PorscheDoc

errrrr....what is the goo that is around the AN fitting?

SeaCay

The Swedish version of JB Weld?

Duke

Exactly. This is an old trick from the hot rodders
Empirical tests show quite a differance.

Same goes for intercooler's, but everyone is so into bling that you never see a black aftermarket IC. And if you do you'd probably think "what an amateur".

The goo around the fitting is indeed the swedish version of JB Weld
Don't be scared, the fitting is tapped and everything but we put a layer of chemical metal around it to be sure it sealed.

TRP951

good to see you are making progress on this duke cant wait too see what the finished engine looks like

Dave951

Regarding color and its effects on heat dissipation, here is a interesting site. I think some of us will be surprised at the conclusion based on the comments posted thus far.

Duke

Thanks man,
regardless if one thinks I'm on the the right path or not for power, I wont be afraid of pushing this engine to the limit and that should be interesting for the whole 951-community.

But whatever you do, there's always going to be someone faster or more extreme.
But as long as I can trap 200+ km/h and do the 100-200 km/h sprint in 7.x I know I'll be able to whop most of the cars out there.

Duke

That's interesting. But I have facts that prove otherwise. Well...as long as it doesn't get worse I guess I'm fine...and hey it looks good too!

I will post some facts from a very good engine tuning book later tonight.
Also fram what I've heard, the paint will mostly affect oil temps. But fluid as fluid..

Dave951

Duke, is the paint you used some special type of coating? If so, do you have any additional information about it (Like a spec sheet or a website link)?

Worst case scenario like you said, if it doesn't make it any worse then at least it looks sexy.

tedesco

I have got some reservations about painting as well. If you paint one engine black and another green I can understand that the black engine might run slightly colder but I still think that a NOT painted engine will be superior to both. Normally the heat conduction of paint is very poor and allthough black paint is transparent to infra red light convection of heat is penaltised. No paint (just nothing at all) is for sure the most transparent you can have and also allows direct convection between alu block and air without any barrier. So I am convinced that no paint is best for cooling. If you desperatly want to paint an engine than it might be adviseable to paint it black just to limit the damage. I really don´t see the need for painting. We don´t have iron blocks...

Duke

I suspected this would cause some different opinions
From what I know, the best color is supposed to a black subdued color for this purpose.
High gloss finish and powder coatings trap the heat in.

Laust Pedersen

Duke, with lots of power and no balance shafts you definitely will be among the “movers and shakers”


However interesting and good arguments there are in that reference, it amounts to nothing more than “hand-waving”. The fact remains that there are two heat transfer mechanisms between two media to consider, conduction (with convection) and radiation. How much each contributes under realistic circumstances determines the relevance of trying to enhance the radiation.

There is no doubt that black will enhance the radiation (black vs. white car in the sun), but the paint will also act as a thermal barrier, so it would be reasonable to assume that paint (or anodization) thickness plays an important role too.

Some time ago I got a new radiator in my BMW and contrary to the original one it was now painted black. Why would BMW add another process (cost) if it wasn’t functional?

Until having seen opposing empirical data I believe in a thin black layer to enhance heat transfer, but only between two media with a significant temperature difference.

Laust

Dave951

You claim that black paint would be hotter than a identical white one [As per you example of a car in the sun]. Then I should be able to conclude from that holding all else constant leaving the black engine block in the sun would be hotter than one coated in white paint. That being said convection depends directly on the difference between the fluid and surface temperatures. So if the surface temperature has become hotter, and the fluid has remained constant the result would seem to be obvious. It's also generally said that when conduction and/or convection is combined with radiative heat transfer (on an opaque surface), that the interaction is considered only to occur at the surface.

Some information cited from Thermal Radiation Heat Transfer: Vol 3. Which can be viewed here

I found a scholarly article on the subject, however I cannot view it. If anyone has access to Engineering Village the article is titled "The Effect of Paint Coating on Heat Transfer" Access #: 87070102810

Laust Pedersen

Correct.

Please stay clear on the terms. Conduction and convection are two different heat transfer mechanisms. Convection moves calories from one place to another through mass transfer. Wikipedia is quite good at defining those terms: http://en.wikipedia.org/wiki/Heat_transfer

The sun on a black or white car analogy is an extreme analogy since the sun is 100% radiation.

Your reference seems to be able to quantify the conduction and radiation relationships in chapter 10, but too bad you have to buy the book to get the full chapter. As you can see a rigorous theoretical analysis is no simple matter and perhaps some empirical data based on a common sense setup would answer the question of the value of black paint to enhance heat transfer.

Laust

tedesco

The facts remain: My engine is water cooled but I did not try replacing the water by paint jet maybe than the black works better

If you talk about convection please remember that there is natural- and artificial (forced) convection as well. There is quite a fresh briese in the engine bay which aids cooling. To get the most of it you primarily need good conduction due to NOT painting the block. Forget all the radiation. The engine is too cold for that (we are not talking about electronic tubes) and the radiation would only heat up other maybe more important components in the engine bay like the intake mani if it would work.

OZ951

These comments are wrong. The emissivity of aluminium is around 0.3 or something like that (depending on surface condition). If you paint it the emissivity will be around 0.9. The paint colour doesnt matter all that much and surprisingly whites can even give better results than black due to factors of reflectivity as well as emissivity. So painting the block does allow it to radiate more heat.