Should i have coated my intake manifold?

[Alastor187]

Originally Posted by curtis73

Keep in mind that temperature and heat are two different things. Just because the surface of the manifold has a lower temperature than before does not mean that the amount of heat is any different.

your example of the steel and wood are a perfect analogy. They are both the same temperature, but the steel has more heat in it and a higher heat capacity, making it feel colder. Another analogy is reaching your hand into a hot oven which doesn't burn, compared to touching the rack in the oven which does.

The coating on the intake is preventing heat from transferring out of the manifold and into your hand, but that should not necessarily be an indicator of how much heat (or temperature) is contained the aluminum "meat" of the intake.

That is what I was trying to get at with the link to thermal effusivity, but there was a typo in the address that is now fixed.

Per the link:

It is important to realize that while the two expressions contain the same parameters, they are quite different. Diffusivity is related to the speed at which thermal equilibrium can be reached. Effusivity (sometimes called the heat penetration coefficient) is the rate at which a material can absorb heat. It is the property that determines the contact temperature of two bodies that touch each other.
For example, it explains the well-known but often misinterpreted effect that a metal feels cold to the touch and wool warm, even when both are at room temperature. Our finger is a very poor temperature sensor (that is, of the temperature of the body it touches, not of the contact temperature), but a sensitive heat flux sensor. The contact temperature is lowest for materials with a high thermal conductivity and a high thermal capacity, explaining why metal feels cold.

Originally Posted by Bima_Bima

yeah i know you can't feel temperature (thats why a 10*C bit of steel feels colder than a 10*C block of wood) but i am able to hold the manifold continuously where as previously i was unable to do it for more than a second so its defintely hotter (remains to be seen how different it is when cruising with hood closed). As for radiation i don't think its an issue since radition is T^4 function so its more to do with the thin layer of paint being a increase in thermal resistance IMO. The only real way is to place a probe in the end of the runner and also the start of the manifold to see the temp increase due to manifold under different conditions (cruising , WOT) but i am not concerned enough to start putting holes in the manifold maybe if need to i remove it again it might be an interesting exercise.....

I agree that for this case radiation is probably not that significant, but not for the same reasons.

Assuming the outside of the intake is really cooler; then it is probably safe to say that more heat is being transferred into the intake air stream. The only question is does it really matter (that is, is it too hot now)? So unless you are going to measure the air temperature or try to calculate how much power is being transferred to the air, there really is no easy way to figure it out.

[MetalHeadZaid]

i know this is a little off topic but a friend of mine painted his intercooler black with just regular repco (like autozone or napa) spray cans. if paint has an effect on how a unit retains or expends heat, does this mean he's done something bad?

EDIT: this is a front mounted (OEM lancer evo 3) so i wouldnt think it's affected by engine bay temps.

[speedworld]

why no image?