A new ingredient to porting recipes?

[Nutball]

I learned something new today, but haven't yet tested to see if it is true... because it's weird enough to still make me doubt.

Apparently color not only affects heat absorption, but also emission. So, I would normally prefer to polish the head, piston, and exhaust port to trap heat in for 1) higher pressure, since pressure comes from heat, and 2) to keep the piston and cylinder cooler from absorbing heat... until both get covered in carbon again.

Apparently, it would also be good to paint the cylinder black as if black is a heat transfer medium that will make the heat in the aluminum more quickly emitted.

In a simple thought, it seems obvious: black absorbs well, why not emit well too? I used to only think about material and surface area for direct heat transfer, and assumed a polished surface would transfer heat better to flowing air because of the boundary layer being thinner. But then I think a polished exhaust port will reflect better because I'm thinking in terms of IR radiation, not conduction with the exhaust, though I mainly polish the exhaust, if I do, for better flow.

Now here's a question. Which would cool better: a polished glossy black anodized cylinder, or a sand blasted matte black painted one? The latter will absorb light from more directions even though it is just as black. Does that mean it will emit better? What if it was polished smooth, but still a matte black (as polished as can still be called matte)? Then you have to think about how a matte surface will have more emission surface area, but a thicker boundary layer.

Anyway, in general should we start coloring cylinders black? Maybe on hot climate saws or milling saws?


I tried wood stove paint, and baked to 500F, looks good, but not as black as it could be. A Farmertec cylinder would be half way there. Maybe if I just cover it in soot from a candle flame...

 

[Dub11]

I read once in a hotrod mag that they use to paint blocks black and the bottom of the intake manifold white.

Not sure if that helps any.

 

[srcarr52]

Food for thought.

Polished surfaces have a larger boundary layer because of less disturbance (aka tripping). I.E. look at rough vs. smooth pipe studies.

Paint does add in some insulation value, is this overcome by the increased radiation as opposed to the lost convection through the paint.

How much of the extra radiated heat escapes and doesn’t get refracted by the covers.

 

[Canadian farm boy]

How many aluminum radiators do you see painted black?
How many copper radiators do you see painted black?

Aluminum is extremely good at dissipating heat.
Imo painting an aluminum saw cylinder black won’t make much difference at all in terms of dissipating heat and actually might make it worse

 

[jacob j.]

There was a local builder here years ago that drilled random holes in the cooling fins.

So maybe if a guy drilled random holes and painted his cylinder black, he might really have something?

 

[Stump Shot]

Was told to me that a "special" paint was used on cylinders to make them dissipate heat faster by manufactures. What this paint actually is, I do not know.

 

[Dub11]

Was told to me that a "special" paint was used on cylinders to make them dissipate heat faster by manufactures. What this paint actually is, I do not know.

It probably maxed it out paint.

 

[Nutball]

I'd assume a metallic paint would work best for conduction heat transfer too.

 

[Nutball]

Food for thought.

Polished surfaces have a larger boundary layer because of less disturbance (aka tripping). I.E. look at rough vs. smooth pipe studies.

Paint does add in some insulation value, is this overcome by the increased radiation as opposed to the lost convection through the paint.

How much of the extra radiated heat escapes and doesn’t get refracted by the covers.

I guess the same air slips by a polished surface then that air will get extra hot and not as effective at cooling, while a rough surface would exchange the air better.

 

[RI Chevy]

How about coating these 2 stroke pistons? They coat pistons in high output motors, why not try one with a 2 stroke? They are supposed to dissipate heat better...

 

[srcarr52]

How about coating these 2 stroke pistons? They coat pistons in high output motors, why not try one with a 2 stroke? They are supposed to dissipate heat better...

They ceramic coat domes to absorb less heat.

 

[Mastermind]

I used to spend time polishing.....

Not anymore. After tearing down a saw with a polished exhaust a few months down the road, I realized that it's a complete waste of time on a real life working saw.

I ain't painting no jugs either. LOL

 

[RI Chevy]

They ceramic coat domes to absorb less heat.

Yes sir. To dissipate heat and run cooler. Have you ever tried one in a 2 stroke application?

 

[srcarr52]

I used to spend time polishing.....

Not anymore. After tearing down a saw with a polished exhaust a few months down the road, I realized that it's a complete waste of time on a real life working saw.

I ain't painting no jugs either. LOL

Zactly!

 

[usmcbuckwild]

How many aluminum radiators do you see painted black?
How many copper radiators do you see painted black?

Aluminum is extremely good at dissipating heat.
Imo painting an aluminum saw cylinder black won’t make much difference at all in terms of dissipating heat and actually might make it worse

This is the exact reference I was going to make. Older radiators were painted to assist in preventing corrosion. Post 1970s all radiators were left raw/natural due to better alloys. They shed and/or transfer heat better in raw form.

Engine blocks were painted for aesthetics. Race engines run raw casting or are polished under intakes as they distribute the shed heat better. Yes, some coatings are proven to reflect/reduce absorption of heat. Most piston coatings (to my understanding) are done to reduce friction. Carbon build up on pistons causes changes in balance (as well as hot spots as the carbon burns) hence why they are coated. Not to reflect/deflect heat; but to not allow carbon to build up on them.

 

[Nutball]

It wasn't a perfect test, but I tried testing 4 of the same pieces of aluminum: one polished, one shiny but very rough, one a scuffed anodized black, and one polished anodized black. The black ones turned a very dark red after heating, but they all seemed to cool down at the same speed. They were set on wood stove window glass with cardboard dividers between them. Obviously the shiny ones look less hot than the anodized ones with an IR camera.

 

[Al Smith]

Who was that guy who looked like Doogie Howser ,"Simon " maybe ? Really just a figment of several peoples vivid imagination .Claimed black paint did something .I never took the bait . Back in the 2 cycle kart era they removed the paint .To paint or not to paint,that is the question .