Aluminum or inconel downpipe?
08-27-12, 01:08 PM
#2
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.
08-27-12, 01:59 PM
#4
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.
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.
Last edited by RotaryEvolution; 08-27-12 at 02:04 PM.
08-27-12, 02:48 PM
#5
the implications matter
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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.
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.
08-27-12, 03:21 PM
#6
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^^^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.
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.
08-27-12, 05:57 PM
#7
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
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
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08-27-12, 09:31 PM
#9
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...
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...
08-27-12, 10:15 PM
#10
Original Gangster/Rotary!
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^^Exactly. If you want a $3000 downpipe, have at it 
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.
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.
08-27-12, 10:46 PM
#12
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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.
08-28-12, 10:39 PM
#15
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.
Stainless is the best choice, no reason to use anything else.
08-29-12, 09:01 AM
#17
Wastegate John
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^ 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.
08-29-12, 02:57 PM
#18
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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...
08-29-12, 08:39 PM
#22
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.
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.
08-29-12, 11:31 PM
#23
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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.
08-30-12, 02:56 AM
#24
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:
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)