Originally posted by DemonSVT:
A large reason why it is beneficial is the decreased under hood temperatures and not the fact it helps retain heat energy in the exhaust gasses. This is the same reason the stock precats and Y-pipe are clamshell shielded. There is less heat transfer to the engine bay & oil pan.

That site was mainly for using coatings over wrap. There is no argument there because a quality coating is superior to a wrap in longevity of itself and the piece in question.

Now the durability of aluminized steel far surpasses what most people give it credit for. Metallurgy has come a long way. My headers are 4 years old. From the collectors back have been wrapped for over 3 of those years. My Y-pipe/down pipes have also been wrapped for 3+ years. First as a Y-pipe and then as part of my duals a year later. None show any significant degradation. Yes the headers have a basic ceramic coating. Yes I sprayed everything with Thermo-Tec when I did my 3L. (over 2 years ago now) I did not wrap the primaries for concerns of over stressing the metal.

The important part is that you can touch the wrap even after spirited driving. Regardless of the extra stress on the metal the fact that exhaust heat is not entering the oil pan and engine bay are worth it to me. I will let everyone know when I have to build another set of down pipes.



Airgap manifolds,be they clamshell or hydroformed, are done for two reasons...the main one is to retain the temp of the exhaust feed gas to the cats,this reduces heat loss and 'light off time' of the cat. A spin off is better /lower outer manifold skin temps. On airgap hydroformed down pipes noise reduction is another spin off. The 'inner' liner is usually around 2/3rd the thickness of the outer and of a higher rated s/steel.On some applications re the 'Benchmarc'(TM) cat developed by Benteler(heat retaning cat) the airgap is a sealed vac unit for insulation and heat retention in the cat for rapid light off,we also used 'Aerogel' in the vac space(liquid smoke) as an insulator.Look up the 'Benchmarc' cat ,very interesting project I worked on while at Benteler with
Dr Biel.

....if you understand what the pre-cats/'light off' cats do Re INCREASE the feed gas temps from the manifold to feed the main underbody cat for 1)Reduced cold start light off times 2)Reduce the chance of the main cat 'dropping out' Re reduced feed gas temps which cause the main cat to stop working at low speeds. This tells you that one of the hottest areas in the exhaust 'feed gas' temps is in the 'Y'
pipe.Changing the Y pipe from stoc to an off road 'MILD STEEL' type with stoc exhaust manifold with the cats still in place,is asking for trouble with the mild steel exposed to elevated gas temps which will cause it to oxidise at a rapid rate. The materials chosen for the V6 manifolds and Y pipe were very well chosen to retain feed gas temps to the cats and give longevity in service re rate of oxidising etc....The S/Steels used in this system are very expensive Vs 'mild steel'...

...for headers etc, is another area where 'eggspurts' mess up. There are TWO type of heat coatings. One type
INSULATES the component to RETAIN heat, the second helps CONDUCT heat OUT of the component(do YOU know which type you have on your headers???LOL). The insulation type would be fine on say a stainless steel pipe in a turbo system where the heat of the exhaust needs to be retained within the pipe for added power, but NOT with a mild steel pipe as this will increase the rate of oxidisation of the material. Conducting more heat OUT of the pipe poses the question of added heat to the surrounding components. The 'best' would be tube hydroformed s/steel headers with an air gap and thin liner tube. These have been made as we designed many proto sets at Benteler BUT the cost to hydroform such designs is VERY costly and anyone who knows materials
and hydroform technology will confirm this. Hydroform
tooling, presses, dies etc are VERY expensive and 'blowing tubes' to give a uniform air gap between the inner and outer tube is a design 'art', of which very few engineers or mfg's fully understand. Benteler has always been at the front in hydroforming, to the point where they design and build their own hydroform presses(in Germany!),which range from 500 to 1000 tons. Been there done that!!!!!!





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