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Black Motors vs. Natural Aluminum

  • Thread starter Thread starter JMHJ
  • Start date Start date
bonanzadave said:
There seems to be as much conjecture in the heat sink world as there is in the GS motor world as far as color is concerned............

"Radiative heat transfer (heat transfer by electromagnetic radiation) is proportional to
e*(T1^4 - T2^4)
Click to expand...
So the question is how much heat is actually removed by radiation as opposed to convection?

Couple assumptions 300F engine, 70F air temp
Black engine Emissivity 0.90
Coefficient of convection 100 w/m^2*K (high value for air)

Radiation 1,221 watts
Convection 12,700 watts

So radiation might account for 10% of your engines cooling. The cooler the engine the smaller the role, the hotter the engine the larger the possible role of the radiation.

More importantly the engine would have to run approximately 25F hotter for the convection to more than make up for no effective radiation.
 
Which one sheds water better? Just kidding. :o

Thanks for the informative replies. I was wondering regarding a special HVAC application. Some outdoor AC units have black coil fins, which would fit with the black cools better scenario (even if just a little bit).

Radiant heat barriers installed near the underside of a roof having the reflective side down doesn't make intuitive sense either.
 
Aw, you guys have gotta be kidding me:-$

Mysuzyq said:
Here's one theory on why black paint enhances cooling.....others argue that white has higher heat emissivity, and black really isn't black in the IR spectrum, so draw your own conclusions. It's safe to say that the difference is temps is small enough to be insignificant, so go with whatever floats your boat cosmetically.;)
Click to expand...

It's got to be cosmetic (and I do agree that black does look cool....which is not to say silver does NOT look cool as well). As well as insignificant. Why bother to paint the engine/engine cases on a full faired bike such as a GSX-R or a Ducati? You can't see 'em so, are they painted?

It is well established that black absorbs heat and silver/white/light reflects heat (otherwise windshield "shades" would be black vs silver) BUT what if the "heat" is coming from "inside the car" if you will. Well in that case I vote for black since you obviously don't want to "reflect" the heat back to where it came from.

BUT BUT BUT this is all theory. Anyone claiming black engines cool better whatever, I want to see some proof. On a watercooled (or oil-cooled like gsx-r) bike, who cares? The thermostat will dictate when to cool and regulate temps. A few degrees one way or another - assuming this is even the case - due to black or not engine paint won't make one dang bit of difference, the thermostat keeps it at rated temp.

On an air-cooled motor, well, "maybe". However, I look at my current '96 porsche 911 air/oil cooled motor, which exactly like my old '79 porsche 911 air/oil cooled motor is NOT painted. If this was such an easy thing to do and makes such a "huge" difference, don't you think Dr. Porsche would have employed this? And the esthetics of the motor don't come into play like a bike since you can't see sh** on the motor? And they built this motor for over 40 years ('66 - '98). Think about it guys!:hand::hand: I think not.
 
If there were a problem with cooling, wouldn't they have used bigger cooling fins?
Paint them purple with green polka dots, it just doesn't matter..
 
Now, purple dots, might be over the edge. :lol:

I'd say, just tune the bike till the plugs run a medium to dark black, sort of a burnt toast color, it should run cool enough then, and just carry some spare plugs. That's what I do... :p
 
andrewpogany said:
Aw, you guys have gotta be kidding me...

On an air-cooled motor, well, "maybe". However, I look at my current '96 porsche 911 air/oil cooled motor, which exactly like my old '79 porsche 911 air/oil cooled motor is NOT painted. If this was such an easy thing to do and makes such a "huge" difference, don't you think Dr. Porsche would have employed this? And the esthetics of the motor don't come into play like a bike since you can't see sh** on the motor? And they built this motor for over 40 years ('66 - '98). Think about it guys!:hand::hand: I think not.
Click to expand...

I don't think there's any argument here, Andrew.. nobody said it made a huge difference. I think I mentioned in the same post you quoted, or another, the fact that our air cooled engines aren't very reliant on radiation for cooling; most of it takes place via (forced) convection (the movement of cooler air over the engine). Not very familiar with the Porsche's cooling system, but it's a safe bet your engine is also not reliant on radiation.....hence, it makes little difference, even if the paint used on the engines at the factory had very high emissivity and was black in the infrared spectrum (it would not necessarily appear black to the human eye, though), it still would not shed heat fast enough to cool your Suzuki (or your Porsche :)) even at a low 2000 rpm, absent any airflow.
I prefer the silver engines myself, strictly for cosmetic reasons.....hard to beat the look of a super-clean silver one, but that's JMO...... to each his own. ;)

Tony.
 
emjay said:
Faster, too! ;) :rolleyes:
Click to expand...

I agree! :D

DSC00815-1.jpg


Eric
 
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