Thermal wrapping will help because it'll help slow down the temperature gradient from operating temperature to idle. However, if it's going to crack, sooner or later, it'll crack. The best way to prevent this is by getting a manifold made out of a stainless alloy that's designed for temperature cycling.
Originally posted by xtal Thermal wrapping will help because it'll help slow down the temperature gradient from operating temperature to idle. However, if it's going to crack, sooner or later, it'll crack. The best way to prevent this is by getting a manifold made out of a stainless alloy that's designed for temperature cycling.
Steve
Wrapping the manifold would be the worst thing to do. The thermal wrap keeps all the heat in the manifold.
*sigh* Yes, you get higher temperatures with a wrap. It is not the higher temperatures that cause the cracks. It is the derviative, or rate of change, in the temperature that causes the problem. When you turn the engine off on an unwrapped header it will VERY RAPIDLY cool down. This is a large part of the problem.
Further, this is more of a problem when you have a part that has manufacturing defects, or is a cast part, or the material is sensitive to large changes in temperatures like some stainless steel alloys. There are many different alloys of stainless steel which have very different responses to temperature cycling (and have costs to match).
There are other reasons to do it too, and other reasons not to. This is just my opinion, and should be taken for what it's worth ($0).
Best material to make a manifold out of is Grade 8 Forged Stainless. Unfortunately not many companies can afford to offer them. So they cheap out and use Lower grades of steel. This causes cracks due to extreme Thermal expansion. Lower grades of steel aren't meant to take this abuse. Wraping the Manifold helps quite a bit, because it holds the heat in, which causes the manifold to cool more slowly. This helps to prevent cracks. Also supporting the manifold and turbo with braces helps A LOT. You can buy Grade 8 Forged stainless from www.burnsstainless.com try designing a manifold yourself, and find a good welder to put it together for you.
"We get lots of questions about the thermal wrap products that are seen on various classes of competition cars. it's natural to assume that because racers use a product, it must have some performance benefit. The theory behind thermal wrap is that maintaining the combustion heat in the exhaust system improves scavenging. But on street driven cars any small advantage you might gain is offset by ugly side effects.
Racers don't mind replacing exhaust system components frequently -- you will. On street driven cars, you want to get rid of the heat. The higher the exhaust system temperature, the faster you'll burn out gaskets and destroy the headers, converters and mufflers. Unless you've got money to burn, our advice about using thermal wrap is DON'T!"
Nobody asked about other effects, just cracking. . Also, FWIW, most of the aftermarket parts are made out of the lowest-spec metal that they can find, and that's the reason they crack. It's also one of the reasons expensive parts cost so much more - materials are of higher quality.
I don't buy the arguement that higher temps will be that much worse on the gaskets and such, or worse on the exhaust in general. I could even see arguements how it would help. However, without hard data - you know, those measurement things - nobody would know for sure.
wouldnt a turbo timer help? b/c it keeps the car on for a little bit while the turbo cools down slower and the manifold too. just a theory
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. Also, FWIW, most of the aftermarket parts are made out of the lowest-spec metal that they can find, and that's the reason they crack. It's also one of the reasons expensive parts cost so much more - materials are of higher quality.
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