Choice of materials for exhaust manifold.
 

I am wondering why you guys are using stainless steel?Mild steel will give you guys better results for longevity and easier for non pros to work with.I personally use mild steel on all log manifolds.

Re: Choice of materials for exhaust manifold.
 

it depends on the budget... :y

Re: Choice of materials for exhaust manifold.
 

sched 10 stainless els on everything.

mild steel isnt any cheaper so why ever use it.

Re: Choice of materials for exhaust manifold.
 

Because to weld stainless properly it should be back gassed.

Stainless expands and contracts much more under heat than mild steel.

Machine tools suffer while cutting stainless steel.

Mild steel manifolds last longer.

Re: Choice of materials for exhaust manifold.
 

but if you havent noticed, noone gets a hardon for mild steel, its not jdm.

im setting up my backpurge tank monday.

remember its gotta be jdm yo, or noone wants it.

Re: Choice of materials for exhaust manifold.
 

Is leaking out the #1 and #4 runners JDM?Building log manifolds also leads to banana shaped head flanges and pulling out of head studs.

Re: Choice of materials for exhaust manifold.
 

maybe for you it does, i have a surfacing tool *if a flange happens to warp, but i havent had to use it yet. my plates that i weld to do th etrick nicely,

and i have triple check every manifold and have never had a leak, crack or anything of that nature.

Re: Choice of materials for exhaust manifold.
 

You will start having problems.The manifold warps after being heat cycled on the car.It will start with a leak when cold and then seal itself up when hot.Eventually it will ---- out the gasket and then it never stops leaking.

If you are questioning what I know,I have been doing this for a while and was once at your level.

Re: Choice of materials for exhaust manifold.
 

Stainless steel retains heat approximately 30% better than mild steel. This makes for faster spool times on turbo manifolds and less engine bay heat for all cars. Stainless steel is overall just much stronger.

Stainless steel doesnt need special gasses. However because it expands much more under heat, it makes it even more crucial for welds to penetrate 100%. Thats pretty easy to take care of though.

The one thing you don't want stainless steel for is in the header flanges.
Because of the expansion, it can pop off the nuts destroying the studs and cause all kinds of nasty stuff.

At the current cost of steel, SS is barely more expensive than mild for our application.
Even if it was more expensive, the performance gains and strength would still be worth it.

Re: Choice of materials for exhaust manifold.
 

So are you trying to say that this makes a difference in a log manifold?Not that it matters because I use sch40 material with is much thicker.

It does not take special gasses to weld stainless,but it does take proper technique to weld with is time consuming and costs money(unless you want brittle welds with big carbon chunks inside your manifold ready to break off and destroy your turbo).

Its the extra expansion and contraction that causes manifold failure.When the log expands and contracts it causes nuts to start to loosen up and causes a host of other problems related to expansion.

Most of these problems are reduced in equal length manifolds because of the load being ------ out over a greater area.

Re: Choice of materials for exhaust manifold.
 

Anyone who is buying a log manifold obviously doesnt care much for flow and is looking to save money, so yeah I would just use mild steel.

I actually find it easier to weld stainless because of how the heat stays very centralized. With some good prep work and a back purge, you will never get any sugaring on the inside of the tubing. If you dont prep your material the exact same thing will happen with mild steel.

Read my previous post. DONT USE STAINLESS STEEL FLANGES. Even if you do use stainless steel flanges, think about it. A lot of nuts and bolts nowadays are stainless steel. Therefore, they will expand with the flange.

The log can go through 8234237 heat cycles and nothing will happen to it as long as all of the welds penetrated all the way. Explain to me what would cause the log to fail if all the welds have fully penetrated. Do you think that mild steel doesnt expand? Mild steel expands a shitload too, just not as much as stainless steel.

Re: Choice of materials for exhaust manifold.
 

The log is expanding at a different rate than the head which leads to movement at the head be it either lov vs flange or log vs head.If you dont cut between the runners the manifold will turn into a bananna,if you do it will constantly loosen the bolts at the head.There is no way around this.

Re: Choice of materials for exhaust manifold.
 

Yeah but the head is aluminum, so how does mild steel help?

Re: Choice of materials for exhaust manifold.
 

The head is liquid cooled ;)

Re: Choice of materials for exhaust manifold.
 

Don't the outer ends of the manifold compress harder against the head when the manifold is heated up? I think I recall this is why the old V8's exhaust manifolds get lesser torque settings on the hardware in these areas than the hardware in the center of the manifold.

Is this the "bannana effect" is wich you're referring to?

Re: Choice of materials for exhaust manifold.
 

Still not buying it.
I can heat aluminum by pissing on it.

