Ok guys and ladies....the topic is like this.

I was thinking the other day about the material used on fabricating manifolds.
So....please "show and tell" your opinions about the above.

 

sure, i'll play ball...

Stainless steal cons
-expensive

Stainless steal pro's
-won't rust

Mild steel con's
-will rust out
-needs to be coated

mild steel pro's
-cheaper

 

i would think expansion would be a side topic, mild steel would expand more i would think..

 

Mild steel has better heat properties than stainless... thats why mild steel is used for most head flanges on stainless manifolds.

 

i dont know about you, but i dont think ill even own my car long enough to rust through a SCH40 mild steel manifold!! haha.

 

Ok guys ....thanks for the input.

I think that stainless steel is more prone to haz cracking than mild steel due to the reduced intergranular corosion (more compact structure) which is destroyed during welding.

Mild steel is better in alot of ways....but I am not an metalurgist and I can explain step by step why.
So.....please feel free to discuss.

 

Search through some threads from Dave@Passenger, IIRC he has used mild with great results.

From what i can recall, a SCH40 mild manifold coated inside and out works out cheaper than a uncoated stainless manifold around here, and i'd put my money on the coated mild lasting longer, but thats just my opinion.

I can speak from experience that whenever I weld stainless runners off the jig they never line up quite like when they were just tacked, whereas with the mild i can do a set of runers with 2 passes and they usually line up pretty good when they go back together.

Also, the blade on the chopsaw lasts longer when cutting mild over stainless

Id go as far as saying that i believe mild is better than 304 stainless for making pipe turbo manifolds....

But take a look at some of the stuff you see on this forum, not naming names but alot of the sch10 stainless manifolds around here look like works of art, and i'm sure with the level of prep and full pen welds, good purge etc they are holding up pretty good.

 

Stainless looks beatiful only for a couple of hundreed miles than it gets burned and looks almost like mild steel.

I am sure that there's no scientific explanation to backup the fact that stainless steel (304 ...and the cheaper stainless alloys) is better than mild steel.

My honest opinion is that a mild steel manifold (let's say an S355 steel) will last longer than a stainless (without the common problems like HAZ cracking and hydrogen induced cracking)

But that's just my opinion!

waiting for more inputs.....

 

There is a reason that most high end manifolds are made of SS, Inconel or titanium. The reasons include better metal characteristics, including strength and corrosion resistance. Try to find a single high end source for mild steel manifolds. The only reason that flanges are made from mild steel is that it's much cheaper, much easier to machine, and much easier to flatten after welding, if necessary.

 

I will paypal $5 to the first person that posts a picture of a sch mild steel turbo manifold that has rusted through.

The coefficient of thermal expansion for stainless is roughly 1.5 times greater than mild steel. So if I did my math right a 15.75" steel head flange would expand .051" along its length vs .078" for stainless steel when heated from 41F-400F. Not sure if my calculations are correct.

 

For those in favor of steel runners.... look at the chart at the bottom of the below linked page and let us know how the steel characteristics in the chart better your header quality over stainless or inconel etc etc per our tempurature range (~1600F max). In addition, how many endurance race teams do you know running steel?

http://www.burnsstainless.com/stainlesssteel.aspx

 

Mild steel plus high temp coating ftw, if anyone says stainless looks better, I'll agree it looks better for about a month ( ok maybe a tad longer ) , after that they look like **** on a car.

Stainless cost more, is also rougher on tooling , and has to be back purged.

I tell people to coat everything now a days, not only does it look good and last a good while, it also keeps in the heat and helps make power.

 

So this manifold is all mild steel, then just jet hot coated? How is the cost effectiveness match up when you add in the need for coating though? The last time I checked it was pretty expensive to have parts coated.

 

I'm seeing a ton of people here saying mild steel is cheaper? I've always seen stainless weld els much cheaper then mild steel... Very odd, at 4.50-6$ a bend in stainless, why not?

 

If I buy locally at a industrial warehouse they have a few manufacturer choices. They are all ~$1.50 for a sch40 90 degree and ~$.90 for a sch40 45 degree. Super cheap.

 

Where is this place at? Everywhere I have checked wants an arm and a leg. Most local place to me aren't very cheap and I usually end up buying off the internet.

 

If you have a street car that sees all kinds of ups and downs in temps go with mild steel. If you have an expensive race car that only has high temps when driven at the limits go with the stainless or some kind of unobtainium.

 

There's no need for high stregth steel or extra high stregth steel in a manifold fabrication, because there's no force acting on an manifold.....the only considerent is heat resistance.....and Mild is better (intergranular speaking) than stainless on heat resisting.

Let's take for example an S355 steel (european norm type of steel) which is used for steam pipes and boilers....which needs to resist at approx 1300 Celsius degrees and an 1.4413 stainless (316 L) which at 900 Celsius degrees has majore alteration in the cristalin structure (such as cracks).

I think that S355 (steam pipe) witha coated finish is the way to....for any kind of use ...street or full race.

But that's only my opinion!

Cheers guys!

 

keep in mind that stainless steel has a MUCH LOWER coefficient of thermal transfer. It absorbs heat much worse than mild steel. this is a good thing and a great reason for ss.

 

It is a speciality place in Canada called amity industrial. If you try and buy the fittings from a place that only sells valves/fittings/caps/pipe it will be way cheaper. I tried general sources and they had prices close to what you listed. I don't even have a business account or anything I just occasionally go in and buy 20-40 fittings. You should you have a place like this near you.

 

On average, how much do these coatings generally cost?

 

Stainless steel is much better than mild steel

 

People use mild steel for head flanges for ease of machining and to reduce war-page. Sounds like you all just want an excuse to cheap out honestly. I get 304 1 1/4 bends for 4 bucks a piece. I wouldnt even know where to get mild weld els as i get them from a medical supply company that only carries sanitary grade stainless.

Bottom line, if you're gonna mig poop all over your weld el's and or not use a gas lense/ backpurge, then yea, you dont wanna poop all over stainless, it'll crack. But if welded by someone with their hands removed from their anus, its going to last longer, and be much stronger. Not to mention lighter since you dont have to use overkill city sch 40.

So a 40lb turbo, all sorts of high frequency vibrations, and the fanboy who's bottoming out the exhaust dosnt count as a force acting on the manifold?

 

According to the book "Scientific Design of Exhaust and Intake Systems" Stainless steel also holds heat better which keeps the exhaust a little hotter. Hotter Air is thinner and therefore takes less energy to move.

 

I'm not a metal expert and don't pretend to be but there must be a reason all pro mods, pro stock, and fuel cars all have stainless headers but they are also making 10 times the power anyone here is. I've seen nice carbon steel manifolds and nice stainless manifolds bu personally all the manifolds I've built have been with 304 ss from ace stainless. Relatively cheap, welds great, and holds up awesome