304SS vs 316SS

[tristanlee85]

I am getting rid of my current turbo manifold and plan on building a new one within the next month. What I currently have is made from 304SS and mild steel flanges. Looking at McMaster, there is about a $2 difference between 304SS and 316SS butt-weld fittings. I'm not exactly sure which type to go with. My gut tells me 316, but I don't know enough about the properties of the steel to know exactly which type to go with. Many tubular turbo headers that I see are made from 304SS as it's pretty cost-effective. However, with 316 on being $2 more, if it's better for my application, then I'm going to spend the money on it.

 

Professional opinions please.

[AJ]

you want 321SS for a turbo so it doesn't crack. i've never seen anyone use 316SS

[tristanlee85]

Hmm. I'm just getting mixed opinions about this (not that I don't trust your advice) and I haven't been able to find an exact reason why I should choose 1 metal over the other. Speaking with a welder who has been making turbo manifold as a professional career, and a side-project of www.alphatuning.com, he says:

 

304 is fine. only reason i use 316 some times is when 304 is out of stock. i've never used 321. 321 has better heat capabilities, however the heat isn't what kills exhaust manifolds. its the pressure, heat, vibration, heat cycling, gas and weld quality that break down a manifold.

 

get the 304 and call it a day.

 

I can't remember if we discussed this before because I don't have our previous e-mails' date=' but is there any reason to not use 316SS over 304SS. I'm looking to do a build here and notice that McMaster only offers 304 and 316. I did not see 321 listed on their site. [/quote']

 

Yet, it seems like the consensus when a manifold cracks is "well, you shouldn't have used 304". I believe Full Race uses either 304 or 308. Also, the carbon rating of 321 is much higher than 304. Wouldn't that increase the harness and be more prone to cracking?

 

I also found this. It seems like 304 and 321 have similar properties, but don't think I am saying the quality of 304 is that of 321.:

http://img149.imageshack.us/img149/4268/steely.jpg

 

I'm not sure how relevant that information is to the topic at hand, though.

[criitter7]

304 is all you need with those butt weld things

[AJ]

reread what that guy sent you

however the heat isn't what kills exhaust manifolds. its the pressure, heat, vibration, heat cycling, gas and weld quality that break down a manifold.

 

 

From what research I've done on the subject, you only need to step up from 304 after you reach around 15psi of boost, or somewhere around 1600º F EGT's.

http://www.pro-touring.com/forum/showpost.php?p=13180&postcount=5 also read post #10

[TurboTank]

i would spend more time thinking about the design to allow the expansion to happen with out cracking the runners, other than what material to use. ur proably looking to use sch10 or sch 40 weld bends. both of those are pleanty thick enuf for a turbo manifold. the amount of boost isnt relitive to anything..to many variables. mr burns himself said its not if an manifold will crack, its when.

 

another thing to consider is how those thicker weld bends are welded. alot of people dont understand how to weld them. they need to have 2 passes done, a root and a cover pass. you can pm if you have any other questions.

[tristanlee85]

I won't be the one welding. My job is to cut and tack weld everything, and then my friend who I mentioned in this post will be doing the welding. And all of the pipe is schedule 40.