What's the exhaust made out of?

[chris82]

Does anyone know what kind of steel our stock exhaust systems are made of?

[Taskmaster]

http://en.wikipedia.org/wiki/Vibranium

[Joebie]

Many OEM exhausts are 409 Stainless. Not sure about BMWs though.

Definitely some sort of stainless alloy. You could narrow it down by seeing if it's magnetic.

[Dackelone]

Originally Posted by Joester

Many OEM exhausts are 409 Stainless. Not sure about BMWs though.

Definitely some sort of stainless alloy. You could narrow it down by seeing if it's magnetic.

The OE exhaust is mildly magnetic. I just tested what's left of my N55 mid pipes with a magnet.

[Jim621]

I'm not sure about stock exhausts, but aftermarket exhausts are definitely made of this stuff (unless they are made from stainless steel, or titanium).
http://en.wikipedia.org/wiki/Aluminized_steel

[chris82]

Originally Posted by Dackelone

The OE exhaust is mildly magnetic. I just tested what's left of my N55 mid pipes with a magnet.

Originally Posted by Joester

Many OEM exhausts are 409 Stainless. Not sure about BMWs though.

Definitely some sort of stainless alloy. You could narrow it down by seeing if it's magnetic.

According to Dack it's mildly magnetic, does that help?

[Iron Man]

Originally Posted by chris82

According to Dack it's mildly magnetic, does that help?

Ferritic/martensitic stainless steel, like 409, are magnetic. An aluminized coating on these steels could affect their magnetism some, but should still be magnetic.

Austenitic stainless steels, like 304/316 are not magnetic. 300 series stainless steels are typically more expensive to use, though have better corrosion properties and do not need any coating.

[tuphdc]

http://en.wikipedia.org/wiki/Inconel

[Iron Man]

Originally Posted by tuphdc

http://en.wikipedia.org/wiki/Inconel

I doubt any of the sheet metal sections are made from any Nickel based alloys in the 1-series exhaust (maybe some shielding parts?). Nickel is pretty damn expensive compared to steel alloys. I could see some of the fasteners maybe, but that is it. Where cost isn't as large a factor, yes, racing exhaust systems use it.

EDIT: The wiki page is somewhat wrong as well, since "Inconel" is a trademark name for the alloys, not really a class of alloys.

[3002 tii]

I'm assuming 409 given its tendency to rust and the fact it is magnetic. But it's definitely not aluminum or titanium.

[Dackelone]

Originally Posted by chris82

According to Dack it's mildly magnetic, does that help?

When I put my magnet on my tool box... it gets "attracted" to the metal very hard/fast. When I put the same magnet on my N55 mid pipes - the magnet just sticks there. But it doesn't have much pull or "attraction" to the metal, but it still holds/stays there. Does that make any sense?

[Iron Man]

Originally Posted by 3002 tii

I'm assuming 409 given its tendency to rust and the fact it is magnetic. But it's definitely not aluminum or titanium.

409 is a ferritic stainless steel. It is coated with aluminum to help corrosion properties.

[3002 tii]

Originally Posted by Iron Man

409 is a ferritic stainless steel. It is coated with aluminum to help corrosion properties.

I've had 2 different 409 ss exhausts develop rust. The piping was nice dark orange while the 304 muffler and tips remained shiny.

And when I said NOT aluminum nor titanium I wasn't referring to coating but the predominant metal.

[Iron Man]

Originally Posted by 3002 tii

I've had 2 different 409 ss exhausts develop rust. The piping was nice dark orange while the 304 muffler and tips remained shiny.

And when I said NOT aluminum nor titanium I wasn't referring to coating but the predominant metal.

Yes, I know. I was just adding more info to your post. 300 series stainless steels like 304/316, have much better corrosion properties than 400 series stainless steel. 409 is comparatively cheaper, and that is part of the reason why it is used, though, as you experienced, it will never outlast a good 304 exhaust.

[3002 tii]

Originally Posted by Iron Man

Yes, I know. I was just adding more info to your post. 300 series stainless steels like 304/316, have much better corrosion properties than 400 series stainless steel. 409 is comparatively cheaper, and that is part of the reason why it is used, though, as you experienced, it will never outlast a good 304 exhaust.

Sorry I thought you were making the point the aluminum coating keeps 409 rust free. We are on the same page.

[The Wind Breezes]

Originally Posted by Iron Man

Nickel is pretty damn expensive compared to steel alloys.

I wouldn't be surprised if the turbofold has high nickel content. The turbofold for the Golf R K04, for example, has a bunch of nickel. I found out that out while researching why it was so difficult to hand tap that manifold for a NPT threaded EGT probe. The nickel makes the whole assembly way more resilient.

[Iron Man]

Originally Posted by The Wind Breezes

I wouldn't be surprised if the turbofold has high nickel content. The turbofold for the Golf R K04, for example, has a bunch of nickel. I found out that out while researching why it was so difficult to hand tap that manifold for a NPT threaded EGT probe. The nickel makes the whole assembly way more resilient.

300 series stainless steels, like 304 used in exhausts, do have high Nickel content.