Painting your engine

I know for cooling the best is ether bare aluminum or flat black, I see some guys painting the cam cover red to accent the bike, I've seen some paint the whole engine black, which would seem ok for cooling, but what if you painted the cylinder and valve cover red, wiping the fins to bare metal and leaving the crack case aluminum or flat black. Do you think there would be cooling problems?

 

Color of paint shouldn't effect temperature.

 

Agreed, the color of the paint should make no signifigant change in operating tempurature, but adding a coat of paint to the whole engine could decrease its cooling effiecincy mainly becuase the cold air passing over the fins would also have to cool the paint IE. More mass to cool, although i dont think it could be to severe.

 

I think Id worry more about the insulating quality of the paint used...

 

As far as my understanding goes there are two main methods of heat transfer for the engine cooling - Convection (heat loss to the air) and radiation - (Heat loss through the emmitance of infared light/heat)

The formula for radiation heat transfer basically depends on multiplying the 'Surface emissivity factor' by a function of the tempurature.

I believe the emissivity of bare aluminum is around .1-.3 whereas flat black is 1 (glossy black is back to around .1 I believe).

So basically if you have two engines at the same tempurature the flat black one will emit around three to 10 times as much heat through Radiation.

However at high speeds the heat loss to the air through convection is going to be so much higher that the radiation heat loss will be insignificant in compairison. However when motionless I think that about as much heat is lost by radiation as convection for things in the tempurature range of engines and so the flat black can actually help things considerable (1.5-5 times the heat dissipation).

However I believe that if the coating is thick like most home paint jobs the paint will insulate the engine and reduce any advantage that the flat black paint would help.

But if you look at high performance bike engines you will see that the vast majority have flat black paint that is in fact very thin and therefore would have almost no insulating properties. Anyway since your not proposing to paint the entire engine I would bet that you wouldn't see any significant tempurature gains (maybe like an extra 5 degrees on a really hot day where your just idling in traffic all day).

I think that as long as the engine is clean your going to be fine.

 

Cool, pun intended, I also found this article
http://www.sacskyranch.com/paint.htm

 

Wow interesting reading - thanks fore4runner