Evening all!
I was wondering if I can pick your brains, and see what knowledge you all have on this stuff.

I'm currently doing a little /2000 word document on Exhaust Manifolds and I'm wondering about what materials and processes are used in casting for production manifolds.

Also, for tubular style manifolds (performance exhausts) and what are the materials used in those? Deffinately not iron that's for sure! Some kind of Steel alloy?
Nickel?
Manganese?

Sand casting is one of the things i was thinking about but i'm not sure it's appropriate. What other forms are there? Die casting... too OTT for a basic part....

I'll stop now as i'm waffling, i'll step back and see what you know

I think headers (as tubular exhaust manifolds are called here in the US) are typically made of steel. Maybe aluminium too, but I'm not sure about that. For more common manifolds, I think iron is most often used. My 1994 Pontiac Bonneville (3800 lb FWD boat, pushrod 3.8L V6) had iron exhaust manifolds.

That reminds me, the exhaust "manifold" on my bike (in quotes because it's just a single pipe, due to only 1 cylinder) has a golden color to it. I'm not sure exactly what type of metal that would be. See here:

http://www.bikez.com/motorcycl ... -g6_super_sherpa_2002.php

Better pic here:

http://www.off-road.com/dirtbi ... gallery/sherpa_studio.jpg

What about racing manifolds, especially up into the LMP and F1 ranks? Surely they'd be a lighter material?

Usually exhaust manifolds are typical die cast iron with above 2% carbon.
In racing you can find higher quality exhaust manifolds with heat resistant steel alloys, typically with chrome and nickel, if I didn't forget too much about steel.

Vain

doesn't a steel/copper alloy have a golden colour to it? or is it steel/nickel. Or was it........ so many types, you get lost!
I've found out in say, formula one, the exhaust length is determined by what RPM they want the engine to perform best at. It's a comprimise part... But the exhaust isn't the issue, it's the manifold (going off the rails again)

Quote from Forbin :

I think headers (as tubular exhaust manifolds are called here in the US) are typically made of steel. Maybe aluminium too, but I'm not sure about that. For more common manifolds, I think iron is most often used. My 1994 Pontiac Bonneville (3800 lb FWD boat, pushrod 3.8L V6) had iron exhaust manifolds.

That reminds me, the exhaust "manifold" on my bike (in quotes because it's just a single pipe, due to only 1 cylinder) has a golden color to it. I'm not sure exactly what type of metal that would be. See here:

http://www.bikez.com/motorcycl ... -g6_super_sherpa_2002.php

Better pic here:

http://www.off-road.com/dirtbi ... gallery/sherpa_studio.jpg

This might sound a litte odd coming from a guy in New Zealand.
Yes, the 3800 engines come with the Iorn Exhaust manifolds. I have been around soo many of those engines. One in my moms minivan (1995 Chevy Lumina LS 3800) one in my dads Fiero GT and 2 spare ones in the garage (one Series 1 S/C and one Series 2 S/C)
Hehe, those Bonnevilles do prety darn well if you have a S/C engine. Not sure which Series 1 came in the 1994 but some are almost S/C ready and others are just the plain 3800. All my moms minivan requires for the Supercharger is the Supercharged style heads.

Well, away from those engines....
From what I have seen most cars come with iorn headers. I have not seen any header made out of aluminum but that does not mean they don't exist.

My dad made his own performance exhaust from the headers all the way back and used the Tubular steel exhaust pipes. They were the more expensive type that had the smooth curves but I am not exactly sure what they were.

@Motorbike:
It's propably a nickel-chrome-moly steel. Like those fancy racing-thingies.
@Aluminium manifold:
Those things heat up to 800°C. (Pure) Aluminium melts at some 650°C.

[Edit]
After some more research I can also offer nickel-basis alloys. Nickel-chrome-aluminium alloys (~75-20-5) are also used in aircraft turbines.

Vain

Quote from Vain :

After some more research I can also offer nickel-basis alloys. Nickel-chrome-aluminium alloys (~75-20-5) are also used in aircraft turbines.

That's some interesting information, thanks

@skstibi: My 3800 was the plain naturally aspirated one and it saw redline almost daily until the day an electrical problem caused the fuel pump to malfunction* . The engine ran strong the entire time, though.

*was actually an ongoing problem. Once in a while the car would just stall while moving, as if it had run out of gas. I'd pull over and usually it would start again on the first try. However, there was one occaison where it didn't start for about 5 minutes.

According to my notes, Nickel-Chromium heat resisting alloy of 80 - 20 resists oxidation at temperatures around 1000C. But I don't think they'd use such mixtures for the manifold. We're not just talking about singleseaters, but touring cars, anything racey...

Vain, you seem to know your stuff! :P

Quote :

Vain, you seem to know your stuff! :P

German engineering for teh win!

*Goes and unpimps some auto*

Vain

I was going to suggest Titanium as a good material, but then I remembered it has oxidation problems at high temperatures. Not good for a manifold.

