View Full Version : turbo headers, exhaust systems and stainless steel
I am looking for everything I can click my mouse on regarding turbo header design/fabrication, exhaust system fab and stainless steel fabrication in general
I'm almost confident I could successfully complete my project with my trusty Hobart 135 MIG, but am seriously investigating the purchase/learning curve of a TIG (likely a combo TIG/Stick/Plasma Machine)
Any links/advice is greatly appreciated,
and I have a couple specific questions I'm hoping to find answers to:
First, I'm hung up on what to use, Burns Stainless suggests 16ga or even 18ga! yet a large majority seem to use schedule 10. what are the advantages/disadvantages of both?
Second, I plan to use 304 Stainless, but would like to use 321 and/or possibly Inconel in a few key areas.
How and with what do you weld these different materials together? And is this a bad idea for someone with limited experience?
09-29-2008, 12:29 AM
I can't see adding inconel into the setup for any reason. As for the header materal, the thicker material is more forgiving to work with, and will take bends with less issues. That would be the primary reason for going with the thicker material, especially with a turbo. More heavy heating cycles, and the material can have cracking issues.
A mig will do the job, it just won't be as pretty. But, conversely, if you are not experienced with building headers, the mig will be a much more forgiving machine. Tig will require very tight fitment of parts, and there is a lot of chances for burn thru on the tubing ends. Also, if you have a gap, mig will fill it much more effectively than a tig machine. Stick to 304 tubing. You will have a heart attack when you see the cost of exotic tubing; and it is not necessary.
09-29-2008, 01:00 PM
Yes GMAW process can do the job a 135 will not.
Thicker is better for everything bolted to the head and the turbo. I use sch 40 321 pipe. I use 1/2" 321 for the flanges. I surface grind them after all welding is complete. Everything down stream of the turbo can be thinner, the further away from the heat the thinner you can get.
If you are building a F1 car then you might consider inconel (sp)
09-29-2008, 03:38 PM
Welding stainless with a 110V MIG almost impossible and the tri mix gas will cost a lot.
The best process with the most control will be TIG.
I would use .065 wall tube or thicker.
Sceduule 40 pipe??? WOW !, it will weigh a lot.
09-30-2008, 09:22 AM
huh, what, huh
09-30-2008, 12:58 PM
There are tradeoffs- what material is best will depend on who you ask. I honestly don't know.
What I do know is that you should take anything a vendor tells you with a grain of salt.
In other words, if I was in the business of selling material for exhaust header manufacturing, I would be tempted to exaggerate the benefits of higher grades of stainless when they are twice as much money. Why would I tell people that the cheaper stuff works fine?
I'm not saying there isn't a case for 321- maybe there is.
Here's the few things I do know:
1) Bracing seems to work. Partially because it is removing the weight of the turbo, but more because it damps the vibrations. Resonance and engine vibration is really hard on parts. People overestimate the heat aspects and underestimate vibration/fatigue issues IMO.
2) That said, brace the manifold sensibly. Don't just weld big solid bars all over it- the manifold needs to "breathe"- to expand and contract some with heat. But do brace it.
3) Starts and stops are critical. Craters are cracks, waiting to be born.
4) Use as little current as possible to get the job done.
At the end of the day though if you really want to work with stainless consider picking up a cheap DC only inverter tig such as a miller maxstar.
It will have plenty enough power for stainless exhaust work and many will run off of a 120V outlet.
09-30-2008, 01:34 PM
Remember that Burns Stainless deal (or appear to) primarily with race applications- weight matters!!
Forget inconel, it's a pain to work with, horrifically expensive and unecessary for most applications. For street use stick with 304L, for now at least (it's available everywhere and is relatively cheap) as the temps generated are going to be a lot lower than in a race car. I'd love to build myself an inconel header with Ti system and box but unless i win the lottery it ain't gonna happen- yes i could save a bunch of weight but on a road car... pure overkill/indulgence
Obviously exact application needs to be considered but Sch 40 is overkill IMO. Doesn't matter what it's made from if it's made badly...
Personally i use 16swg 304L for most things, sch10 would be a bit more forgiving
Schedule 40 is pretty common among the DIY crowd, but mostly in mild steel, and that's mostly because of its price/availability. Naturally aspirated 18 gauge (.050) would be fine, but is a bit on the thin side for turbo apps, and with cheaper stainless, you'll see it break down pretty rapidly from the heat cycles.
Schedule 5 pipe at header sizes have .065 wall, with schedule 10 being .109 wall. You may want to factor this in to match according to your exhaust ports. For example, NPS 1 1/2 schedule 10 will give you an ID of about 1.79, close to a common 1 3/4 header tube.
If you don't plan on backpurging the system as you weld it, I wouldn't attempt it with anything less than schedule 10. Unless you're well versed in welding on thin stainless, you'd get a ton of sugaring on the inside of the pipe. Not to say you're not going to get it with .109 wall, but you're definitely going to get it with .065,
09-30-2008, 03:16 PM
If you don't plan on backpurging the system as you weld it, I wouldn't attempt it with anything less than schedule 10.
I think this is partly why sched 10 has gained popularity for this application- you can get by without a backpurge.
16ga will need a purge, it is less forgiving when it comes to gaps in the weld joint I agree, but it is also a heck of a lot easier to fit up well, since it's easier to tweak the fitup.
Also cuts faster. So it's probably a tradeoff, maybe even nicer to work with if your layup/fitup skills are good and you have a simple backpurge setup. Coping the .109" wall stuff takes quite a bit more grinding.
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