is it true ??
- Thread starter PGH PA 2 STROKE
- Start date
i have heard that that is true to an extent. i believe that it holds the heat in. but i have also heard that if you paint it white it repels heat or whatever. i think on horsepower tv or one of those shows, i saw them paint the bottom of an intake manifold on a v8 white, and they dyno tested it and if i remember right, it picked up a horsepower or two once the engine was hot because the white didnt hold the heat of the oil in the valley, so maybe it just depends on the color?
A coat of black will actually keep it cooler, but going crazy with painting will hold heat in and make it run hotter.
Some overhaul shops claim beneficial cooling effects of black paint on their engine. The theory is that black is a better emitter of infrared (heat) energy. A hot engine in a cold surrounding, radiates energy from the hot object to the cold. The amount of radiant cooling (thermal emissions) is generally dependent upon the temperature of the emitter (engine) and how efficient the engine is at radiating energy — its emissivity. This derives from Kirchoff's Law where good absorbers are also good emitters. Since black is a good absorber of energy (that's why it's black), it's also a good emitter. A black object emits more radiant energy (cools faster) than a white or gold object that emits less radiant energy per unit of time. Painting an engine black increases the amount of radiant energy emitted by the hot engine to its colder surroundings and it will be cooler than a non-black engine.
Most heat energy emitted by the engine is in the invisible infrared portion of the spectrum. What appears to us as black, white, red, or green in the visible spectrum is not what we would see in the infrared spectrum. Any color of paint that uses organic (non-metallic) pigments is black in the infrared spectrum. For example, white paint emits 90-95% depending upon pigment type. Black emits 96%, blue 94%, green 92% and red 91%. The best emissivity surface coating is acetylene soot at 97%. Painting an engine increases radiant cooling but the color of the paint doesn't.
Improving Engine Cooling by Painting
Most heat energy emitted by the engine is in the invisible infrared portion of the spectrum. What appears to us as black, white, red, or green in the visible spectrum is not what we would see in the infrared spectrum. Any color of paint that uses organic (non-metallic) pigments is black in the infrared spectrum. For example, white paint emits 90-95% depending upon pigment type. Black emits 96%, blue 94%, green 92% and red 91%. The best emissivity surface coating is acetylene soot at 97%. Painting an engine increases radiant cooling but the color of the paint doesn't.
Improving Engine Cooling by Painting
Black transfers heat faster than any other color. It heats up the fastest, but it also cools the fastest. Since you're engine will be hotter than the surrounding air, it will cool the faster than say white for an example.
The white on the bottom of that intake manifold was prob to reflect engine heat from the intake thereby keeping the intake charge cooler.
