Contour Enthusiasts Group Archives Forums Modifications Duratec Performance aluminum or plastic heatsheild?

Originally posted by Rishodi:

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Originally posted by warmonger:

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Originally posted by Rishodi:

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Aluminum is a conductor. Plastic is an insulator. An aluminum heatshield on its own will do little to actually insulate your air intake because it heats up rather quickly. If you insulate the aluminum with something though, then that's ideal because it will both look better and perform as well as a plastic heatshield.

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This is incorrect.
All it has to do is stop the flow of hot air into the filter from the engine compartment and force the intake to draw from the fender or other cooler source. Any material that does this will work.
Plastics conduct heat a little slower but they still conduct a significant amount of heat and they will get just as hot as the aluminum.

The static layer of air is the real insulator, no the plastic and not the aluminun....same principal as a sleeping bag.

Both plastic and aluminum will stop radiant heat. Think of radiant heat as "light waves". Any mirrored surface will reflect some and any flat surface will absorb. This still doesn't matter as the static layer of air on the inside of the box near the wall is your best insulator. Radiant heat isn't an issue with the airflow so much as the non-moving parts. The biggest culprit is conduction to the air from the readiator and manifolds/pipes that flows throughout the engine bay. After it is in contact with these components and absorbs heat through conduction, convection, and advection, it gets sucked into the engine. THAT is the killer.

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True enough, except for the part about plastics conducting heat "a little slower". Plastics have a much higher specific heat capacity than aluminum and will thus require a much higher influx of heat to reach the same temperature as aluminum. Also, the air inside the heatshield is not quite static like a sleeping bag; after all, it's contiually being sucked into the intake. Thus, this is all a moot point if there is no inlet for cold air, such as the stock air inlet hose.

Anyway, if I was going to make my own heatshield, I would construct it out of aluminum and then coat the inside with some sort of foam insulation. The air bubbles inside foam insulation create lots of static air space and indeed that is one of the best ways to insulate from heatsoak.

Okay, enough on this subject anyway. Screw the heatshield and just get a CAI, it's better on all counts

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That is also not correct If I RECALL (IIRC)

IIRC most solids have a heat capacity on the order of
6 calories/mole*degreeK

Substances like styrofoam have a cellular structure that impedes the flow of heat due to reduced cross sectional area of the cell walls, but the material corrected for density is very similar in heat capacity. Also, temperature rise is the same for these materials when the source temp is constant. The airflow is dynamic so the rate that it will pick up heat will be slower with certain materials than others since the heat conduction is lower in some materials than others (i.e. metals versus styrofoam).
In a very short time everything in that engine bay and on that surface of that motor will be at comparably similar temps irregardless of composition.
If you don't believe me, take a thermocouple and measure the temperature of the intake manifold surface (aluminum), then measure the temperature of the spark plug boot (silicone) when the engine is at a steady state operating temperature.