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What is the most durable, long-life material for exhaust systems? I assume this is probably stainless steel, though even for that there are different grades of the metal.

When looking for aftermarket exhaust components, is there some way that long-life / part durability is described without talking about "engine performance"?

Dale Mahalko
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  • The ferritic stainlesses commonly used today are an excellent choice. As noted , unobtanium would likely be the only improvement. – blacksmith37 Dec 02 '17 at 16:11

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300 "austentitic" series stainless, specifically 309S, 316 or 321.

All have higher levels of chromium and nickle, for ultimate corrosion resistance. 321 adds titanium that improves thermal stablity at higher temperatures. 309S is rare and contains more chromium, but is often used in high heat applications.

Be prepared to empty your wallet, because any truly outstanding exhaust material is an alloy of expensonium and unobtanium...

Aftermarket manufacturers tend to shy away from accurate desciptions of the material composition, because the majority get away with "stainless" (which is true to a point) but hides the cheaper nature of the material typically used. Certainly by no means is all "stainless" created equal.

You either have to dig for the information, or call the manufacturer directly. Even then you might not get an honest answer or any answer at all, and there's no sure way to tell without an expensive alloy analyzer.

If it seems like a really good deal, it's probably not the top-end stainless appropriate for an exhaust system.

That said, anything is better than the steel tubing typically used. THAT said, stainless doesn't flow any better than plain steel (for otherwise identical systems), so you could perhaps buy four steel systems to get the same lifespan and cost of one stainless system.

Also keep in mind anything after a cat is a personal aesthetic choice, the only critical performance areas are items like headers and turbo downtubes.

SteveRacer
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  • Austenitic stainless would be poor choices because of the risk of chloride stress corrosion cracking. The chloride would come from road deicing salts ( since tetra ethyl is no longer used). I actually had a 316 clamp on a muffler crack. – blacksmith37 Dec 02 '17 at 16:08
  • @blacksmith37 I don't doubt you. While there is some truth to what you say, and despite that I have training in heat treatment and metalurgy, I would suggest you take a look at what racing and piston aircraft exhaust is made out of. It's 300 series... therefore austentitic.I can't expain it, I only know what "is" is. If there's PH or martensitic stainless exhaust out there that's news to me. 321 seems to come as a favorite due to strength and resistance to fatigue over many extreme heat cycles. – SteveRacer Dec 03 '17 at 06:04
  • If it's a poor choice, it's the poor choice that's being made for decades by the "cost-no-object" racing and performance aircraft community. The only thing more exotic is inconel. – SteveRacer Dec 03 '17 at 06:04
  • Aircraft and racers see little road salt. And austenitics have a strength advantage at high temperatures like 900 F. Offhand I can't comment on weldability and thermal expansion , but I suspect there may be some "we always did this way" in the choice of austenitic exhausts. – blacksmith37 Dec 04 '17 at 20:25
  • @blacksmith37 While I agree, my original answer was tailored to what I perceived the OP's question was ... the giveaway was "aftermarket". While not impossible, I suspect that anyone capable of buying/fabricating an inconel or nimonic exhaust system probably would not be asking this kind of question here. – SteveRacer Dec 05 '17 at 04:48
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Nimonic is probably the best material with its high temperature and corrosion resistance - the price may not be what you want though :)

Solar Mike
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  • Just curious which aftermarket manufacturers actually use Nimonic for exhausts? I get it could be used as such and very successfully, but I'd bet only supercars would (or even could) get such treatment. I've not heard it used for aftermarket or production use for exhausts, so am really interested to find out where it can be purchased as such? How broad is the use? Can it be had for any make/brand? – Pᴀᴜʟsᴛᴇʀ2 Dec 02 '17 at 13:40
  • I have it by word of mouth that some fitters who used it in the aircraft industry as part of their job made bike exhausts "on the side" as it were... Been clamped down on though as well as the Titanium darts made from scrap as well... – Solar Mike Dec 02 '17 at 14:21
  • Inconels and Incoloys would be as good and much more available, you still won' want to pay for them. – blacksmith37 Dec 02 '17 at 16:03