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PTPTurboBlankets
08-23-2013, 03:49 PM
Hello Fiat 500 USA Forum,

To the moderators: I hope we have not violated any rules by posting as a representative of our company without vendor status. Our only intent with this post is to clear up any confusion, and to protect our brand from unfair statements we received by a competitor.

Inconel was one of several materials considered in the design of PTP Turbo Blankets. PTP decided against using inconel because it didn't make sense for the objectives they were trying to achieve.

To explain this, it probably makes sense to walk through a little about heat transfer. As you may know, there are several forms of heat transfer. The types at issue here are conduction, convection, and radiation. (there is also advection, but that is irrelevant for this discussion) As you may know, "conduction" is the transfer of heat (or other energy) between objects that are in physical contact. (e.g., when you touch a hot skillet, you're feeling the heat that has been transferred from the burner to your hand via conduction through the metal). As you may also know, "convection" is the transfer of heat between an object and its environment, due to fluid motion. (e.g., when your car heater blows hot air, the interior of your car is being heated by the convection of air(forced convection)) As you may also know, radiation (radiant) heat transfer involves the transfer of heat from an object by the emission of electromagnetic radiation. (e.g., the sun heats the earth by radiant heat transfer) The prevention of different types of heat transfer requires different methods.

Inconel serves well as a radiant barrier. In other words, it does a good job of reflecting away radiant heat from a heat source. (such as reflecting the heat of the sun away from the interior of a building with reflective window treatment) The problem is that a radiant barrier must have an air gap between it and the heat source to perform effectively. Because a radiant barrier, such as inconel, is a metal (an alloy specifically), it conducts heat very well. That would be fine if there were no contact with the heat source (the turbocharger), but if the inconel is in direct contact with the turbocharger, the conduction of heat from the turbocharger would completely overwhelm any gains made by preventing the radiant heat transfer.

By contrast, if the inconel is not in direct contact with the turbocharger (such as if there's an air gap between the two via the factory heat shield), then the inconel would reflect radiant heat effectively. The problem is that if there's an air gap between the turbocharger and the turbo blanket, convection will be a huge source of heat loss. (the hot air between the turbocharger and the heat shield/turbo blanket will continually escape, cooling the hot side of the turbocharger and heating the engine bay)

Remember, our objective is to minimize heat loss from the hot side of the turbocharger. This enables the turbocharger to spool up quicker (hotter exhaust gases travel faster at a given RPM because they're more expansive). This also keeps the cool side of the turbocharger cool so that the intake air is as cool as possible (ensuring that the intake air is rich with oxygen per unit volume). This further prevents heat-related damage in the engine bay.

A radiant barrier such as inconel would reflect heat back, but a substantial amount of heat would escape if there is an air gap between the turbocharger and the heat shield or between the turbocharger and the inconel surface. You can understand this problem by imagining yourself lying in bed under a thick blanket. If the blanket is held some distance above your body by a small tent frame, for example, you would not stay nearly as warm as if the blankets were laid directly on your body. The convective heat loss resulting from air gaps can make a huge difference. (the problem is lessened if the air gaps are completely sealed off from the exterior air, but that is not the case here)

PTP carefully considered using inconel and decided that it was not a good idea. This was for the reasons explained above and the problems it posed for heat insulation. In addition, PTP’s studies have found that Inconel is more susptable to puncturing. Also, because there is no weave (such as with PTP's silica) the puncture can easily spread to form a rip. PTP also found that inconel does not conform to shapes as easily as a woven fabric - further exacerbating the air gap problem.

To summarize, air gaps are the enemy of proper heat insulation. This is why PTP recommends installing our turbo blankets directly onto the turbocharger. (not over the factory heat shield) The turbo blanket should be installed snugly and with a minimum of air gaps.

I hope this explains PTP’s position on inconel. If you have any questions, feel free to ask!

Thanks,
PTP Turbo Blankets