Aluminium Exhausts

So I thought aluminum would be a no go for any part of the exhaust but a bunch of people on a Facebook group said plenty of cars are running Aluminum exhausts after I commented on a dump pipe someone had made from aluminum saying it would not last..

I do not understand how?

It would have to be very well supported as at even mild temperatures ali loses its strength, Next to no bends and very free flowing. Even then id only think it would last on a drag car where it only needs to survive for less then 10 seconds at a time.

But some people said Nascar uses ali exhausts from which my quick googling could neither confirm or deny.

few people saying pistons and heads are made from aluminum duh... Uh yes but they are more then 1.6mm thick and are constantly cooled by the oil/coolant/fuel.

No one has been able to explain it other then "plenty of other cars do"

So just want to get to the facts so I can understand it myself, and possibly employ it... To think ive been making exhausts from heavy stainless all this time lol. But yeh im not convinced its a reality outside of a very narrow use and even then as a "consumable"

The ONLY instances I know of - and there may be plenty of cases where I'm unaware - is way back in the sixties and some of the factory-backed drag race cars running classes where tube extractors (headers) weren't legal. Some used exhaust manifolds cast in aluminium for weight savings and, even with the additional thermal mass and lower temperatures from being N/A, they only lasted a few runs.

About the closest I can say is many exhaust systems use what is called an 'aluminised coating' which is basically a thin coating of aluminum applied to prevent corrosion. You'll see it as a grey finish, and I suspect this is what the idiots others are thinking of?

There are some very effective heat barrier coatings, that may help reduce heat transfer from the gases to the metal, but I VERY much doubt they would be sufficient.

As you said, not only are there the thermal problems of them melting and losing strength, but there would be considerable stress from thermal expansion and aluminum has very poor fatigue resistance.

For the cold side, alunimum is a good choice, as there are much lower pressure and temperature levels to contend with and it's cheap, easily formed, and welded.

Oh, any chance they're thinking of TITANIUM? That offers considerable weight savings, tolerates very high temperatures, has the strength required, etc, and is commonly used where weight savings are at a premium and the higher costs aren't as important.

For those of us with real-world bank balances, stainless steels or inconel would be better choices.

Nope definately Aluminium... here is a link to the post, not sure if it will work?

https://www.facebook.com/groups/FabricationLife/permalink/626658481339670/

Pics attached... as you can see its a S bend with a 180 degree one way then a 90 degree out

Ah, he's doing it, but he hasn't tried it yet, nor have those I saw commenting.

I would be VERY surprised if it lasts for a run, even allowing for the drastic temperature drop across the turbine.

The melting point of pure aluminium is ~660C, and as other alloying elements are added, it only goes down and in some cases as low as ~550C. When you consider it's not uncommon to get EGTs of well over 1000C, that is a LOT to lose through the turbine assembly.

Of course, it isn't that simple, as there is normally a transition zone between the first, lower point where the alloy is partially melting - softening - and when it is completely melted at the 'melting point'. That initial temperature can be a lot lower than the actual 'melting' point - this figure (if it works) is in Russian - https://aluminium-guide.com/wp-content/uploads/2014/01/temperatury-likvidus-solidus-alyuminiya.gif - but the last two columns have the point where the alloy first starts weakening and the point where it's completely melted. It's over 25 years since i studied metalurgy, so if you're interested I'd suggest reading the whole article - it's in english - https://aluminium-guide.com/en/temperatura-plavleniya-alyuminiya-i-alyuminievyx-splavov/

I haven't been able to find - you may - the actual exit temperatures from the turbine, but you can get a good idea by comparing this chart - https://www.pinterest.nz/pin/472103973420445161/?nic_v2=1a7LWUyND - to the colour of the exhaust you see on dyno' runs, for example - https://www.youtube.com/watch?v=c2eWHNSaSZU - NOTE, headphone warning! Also, bear in mind the inside will be slightly hotter as it's receiving, not rejecting, the heat energy.

This has always interested me too, most of the cars I have seen running alloy exhausts use Methanol with a cooler burn than regular fuels. Thanks for all the input guys.