Post by
king_johnthegreat »
https://forums.nicoclub.com/king-johnthegreat-u2837.html
Fri Nov 15, 2002 10:22 am
The importnat part of the statement that basically contradicts the idea that heat is the factor for failure is "heats up AND COOLS." They don't crack until they have cooled, and too quickly for that matter; making the dissapatory property the one at fault, not the opperating teperature. IF the manifold doesn't cool TOO QUICKLY, it is highly UNlikely it will crack. That is why certain applications demand a certain amout of material in density and thickness. If a wall is too thin it will cool too quickly, inside and out. A thicker wall retains higher core temperatures longer, causing the manifold to take longer cooling down. Stainless is the best of the three materials we have discussed for self insulation, and is inherently better for making a manifold that doesn't require such a thick wall, or for mani's that must suffer from higher heat, such as in a turbo app. Again, the greatest cause for breakage is stress fractures resulting from poor design, improper or insufficient amount of material for controlled dissapation and cooling, and inherent metal stresses. I have seen metal that was so hot, it was actually burning. I mean, it was emanating flames sustained by the gases released by the metal itself; no other source for ignition but self combustion. When it cooled, it did not crack. Explain how that might of happened, considering it was a lesser grade iron than typically used for manifolds. And, for the sake of being technical, EXACTLY where does the exhaust gas attain the speed of sound (i.e.: the combustion chamber, the exhaust port, the primary, the collector, the down pipe, etc.,)? John