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I'm gonna make a manifold for my gtst, was wondering if any one had any opinions on what material to use, also what diameter the pipe work needs to be,

I know 304 stainless is the the most common but that usually because it's cheap
 

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Mild steel seems to be best for beak soak etc, as long as it's coated once complete should last a long time too. I believe the 6boost manifolds are made from mild steel too. The diameter will only be restrictive on engine bay room and turbo placement, as long as it's bigger than the outlet from the head :)
 

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Definitely us steam pipe, mild steal is okay, but steam pipe allows a little flex so that it doesn't break

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UNS-32100 has nearly the same properties as 304H s/s, due to its higher carbon content, 304H can handle elevated working temperatures above 525°c. 304H is probably easier to source too. 304L would probably work just as well unless your going to use it as a track tool.
 

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UNS-32100 has nearly the same properties as 304H s/s, due to its higher carbon content, 304H can handle elevated working temperatures above 525°c. 304H is probably easier to source too. 304L would probably work just as well unless your going to use it as a track tool.
I was always under the impression UNS-32100 handled higher heat better..

Type 321 is a stabilized stainless steel which offers as its main advantage an excellent resistance to intergranular corrosion following exposure to temperatures in the chromium carbide precipitation range from 800 to 1500° F (427 to 816° C). Type 321 is stabilized against chromium carbide formation by the addition of titanium.
While Type 321 continues to be employed for prolonged service in th4e 800 to 1500° F (427 to 816° C) temperature range, Type 304L has supplanted this stabilized grade for applications involving only welding or short time heating.

Type 321 stainless steel s also advantageous for high temperature service because of its good mechanical properties. Type 321 stainless steel offers higher creep and stress rupture properties than Type 304 and, particularly, Type 304L which might also be considered for exposures where sensitization and intergranular corrosion are concerns. This results in higher elevated temperature allowable stresses for this stabilized alloy for ASME Boiler and pressure Vessel Code applications. The Type 321 alloy has a maximum use temperature of 1500°F (816° C) for code applications like Type 304, whereas Type 304L is limited to 800° F (426° C).
 

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304H will handel heat from 525° upto c 800 °c. UNS321 will handel upto 900°c, If you really want to go the whole hog, you could use 310 wich can take 1100 °c or S30815 at 1150 °c . I doubt operating temperatures are above 800 °c so I reckon 304H will do, it will be cheaper and probably a lot easier to source. Weldability is similar to UNS32100.
304 & 304L are not in the same classification as 304H due to reduced carbon content.
 

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i would go with the mild unless this is for some form of large expense project,,, stainless looks brilliant,,,, just remember, stainless expands and contracts like you would not believe, (would think a 6" length could easily grow by an extra 1/4" if not restrained,, and warp) so just to put this in to plain english, all those lovelly manifold branches welded in between two flanges all of diferent lengths will contract and expand at diferent rates and with diferent force (sure me n bruce have a thrtead somewhere on here about it,) anyway, thats why all the ebay stainless manifolds that are cheap end up eating turbo gaskets, giving boost leaks, running badly, and pissing the users off. the flanges all end up warped to hell,,,,, generally speaking stainless is a pretty bloody bad choice for anything getting hot and cold that cant be allowed to expand and contract,,,, plus generally theyre not internal purged during the welding proccess creating bad air flow of the exhaust gasses, if youve ever looked inside a stainless manifold and noticed little rough bits of black on the inside of the pipe where welds are,,,, thats because its not being purged properly (if at all)
not trying to put a spoiler on things, but the whole stainless debate annoys me because hardly any of it is done what i would call correctly. :) hope that helps..
 
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