Exhaust heat management
||This article contains instructions, advice, or how-to content. (November 2013)|
The fact that exhausts often pass near important components means that ways of protecting these components from heat soak are especially important. As a result heat management is used as a way of reflecting, dissipating or simply absorbing the heat.
Heat shield is also useful to reduce under-bonnet temperatures which therefore reduces intake temperature, subsequently increasing power.
There are many different types of heat management, some more effective than others. They range from basic solid heat shield to plasma sprayed ceramics.
Heat shield is one of the most widely used heat management options available due to its relative low price and ease to fit. In the past it has usually been custom made from rigid steel; however, flexible aluminium is now the standard.
More recently technology has become available to apply ceramic thermal barrier coatings onto flexible aluminium in order to increase the thermal insulatory properties. This same procedure is also used on composite materials, which is often used on high-performance race cars, such as in Formula 1.
This fairly low-cost solution can offer minor reductions in heat loss. It is often applied by brushing or spraying from an aerosol onto the exhaust system, followed by curing in the oven to allow the paint to adhere. This is sometimes applied to the internal surfaces of the exhaust however this often flakes prematurely due to the inability to clean the surface prior to application. It is usually necessary to reapply every 1–2 years due to it flaking and peeling.
Thermal barrier coating
These ceramic coatings are highly advanced coatings applied via plasma spray, and as a result, the coating is effectively welded to the surface of the exhaust system. They can offer significant performance benefits due to the low thermal conductivity of the ceramic compound. These coatings protect steel exhaust systems further by protecting from rust.
This is the cheapest solution and is quite easy to apply. Heat wrap consists of a high-temperature synthetic fabric which is wrapped round the manifold. Though often sold as a cheap and easy way to boost horsepower, exhaust wrap does not increase engine output much. It can, depending on the vehicle, decrease engine bay temperatures, which can, depending on how the engine intake is designed, lower the intake air temperature, and therefore increase the air density, which may result in an increase in efficiency and power.
Heat wrap or thermal barrier coating?
There has been much debate if heat wrap is better than plasma-sprayed coatings. The far cheaper option in the short term is heat wrap but whilst being quick and easy to apply, it lacks a great deal of aesthetic appeal and is normally less effective. The fact that heat wrap degrades the manifold, means that within a couple of years, a replacement manifold is required therefore it is important to factor in this extra cost before deciding to choose heat wrap. Ceramic plasma-sprayed coatings also have far greater performance benefits and whilst being quite expensive, they last a long time and in fact protect the exhaust manifold.
- Hosier, Ralph (2013), BMW E30 3 Series: How to Modify for High-Performance and Competition, Veloce Publishing, p. 61, ISBN 1845844386