
For the rest of us, if we have the nice rough black or grey of the cast iron the most we might do is give it a light spray with a high smoke point oil.
I apologise to the above again - maybe you're drunk, but bullshit is bullshit. _________________ There has only ever been one man who was perfect, and they nailed Him to a cross. |
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c.ruber Samba Member
Joined: January 23, 2005 Posts: 634 Location: Mid TN
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Posted: Sat Aug 16, 2014 7:17 am Post subject: |
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Thanks for all the responses. As I stated in the first post, my cylinders have been glass bead blasted. Therefore they are bare naked cast iron. When I scrub the honing grit from the inside of the cylinders with HOT water and comet, the exterior will rust in a heart beat. I don't like rust...anywhere. Whether there is a heat shedding by product or not I want to protect the exterior of the cylinders. I didn't want to start a discussion about this test or that. Thanks for the insight and what NOT to use. _________________ ...and progress is not intelligently planned... |
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EverettB Administrator
Joined: April 11, 2000 Posts: 69733 Location: Phoenix Metro
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Posted: Sat Aug 16, 2014 9:24 am Post subject: |
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Quokka42 wrote: |
If you live in a humid climate, or the engine will see infrequent use, paint the cylinders with a thin coat of paint. You can thin it a bit to make it matte if you like |
This is off the topic but a question to anyone:
Does thinning paint make it matte?
I did not think that was true. I tried to google this and everything I found said you have to add a matte agent to make shiny paint flat. Or dull it down with sandpaper, etc. _________________ How to Post Photos
Everett Barnes - [email protected] | My wanted ads
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Stop dead photo links! Post your photos to The Samba Gallery! |
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Brian Samba Moderator
Joined: May 28, 2012 Posts: 8340 Location: Oceanside
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Posted: Sat Aug 16, 2014 9:36 am Post subject: |
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EverettB wrote: |
Does thinning paint make it matte?
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I don't think so. but on a another side note if you get the right amount of thinner in your paint you create a hammertone finish. _________________ Wash your hands
'69 Bug
'68 Baja Truck
'71 Bug
'68 Camper
Only losers litter |
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Hophead Samba Member
Joined: January 03, 2005 Posts: 940 Location: Chico,Ca
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Posted: Sat Aug 16, 2014 10:20 am Post subject: |
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Thinning paint might knock the gloss down a minute amount but it will not make it "flat".
In general, paint starts out glossy and they ADD material to the paint to reduce the gloss. Many different materials are used. They are usually a powder. So which compound they use can make a difference in the insulating properties of that brand.
At least that was my experience when I used to apply industrial coatings decades ago. _________________ 70' Beetle Pan off Resto
2110cc
82 X 90.5
P&P 043 40x35.5
9.6-1 comp
FK-8
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[email protected] Samba Member
Joined: August 03, 2002 Posts: 12785 Location: Salt Lake City, Utah
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Posted: Sat Aug 16, 2014 10:49 am Post subject: |
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Plastikote Flat black is good and very inexpensive.
You don't want to use a gloss black or semi-gloss for this, they have less surface area than the flat black. Flat black will cool better on cylinders. _________________ It's just advice, do whatever you want with it!
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Juanito84 Samba Member
Joined: March 17, 2012 Posts: 2436 Location: Colorado Mountains
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Posted: Sat Aug 16, 2014 10:55 am Post subject: |
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Quokka42 wrote: |
The black of a painted surface is not the same as a physicist's black radiating body, and the cylinders are not cooled by radiated heat to any significant degree anyway.
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I beg to differ. Yes, most of the heat is rejected by convection. But as raygreenwood pointed out, the color and radiant heat dissipation does make a notable difference.
http://swaintech.com/race-coatings/race-coating-descriptions/bbe-heat-emitting-coating/
Case in point: If color didn't make that much difference, then why did VW sell most cars with black valve covers but offered chrome valve covers for artic use?
If you paint the cylinders white or chrome them and they will run hotter, period. Put your hand under them (engine off) and it will feel cool, because white radiates very little heat. Paint them black and put your hand under there and you will feel heat because black puts our more radiant heat.
As far as gloss or flat black goes I personally don't know if there's much of a difference. Most things that are designed to dissipate radiant heat are flat black, like wood stoves. But some heat shedding coatings are gloss black. What I do know is most heat dissipating paints are flat black, but actual special coatings are gloss black.
As far as fin to fin transfer, yes that does happen. But it's not a heat trap. Radiant heat dissipates at all angles. What radiant heat that hits another fin is reassorbed. What doesn't heats whatever it hits. And if that's a black tin (reason not to use white or chrome tins) then the heat is quickly dissipated there through convection. In other words radiant heat dissipation is limited by the angular surface area and not simply surface area. _________________ If a water cooled engine cools its water with air, isn't it just an overcomplicated air cooled engine? |
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DWP Samba Member
Joined: September 11, 2007 Posts: 577 Location: Pa.
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Posted: Sat Aug 16, 2014 3:01 pm Post subject: |
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I would ask the Harley Davidson shop what they use!
DWP |
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