Re: Choice of materials for exhaust manifold.
 

im not questioning what you "know" i am just telling you my real world experiences.

people have been running manifolds for a long time, and ive never heard of or seen a problem. i know guys with flux core miggedlogs that have been going hard for years.

stainless all the way for me.

the price difference doest warrent the use of mild steel ever.

i have used quite a few stainless head flanges as well, also with no problem.

Re: Choice of materials for exhaust manifold.
 

All of what Slappy says makes sense. The fact of the matter is I have seen and built quite a few manifolds and some have been in heavy use for years with no problems. I guess if you intend on running really lean and high exhaust temp for 10 years then you may have an issue. Honestly how long do most guys run a manifold for?

Re: Choice of materials for exhaust manifold.
 

2 weeks

Re: Choice of materials for exhaust manifold.
 

Till his nuts drop ;D j/k.

Alot of the 1.9t VW guys(elitist pricks :P) have alot of problems because they run high boost and extremely high EGTs.

Re: Choice of materials for exhaust manifold.
 

Yeah, like CS said, what you're saying makes sense.

Re: Choice of materials for exhaust manifold.
 

How much do your mild steel elbows cost you?

Schedule 40, 304 Stainless Steel Elbow - 45605K515
$5.89

Re: Choice of materials for exhaust manifold.
 

theres ur first prob, sched 10 stainless els i get em for 4.25 a piece.

mild steel is just flat out not worth it. people arent willing to pay anything for a mild steel mani, evwen though it costs just as much to make.

Re: Choice of materials for exhaust manifold.
 

My time is worth something,and machining stainless steel costs time and machine tools.The other option would be to take the plasma cutter( a real plasma cutter BTW) and blow crap all over inside the manifold.This in turb peels off and gets blasted through your new turbo.

SCH 10 is half as thick as sch 40.If you have a big enough welder you can lay in a much stronger weld.

Re: Choice of materials for exhaust manifold.
 

you dont get slag in the mani if you take a few minutes and make some sheet metal shields for the runneres ect.

tinfoil also works good.

thwe siley plasma cutter burns through sced 10 like butter.

Re: Choice of materials for exhaust manifold.
 

I agreed with everything you said above except for the last statement. Its proven fact that mild steel has a greater percentage of lost material through the course of heat cycles.

Re: Choice of materials for exhaust manifold.
 

I would love to see this tin foil operation.

Re: Choice of materials for exhaust manifold.
 

At the shop I work at, we'll make about 2000 cuts on one bandsaw blade.
They are supposed to last over 3000 cuts, but we punish the saw and use lots of SS for some production projects.

The blade for our Ellis costs about $70.
If we only cut mild steel, that blade would cost about $40.

So for stainless our price per cut is about 3.5 cents and for mild it would be about 2 cents.
I'm going to guess you make 25 cuts per manifold.
That comes to a total savings of 37.5 cents.

Conclusion - By using mild steel you save 37.5 cents per manifold to cut.

Re: Choice of materials for exhaust manifold.
 

ill take pics.

Re: Choice of materials for exhaust manifold.
 

Sorry to bring this back from the dead but i have been doing some research on this topic and found some good info.

http://www.burnsstainless.com/TechAr...s_article.html

Its a really good article and if you know anything about thermal equilibrium diagrams you might get a little more out of it. At the bottom it shows the modulus of expansion for mild and stainless steel and mild is 7.228 while stainless is 9.9 so it doesnt expand that much more. Also if you look at the thermal conductivity you can see that stainless is a much better choice for a manifold since you want to keep the heat in so you can keep your velocity up.

Re: Choice of materials for exhaust manifold.
 

i was hoping id never see slappynuts name again.... damn you ------

Re: Choice of materials for exhaust manifold.
 

lol, watch it with the "------" comments josh, some ethugs may take offense.

Re: Choice of materials for exhaust manifold.
 

Why because he can post logical arguments and back himself with pictures?
Post pics of your cracked sleeves... ------.

Re: Choice of materials for exhaust manifold.
 

no, just because hes a fat -------. no other reason

Re: Choice of materials for exhaust manifold.
 

so let me get this stright, for a header design, log, ramhorn or what have you, all stainless is better? Or would it still be sufficient to have a mild steel flange?

Re: Choice of materials for exhaust manifold.
 

i use mild steel flanges and stainless runners

Re: Choice of materials for exhaust manifold.
 

hotrex: lol, u said stainless all the way... thanks for the insight.

Re: Choice of materials for exhaust manifold.
 

First he was acting like the student in his first post then he acted like he was the ------- professor. Why ask for something if your then gonna like your already know the answer? :-\ Mild steel manifolds make baby Jesus cry.