Aluminum or inconel downpipe?
 

I wanted to know if anyone has used aluminum or inconel
or maybe titianium for there downpipe. If so what are your experience
with them. If you have pics can you post them. Thanks Justin

Good question, good thread. Not trying to thread jack but no reason to make another thread. If someone has a aluminum Down pipe as well as having there whole exhaust system please elaborate. Ive been scouting, looking for someone with an aluminum downpipe/exhaust to get an idea on sound, durability, opinion ect.

I'm thinking Enzo did one out of aluminum.

i can just picture an exhaust rolling under a car as soon as it gets speed bump checked.

if you're going to attempt it i would suggest mid car(catback) you use the aluminum versus turboback, the heat will dissipate dramatically by that point. to join the steel and aluminum use a slipper clamp.

Inconel would be much better to use than aluminum but it's going to be tough to find a shop to work with it.

You're comparing one of best materials for high heat applications (inconel) with one of the worst (aluminum).

My 0.02: aluminum doesn't belong in exhaust systems at all. Aluminum REALLY doesn't belong in a rotary exhaust system which run hotter than their piston counterparts. I only know one guy who tried it. It failed in less than 40 minutes of run time at the track (sagged and split just beyond a weld seam). Now maybe you could optimize the geometry to have less of a hot spot but you're still not talking about a system that will have longevity measured in years. There are almost infinite ways to save weight would perform better.

Here's a few tech articles from Burns Stainless, that'll help you.

Yield Strength (AKA Can I use aluminum in my exhaust?)
Burns Stainless LLC - Inconel

321 ss is an intermediary choices for stainless, it'll hold up better than 304 at the same thickness. Few guys can afford titanium and those than can (F1, NASCAR) won't run it except aft of headers. That should tell you something.

^^^Good stuff

The exhaust inserts in the rotor housing are made of inconel, as are the valves in many wastgates. If you can aford it, inconel would be pretty slick...

I think Alumium melts at 1,250 degrees. My exhaust temp are 900 to 1000 at idle and 1800-1900 at full boost, couldn't see aluminun lasting too long.

ok so it looks like inconel is the way to go. I know and heard that the f1 guys use it for headers.
I was at seven stock a few years ago and saw the 4 rotor rx8 drift cars and they said the exhaust was made of inconel. i guess thats why i am asking to see if anyone has done it here on the forum.
keep the posts coming. and if anyone got pics please post

There was a few FD threads that had aluminum exhausts after the DP. Dunno whatever became of them. For racing applications aluminum would be pointless. For a cruiser street car i think it wouldnt be to bad after the down pipe.

The melting point of aluminum is 1220F. Turbo rotary exhaust is what... 1625ish degrees?
NA is even hotter I've read. Just cruising around I'm sure is less, but probably still above 1220F... Why would people even try to use aluminum?

I can't imagine how costly inconel is...

^^Exactly. If you want a $3000 downpipe, have at it :D

I lucked out and found a full Titanium 3.25" resonated midpipe and 3.5" catback from R-Magic in Japan..... IIRC each piece is about 8 pounds.

inconel actually isn't severely expensive, machining and working it is.

that shit is harder than titanium i swear.

I built an aluminum catback for my car, it split at the weld. For a street car I think it would work fine. If you can find some inconel go that route, I just finished an inconel turbo manifold.

The guy that had a nova rotary has a 4inch aluminum downpipe on his(can't remember his exact name).

86v8rx7 can u post pics of the manifold. And let us know the good and bad after it is installed and run for a while. Thanks

Stainless will be the easiest route. Aluminum will fail quickly, and is not worth the trouble. Titanium requires time and skill, also not worth the trouble. Inconel is difficult to work with because it work hardens quickly and will destroy machine blades. It works well to save weight in applications where a few lbs makes a difference, but is not cost effective by any means.

Stainless is the best choice, no reason to use anything else.

Hey scorpionT isn't the inconel also good for heat and not just weight?

^ Yes, inconel is excellent for heat, however the downpipe does not get hot enough for you to benefit from using inconel over stainless. You can use a thinner gauge with inconel though so you would be able to save weight using it.

Have to agree, ALum woud fail faster, Inconel wouldnt benefit you for the price. if you wanted something super robust, do it outa 316 SS and then get that white lightning coating...

Precisely. Inconel is primarily used in applications that measure weight savings in grams rather than lbs. 321 and even 316 or 304 stainless will work just fine on your car.

Thanks for your input guys

I wonder how much more inconel would be then SS in making a 20b turbo manifold. This thread got me wondering. The welding is the same as far as I understand it.

thewird

I find it incredible that he doesn't seem to be a troll. Please don't use aluminum above 350 F folks, it gets soft like lead. Not good for any EGT, probably not even the mufflers. Just to cut off the question engine blocks are roughly the same temp as the coolant not the combustion gasses due to the dramatic difference in heat transfer rates.

IIRC inconel is too expensive for anyone who isn't doing a high end professional application.

Some googling revealed that a rare few try out aluminum downipes with double wall thickness. Some of them have even survived "so far" (months) and haven't blown like the rest. Dam, people will do anything. I don't think any sane big name manufacturer does this.

