What kind of material should be used for a turbo setup? Is coated mild steel fine or will the inside flake and break the turbo? Is stainless absolutly beyond all else neccessary?

 

I found Corky Bell's book on turbocharging very useful for stuff like constructing a homemade header or turbo kit. It's called "Maximum Boost" and you can find it cheap at Amazon.com. Talks specifically about header flanges, metals, and other points.

I believe Corky states that mild steel would be acceptable, with modern ceramic coatings, for the heavily loaded turbo header and wastegate mount.

Jim

 

coated mild will work fine, also 321 stainless, 304 will tend to crack more

 

Coated Mild works.. there is a lot of debate on coating the inside of the tubing. The arguement against is that the coating could flake off and damage the turbo. The flipside is that if you are using mild... the inside WILL rust and then you get rust flaking off into the turbo. So, your damned if you do and damned if you don't if you are using mild. 304 prevents the flaking issue, but a lot of people complain of cracking with 304 manifolds. 321 is more resistant to cracking, but it starts getting $$ Same goes for inconel, awesome to use... but $$$. Ideally, at our level, 321 is what you want to use... but it really comes down to if you can afford the extra expense. Mild works fine, and the whole rust/coating flaking issue really is more an academic debate because as much as it is debated... it isn't something you really hear about happening a whole lot. Everyone will tell you it's a problem... but try to find someone who actually fragged a turbo due to rust or coating flaking off... they are very few and far between... even though there are a ton of mild manifolds used in kits.

 

the pics I've seen of cracked 304 had one piece header flanges. the cracks suggests the metal is stressing out due to heat expansion. max boost specifically points out you need to plan for this expansion with oblonged bolt holes and and perhaps individual flanges for each exhaust tube. a proper fitting union between flange and tube along with smooth, stress free welds should go a long way to extending the life of 304.

 

Mild steel is the best way to go for the money. All will be equal in strength for a street car as long as you brace the turbo and the rest of the turbo system.. Anyone who tells you about their headers cracking due to poor material are morons for not bracing their turbo system correctly and letting the entire weight of it sit on the headers.. The best material though for all out performance is called Inconel- 1800*F fatigue strength but is very difficult to weld and very expensive.
The best way to connect the headers to the hot pipes is using slip-fit style connectors. Using bolt-on flanges will work but put added stress on the system for not alloing much flex..

 

Okay, settle down there Skippy... There are obviously many factors involved with turbo header design that contribute to both performance and durability. The question asked has to do with material selection, and the fact that 304 does not have the high temperature fatigue resistance that 321 has is a fact. Not saying that a poorly designed 321 setup won't crack or that a well-designed 304 or mild setup will definitely crack... just saying all else being equal, 321 is less likely to crack than 304.

 

Just for conversation. How many of the six people that have replied above have owned or built a turbo system?

I have not owned or fabed a turbo system yet so don't think I am *******, I am just trying to weed out the " I read it some where and I think I can post about it now" syndrome.

Smokin, I know you are fabin your own kit.

Thanks.

Tim

 

Here are my headers. I used all 321 stainless. So far they are holding up excellent and are a nice golden color after heated.

 

I've fabbed several headers and hot pipe kits for different people, including one for myself which I will be constructing completely out of Inconel tubing whenever I get around to it..

 

Sweet, actual first hand knowlage.


The more I read in this forum the more I sit here and think about the people posting are saying to themselves "I don't have anything better to do but to read **** and then post **** I read like I know what I am talking about, even though I haven't done it."

You know who you are!!!!

Thanks.

Tim

 

Yup, its called bench racing- people sit on these forums and read what other people are doing/screwing up.. Then they go out and run the same product that got all the attention on these forums and claim they knew it would be the best setup all by themselves..
Im a trial and error guy- i know half my **** wont work the first time, but at least I know it first hand and know the results and what went wrong. I know some of my headers will fail due to workmanship- it happens to everyone..

 

exactly, its not like i won't use other people's ideas ( I'm an idea ***** ) on my car but I also don't post about the setup like I came up with the idea myself.

Tim

 

ya, raises hand.
on my turbotech kit i had my 304 stainless log coated inside and out, it never flaked off. it cracked a few times though. This time im going with cast manafolds, no cracking now

PTK has always used mild coated, they have released a LOT of kits, and can anyone find someone with their kit that has cracked, or the inside has flaked off and ruined a turbo?

321 with slip fit would be your best bet, nobody can argue with that.
Cast is good as well for its properties, but your limited to the incon and stock or truck manafolds

 

My friend and I fabbed a setup for his 3rd gen using banks manifolds... Most of my friends in the local car scene are turbo guys though... and since I have a lot of fabrication experience whenever something good or bad happens, I tend to be one of the first to hear about it... Plus I worked in a machine shop while I was in college and spent a few years after that working on race cars... so I'm not exactly a bench racer... I have personally welded all of the materials we have been discussing including Inconel.

 

Smokin and TchargedLS1TA
know what they are talking about...


TchargedLS1TA he is currently in the process of fabbing up my new set up using 6.0 manifolds! YEAH!

 

Can I ask how much you paid in materials for those.

 

304 headers are fine as long as they are backpurged, and again, the turbo is mounted properly and/or you have THICK weld Els that can take the abuse.

Inconel is not hard to weld, It always looks like a dirty pool, but it just welds so seamlessly. Its really unique. Ti is the same way to an extent

 

For the record I was planning to but I wound up buying an Incon car fully assembled and tested I am an experienced welder and have read a lot of material on building headers and, oops, I meant to post that disclaimer...

Design is as important as material. Proper welding technique and turbo support are mandatory. IIRC, 304 expands a lot more than mild steel so you have to be sure there is proper tolerance built in to bolt holes...

 

I started thinking about this question this morning after my last response... what you probably want to do when looking for "good" information regarding a topic of this sort is focus on getting advice not necessarily people who have owned turbo kits... but material experts such as certain types of engineers or experienced Machinists/fabricators. If your relying solely on first hand experience with kits... you can get an answer that was derived from a poor deduction of the problem. I.E. A lot of CAS manifolds have cracking issues... I'm sure that some people would say that is because it was made of 304. The FACT that 304 doesn't have the high temperature fatigue resistance of 321 is probably a factor... but the more important factor is the fact that it is a log style manifold and that (based on pics I have seen) it does not appear that the welds were properly backpurged. Had it been made of 321 but the design & fabrication remained the same... it would be more resistant to cracking, but ultimately, would probably still crack. Likewise, the theory only gets you so far... theoretically mild steel sucks because no matter what you do, you will either get rust or coating flaking into the turbine wheel. Taking theory out of the picture... I have personally only ever heard of one third hand account of a coating flaking and taking out a turbo... and considering the sheer number of turbo cars I have been around over the years... I feel that is pretty remote. As with anything on-line... you kinda have to take everyone's information with a grain of salt... take the arguments, weigh them for yourself and do what makes sense to you. Going back to the original question:

The flaking issue was covered. And the advantages and disadvantages of the 2 common alloys of stainless was also covered. As for the issue of Inconel... It is a very trick metal, but even for a tech-weenie like myself... I'd be really hard pressed to justify Inconel headers on a street car.