OEM exhaust manifold header material

[krashdumie05]

Anyone know what material the oem headers are made of? I’m going to cut out the cats out of the headers and weld in a straight section for a cheap set of Catless headers

[Slideways]

"All metal components in the entire exhaust system are made of high-temperature resistant austenitic stainless steel. Thanks to its high corrosion and acid resistance, the durability of the exhaust system has been extended to match the car’s life expectancy."

Some reading material - http://www.unofficialbmw.com/images/...ust_System.pdf

[PSUEng]

Ah, the Arvin Meritor presentation on the stock exhaust, great info in that. I will give it to AM for their engineering and I think the stock system is very good but, having my full SS V1, I have no regrets taking the stocker set off. And I do think the material selection would in fact result in the system lasting a long time. But damn, that section 3 is like 50lbs, no wonder the rubber mounts failed!

[timmo]

Wow! Indeed a great technical document, I wonder if any others exist for the E46?

[digger]

it doesn't appear to be 300 series maybe it is 200 series but still 308 filler material seems to be the recommendation for welding to 304

[bigjae46]

I think it’s a 409 stainless alloy. I think 308 wire will work. Should also back purge the weld.

Thats why you get the Megan Racing headers.

[digger]

I think it’s a 409 stainless alloy. I think 308 wire will work. Should also back purge the weld.

Thats why you get the Megan Racing headers.

409 is not austenitic so would conflict with the document above

[NZ_M3]

It’s 304 for non CSL

[Turboixxi]

apologies for bringing back an old tread but just wanted clarification. If the Euro non-CSL is 304 or 310 stainless steel, what is the CSL version made out of?

I've noticed CSL lambda sensor bungs have been broken on a few and was either repaired or needed repair. Does the standard Euro exhaust manifold also have this issue with the lamda sensor bungs breaking? or is it just the thinner type of steel used on the CSL version?

Are there any other issues with euro/csl headers?

[mpower22]

Actually bigjae46 is right. I am an original owner, on the waiting list for 2 years back then and I can tell you that the referenced document above is very old and came out when the E46 M3 was still in development. The final decision was revised to use 409 stainless steel. This is the case for the NA, Euro, and CSL versions of exhaust. 409 is less expensive because it has a higher iron content, but it also handles heat cycling better, specifically at the welded joints. As some may or may not remember, back in the 2000's almost no manufacturers used 304 stainless on high-heat/high-stress exhaust sections. Reports of broken welds on 304 exhaust were not uncommon on any random model car forum.

However, although more corrosion resistant than a standard steel exhaust, the higher iron content makes it more prone to rust, especially when exposed to moisture at high temperatures. This is why almost every set of used Euro headers or cats you see online show a significant amount of rust. 304 stainless will not rust that easily and will typically only rust if constantly exposed to salt water, chlorine, or a similar corrosive chemical; but the key there is constant exposure.