I'd guess some sort of cromoly steel, as has been mentioned. That's pretty much the standard material for high performance applications.

Ok great! So how are they created?

Quote from Forbin :

I think headers (as tubular exhaust manifolds are called here in the US)

Header and tubular exhaust manifold are in my experience two different things as referenced in the US.

My Jeep came with a cast tubular exhaust manifold that like most examples failed in short order. I replaced it with a header made by Borla from drawn over mandrel stainless tubing mandrel bent and welded together. Good headers for street cars are made from something like 321 "stainless". Later in the exhaust path (like cat back) 304 stainless is adequate. Fancy race cars use pure unobtanium, or something barely obtanium like Inconel.

The big problem with cast tubular exhaust manifolds is that cast parts with relatively thin walls and long tubes are bound to crack. The Jeep manifold is about three feet long, and the weight of all six exhaust tubes, the collectors, and the downtube to the cat is suspended from one flange. On newer engine designs they make more sense, like a 4 cylinder with a close coupled catalytic converter.

Quote :

Maybe aluminium too, but I'm not sure about that.

Oh hell no. Any aluminum based alloy would be a puddle on the ground.

Quote :

That reminds me, the exhaust "manifold" on my bike (in quotes because it's just a single pipe, due to only 1 cylinder) has a golden color to it. I'm not sure exactly what type of metal that would be. See here:

Probably what Vain said, a "stainless" alloy of sorts. There is a process by which the austentitic stainless steels turn gold after heat cycling, but I can't remember exactly how it works. One of the alloying elements migrates towards the surface. This is why when you buy shiny silvery stainless exhaust headers they turn gold in short order when exposed to hot exhaust gases.

Quote from 5th Earth :

I'd guess some sort of cromoly steel, as has been mentioned. That's pretty much the standard material for high performance applications.

Here in the US at least we generally refer to "chromemoly steel" when talking about alloys like 4130 and 4340 or 300M. 4130 is what you build high performance tubular steel structures from, but I've never heard of anyone using it in an exhaust. 300M/4340 are the alloys people build things with really high levels of reversing stresses of, like halfshafts. 4340 has some nickel, but practically none compared to say 321 which also has niobium/titanium as a stabilizer. The chromemoly alloys probably aren't used because the "stainless" alloys maintain greater corrosion resistance and strength at very high temperatures.

Quote from MR_B :

Ok great! So how are they created?

Get tube, bend tube, weld tube.

@Welding: Not if it's die cast iron. Try to bent die cast iron and you've got two parts of die cast iron. But no manifold.
Those steel manifolds can be welded

Vain

Nooo, i mean what's the process for making one of those (attached pick) I figured the tubular manifolds are welded :P :P

There are various methods to cast a manifold.
If someone would ask me I'd suggest a foam model in magnetic mold material. Place the foam model in the material, fill it with some more material from the inside, activate magnetic field, magnetic material becomes hard, pour the molten iron into the form, foam model vaporizes, iron fills the now available space, wait for it to cool down, disable magnetic field, mold material looses cohesion and voila, grab the manifold and you're done.
But then again, I'm not an employee of any manifold producing company, so better don't ask me. The process I just suggested is propably by far too expensive. Also there are a lot more things to be considered and the way of economically casting manifolds is partly the know-how that makes a company successful.

Vain

Quote from skiingman :

Here in the US at least we generally refer to "chromemoly steel" when talking about alloys like 4130 and 4340 or 300M. 4130 is what you build high performance tubular steel structures from, but I've never heard of anyone using it in an exhaust. 300M/4340 are the alloys people build things with really high levels of reversing stresses of, like halfshafts. 4340 has some nickel, but practically none compared to say 321 which also has niobium/titanium as a stabilizer. The chromemoly alloys probably aren't used because the "stainless" alloys maintain greater corrosion resistance and strength at very high temperatures.

Fair enough. I confess pretty much all my materials experience is from battlebots, where aluminum and titanium are the rule (along with high-strength plastics and carbon fiber/kevlar composites, and a smattering of magnesium). Steel is relatively rare--usually just S4 tool steel, which you obviously wouldn't make exhausts out of.

So I don't know much about it. Funny, really--I know a lot about the "exotic" materials, and very little about basic steel.

Quote from MR_B :

Nooo, i mean what's the process for making one of those (attached pick) I figured the tubular manifolds are welded :P :P

Foundry methods are still at least part art, and much of the information is proprietary to that industry. Sort of like tires.

http://www.casting-source.com/casting-chart.htm

The ugly tubular header on my Jeep was almost certainly cast using one of the sand casting methods. When you look at something much prettier like the pic you posted its probably produced using some fancier methods.

Check out this page describing the design, prototyping, and production of a turbo exhaust manifold:
http://www.flyinmiata.com/projects/new_turbos.php

Well, my coursework is done. I was up until 5am finishing the document, and i'd like to thank you guys for your help and links.

A very helpful read is a book called "Fundamentals of Modern Manufacturing" by Mikell P. Groover.