Just like the title says. Also is 321 stainless better than aluminized steel? What are the pros and cons to those two? I know 304 is the best, but after that.
I ask because i have long tubes for my Camaro and i just found out that they are 321 stainless. Do i have to worry about warping or cracking from exhaust temps? I got them pretty cheap but i could have gotten pacesetters for the same price. The thing about pacesetters is they are proven to work they just rust.
I hope these work out, i just don’t want to be too disappointed. Any help is greatly appreciated. Thanks.
321 can handle higher temps and is less suspectible to corrosion. 304 is the most common of all the 300 series of stainless. 321 is also about 2 x the price of 304. 308l can weld 321 stainless together if temps do not exceed 840 f, otherwise, 347 should used for the joining of 321 stainless.
321 is basically austentic 18/8 steel (aka 304 stainless) which also contains titanium which allows it deal with the heat as they said. Its good up to generally 900 C. Very resistant to scaling and less prone to crack under stress.
For instance.
You could make an equal length manifold out of .065" (16 gauge) 321 stainless steel and when properly braced it will stand the test of heat and time.
Where as if you were to use 16 gauge 304 stainless steel in the same application it will fail. It cannot stand the same heat and vibration as 321 thin wall and will surely crack in short order (within 3 months depending on quality of the product and weld)
So how thick would one have to go to have comparable results with 304, I understand that 304 may never be able to take the heat that 321 would. For say like a turbo application with an exhaust manifold out of 304, would 304 be acceptable here. and what thick ness of tubing would be appropriate?
In forced induction most tubular manifolds are constructed from 1 1/2" Sch 10 304ss pipe. Pipe is measured differently from tubing. Tubing is measured on the outer diameter. Pipe is measured on its nominal size that does not mean that it will have an inner diameter of the same dimension it just means it wont have an outer diameter of less than the rated.
Personally, I am not sure how they rate scheduling, Im sure some more delving into the matter would uncover an answer. I imagine there is a formula or ratio of diameter to determine the thickness for any given schedule as the amounts change with nominal pipe size.
For our purpose though we will focus on what is most widely used. Which is 1.5" 304ss sch 10 pipe. Why this is used is probably a cost issue and something that was found to work over time from trial and error as Forced induction hasn’t really been in the main stream for more than about 30 years and even more so within the last 10 which has seen 10fold the amount of development in technology.
Any how.
1.5" sch 10 304ss has a wall thickness of .109". This is almost double that of standard use tubing of the same grade which is generally .065". Heat soak combined with inherent vibration from a reciprocating mass and a heavy object (turbo, and alot of times exhaust systems that dont have flex sections built in allowing for movement seperate from the engine and chassis, it is crucial your exhaust have a flex section in it, usually closer to the end of the downpipe where the engine meets the rear motor mount as that is where the most movement will be seen whether forward or back keep in mind this is on a transverse engine car…FWD or most AWD) hanging off one end acting as a moment arm. Over time things fatigue. Perhaps the thicker material allows for longer durability. I am not sure. I am drawing correlations here but not causation. Correlations do not prove causation, we would need an experiment to prove this but I am using my personal knowledge and experience and things I have seen in my shop and other friends shops as a substitute for said experiment. (although I would love to perform one).
In terms of correlations. Turbo engines produce higher concentrations of heat in a manifold, thats not to say that a naturally aspirated engine wont make a header glow white, they will, but they are usually tuned soo ragged that they are on the verge of detonation. However. .065" 304ss tubing has proben to work just fine over time for the duration on naturally aspirated vehicles with little problems. Hell most mass produced muscle car headers are 1080 (mild) steel. Most naturally aspirated engines don’t see the kind of exhaust temperature that the average turbo car does.
Such material has been proven to stand up to the test of time in these applications.
Again one can only theorize that it is due to heat and heat concentrations built up in key areas like the collector (where the exhaust gas pulses merge). I am sure there is data somewhere to prove this but I’m not going to dig it up. That’s way more effort than I have put in now and I’m tired I’d rather show results than just pretend to know what I am talking about.
Alot of this is based on my personal experience over the years in the shop analyzing failures of components and plain and simple seeing what works and what does not. Not too mention talking to other colleagues in the industry (ie Magnus, Shearer, Burns Stainless, etc) and collaborating with other logical bright individuals (ie engineers of all types including Newman [love him or hate him he’s a bright guy with a mind for this kind of stuff]). We had spent soo much time on focusing on doing things right the first time when it came to everything but especially fabrication because not only does the part have to function properly but it is visual, you see that manifold or intercooler or piping etc it has to look good. I am not saying we were perfect. We have had our mistakes like anyone but again it has given us a world of experience and knowledge to draw from.
Hope in a round about way this helps answer your question.
Oh and one more thing. Stainless steel expands about 50 more times than that of mild steel when it is heated. Count that into the fatigue.
Yep, I appreciate the time that you spent. Cleared up a few questions that I had, and solidified any assumptions that I have made myself.
I definitely overlooked the added weight of the turbo to the exhaust manifold, and I see where it could be quite troublesome. Looks like its time to cut some springs and hit some pot holes lol…