There is nothing wrong with using aluminum in a street or drag race application. That being said if anyone wants and inconel turbo manifold I have decent about of 1.875 .049 wall inconel 625 to build manifolds with.

titanium isent hard its actually realitivly soft. a good steel will be twice as hard as titanium.

and thats the reason why high end titanium lock bar folding knives have a stainless steel insert on the end that engages the tang. like this:
http://s4ecbdf58c5d19.img.gostorego....1_b_grigio.jpg
because they wear quickly and under high pressure/shock you can deform titanium causing loose lockup.

anyways what im saying is what titanium has for itself is its light weight and toughness(wont shatter), and of course a high heat resistance. though it dose not get very hard. (not that hardness would be any use in a exhaust system)

I tried googling for the price of 4" inconel but came up with nothing.
Does anyone have any idea? Not guessing, but has seen it on a website or talked a shop who sells it

Call Woolf aircraft they might have some surplus 4" you can get for a reasonable price, talk to Gary.

I believe turblown makes inconel heat shields. You could try contacting them to see where they get material from. Or you could call your local formula 1 team and see who they bought from ;)

There is nothing wrong with using aluminum in a street or drag race application. That being said if anyone wants and inconel turbo manifold I have decent about of 1.875 .049 wall inconel 625 to build manifolds with.

Except when you push it aluminum does crack. A crack greatly increases the chance of a fire if you do have an fluid leak onto it.

I know it sounds like if if if, but when you are seriously pushing your car this apparent "perfect storm" of circumstances happens much more than you would expect.

Just something as common as continuous 4th gear pulls tuning a car can easily cause this scenario.

Did you google inconel 625. It comes up with TONS of metal suppliers that have 4" tubing. All you have to do is call.

Have fun cutting it. Inconel that is

Yield strength of aluminum, SS and titanium vs. temperature:
http://www.burnsstainless.com/images...Strength-1.gif
http://www.burnsstainless.com/yieldstrength.aspx (link also has another handy image with strength to weight)

You can make your exhaust out of silly putty if that floats your boat and maybe even get it to work for a little while. But hot aluminum doesn't even make sense from a strength to weight standpoint. It would make more sense to lighten your exhaust by getting stainless tubing that is dangerously thin. Heck at least that would be stronger.

All metals soften at higher temperature but those with higher melting points soften slower. You can't assume it's good just because it's below melting; it shouldn't even be close.

Ah, that chart helps me understand something.

On a run at auto-x when I had dual drivers on a higher speed course I hit a cone with the muffler tip and it put a giant flat spot on the Ti tip like it was made of aluminum.

I pounded on it for hours with a ball peen hammer trying to get it round and finally put a torch on it which really seemed to help.

Now I see on that chart how weak Ti is with heat- it literally was as soft as aluminum when I smacked that cone.

These were made from 4" OD, 0.035" wall 321 stainless tubing. Stands up to the heat, and light as a feather...

http://www.flickr.com/photos/74953263@N07/6799374693/http://www.flickr.com/photos/74953263@N07/6799374693/ by http://www.flickr.com/people/74953263@N07/, on Flickr

http://www.flickr.com/photos/74953263@N07/7025378369/http://www.flickr.com/photos/74953263@N07/7025378369/ by http://www.flickr.com/people/74953263@N07/, on Flickr

http://www.flickr.com/photos/74953263@N07/6879294066/http://www.flickr.com/photos/74953263@N07/6879294066/ by http://www.flickr.com/people/74953263@N07/, on Flickr

what's with the snail shell cuts? i have seen it before but the real question is why? seems to make a 45 minute job turn into a 3 hour one.

Rather spend $ on something else besides pricey 4" mandrel bends maybe?

I've been running 4" aluminum exhast for a while with no problems. Just inspected it the other day and still no cracks. That said......I don't drive the car all that much and I used fairly thick aluminum tubing (3mm). The downpipe is ss though. No way the downpipe would last if it was aluminum. Too hot at the first bend. If it is a daily driven street car, I'd go thin wall 316 SS. With aluminum, I'd be worried about going through a puddle after the pipe has heated up. It'd crack out for sure.

And what makes you think that a simple mandrel bend is cheaper than many lazer cut pie pieces that are back-purge welded together:lol:? There are TONS of man hours in that downpipe, a skilled welder's labor is not cheap.

I would run aluminum any day of the week

Yes, but the is making something for himself- not a commercial product.

The rod, argon and pipe is cheaper than 4" mandrel bends and he obviously enjoys the welding...

And who says it wasn't a commercial product? He sells it too lol.

thewird

You are forgetting about the laser cut pie pieces of pipe.

Didn't meant to hijack the thread by any means, just offering it up as an alternative to using aluminum. Lighter in most cases and will hold up to any heat.
The pie-cuts are used for two reasons.... some people love the way it looks and simply want it. The other is that it makes puting together odd or complex bends very easy. When every piece is a known degree, there isn't any cutting, checking and re-cutting. Most of the time we'll also laser-etch a reference mark at 0 and 180 so we're able to roate them a known degree when snaking through a tight spot.

Aluminum: bad idea with heat.
Pie cuts: bad idea for flow.

See the last paragraph here:
Burns Stainless LLC - Welding Article Part 2