Size would be 4" maybe some smaller sizes if it proves a somewhat reliable exhaust. I'm not looking at reliability but, say it was for a class requiring full exhaust and the car gets driven on the street. I'm not aware if the aluminum would hold up for a street car or if I'd be better to use it as a track only exhaust. Anyway, here is what I am thinking of making it out of...two choices

4" 16 gauge 6063
or
4" 11 gauge 6063

Opinions on this....I got to go for now...lol

 

There is a reason aluminum isn't used in exhausts.

1) Aluminum has no fatigue limit. That means that with cyclic stresses, it will fail eventually, and there is no telling how long it will take. (Well, you could calculate it, but it is tough to do)

2) Aluminum creeps (deforms with very little stress) at a temperature lower than exhaust temperature. Aluminum melts only slightly higher than a "bad" EGT, so it is also possible to melt it directly.

3) Aluminum is highly succeptable to localized stress concentrations, and tends to crack instead of give like steel would.

So what it comes down to is how long do you need it to last? An aluminum exhaust will not last long. Even if you just used it after the downpipe, it would still develop cracks very quickly. It might be okay for a track car for a season, but you never know. If you cannot make absolutely perfect welds, I wouldn't even attempt it. I would recommend going with 20ga steel first.

 

With that siad...
I have 4" 6063 aluminum exhaust for over a year. it is 14 gauge and I purged welded it then heat cycled it. No problems so far. There's some pics on our site for interest.
I will make a post if it fails.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by beepy &raquo;</TD></TR><TR><TD CLASS="quote">There is a reason aluminum isn't used in exhausts.

1) Aluminum has no fatigue limit. That means that with cyclic stresses, it will fail eventually, and there is no telling how long it will take. (Well, you could calculate it, but it is tough to do)

2) Aluminum creeps (deforms with very little stress) at a temperature lower than exhaust temperature. Aluminum melts only slightly higher than a "bad" EGT, so it is also possible to melt it directly.

3) Aluminum is highly succeptable to localized stress concentrations, and tends to crack instead of give like steel would.

So what it comes down to is how long do you need it to last? An aluminum exhaust will not last long. Even if you just used it after the downpipe, it would still develop cracks very quickly. It might be okay for a track car for a season, but you never know. If you cannot make absolutely perfect welds, I wouldn't even attempt it. I would recommend going with 20ga steel first.</TD></TR></TABLE>

And that's why blocks and cylinder heads are made out of aluminum.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by backpurge &raquo;</TD></TR><TR><TD CLASS="quote">And that's why blocks and cylinder heads are made out of aluminum. </TD></TR></TABLE>
Blocks and heads are liquid-cooled so they never reach those temperatures. In addition, the hot exhaust gasses are very quickly evacuated from the cylinders. This isn't really a valid comparison.

 

why not just get it jethot coated or something?

 

Ok, I'm getting mixed opinions on this. CRVRX - I checked out your site. You've had non of these problems that are being described by beepy?

backpurge has a point but dwolsten doesn't think it is compareable. hmmm...

They make connecting rods out of aluminum, blocks, heads etc...

CRVRX - The weight is amazing that you have on your site. 6 lb 4" exhaust compared to 22 lb stainless 3"

More facts needed....like melting point of 11 gauge 6063 aluminum. I was talking exhaust from downpipe back.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 80884 &raquo;</TD></TR><TR><TD CLASS="quote">

More facts needed....like melting point of 11 gauge 6063 aluminum. I was talking exhaust from downpipe back. </TD></TR></TABLE>

6063 Aluminum has a melting point of 1150*F.

 

Bump! I'm doing some research on this right now. I don't see a problem with it as long as the aluminum is placed far enough from the trubo and motor. If the tubing is properly braced it will see very little stress from bending and twisting. It seems to be that the starting point would be key. What are exhaust temps like at say the fire wall? You may also want to check out burns stainless for good information on aluminum grades, though they say not to use al for exhast. You can also check out matweb.com for material properties if you are interested.


Modified by troyk kms at 8:24 AM 3/28/2006

 

PM Geoff from full-race or turbojesse they are both running 4 in alum exhaust.

 

I've never seen 11 gauge aluminum bends. 16 gauge is probably your only option if you want to go with 4" aluminum tubing.

 

4" 11 ga. 90* elbows aluminum
4" 11 ga. 45*
4" 11 ga. aluminum tubing

I can get the 11 ga no problem. But I can get 16 ga alot cheaper. But if the 11 ga would last twice as long as the 16 ga than the 11 ga is better. If the 11 ga lasts no longer than 16 ga there is no point in running the 11 ga.

4" aluminum comes in many different thicknesses

 

If you're going to go so thick, then what's the point in using aluminum? 11ga. al. can't be much lighter than 18-20ga. stainless.

 

I'm not sure on the weights of the different pieces I am thinking of using so your right tony, I may be defeating the purpose by going with thicker pipe. It just seams like it's hard to get good info on this because two people say different things.

Anyone know where I can find a weight comparison for different tubing?

I may end up just doing the 16 ga aluminum, it's cheaper and I could make two kits if one were to fail.

Tony, what do you think about the durability of the aluminum exhaust, not a daily driver but does get street driven. Geoff has said he has dented his exhaust from a pot hole before so to me if it didn't break when that happened than it has to be pretty strong?

 

buy your aluminum from Casey at Burns Stainless...... and along with the aluminum comes some great information on how to build the exhaust to last

i'll be using 4inch, 16g Aluminum for my exhaust this year

 

I've seen Geoff's exhaust, it's beat to hell, and still in 1 piece. If done properly (welded, supported, etc) i don't think you'll see any issues for a while. Eventually it'll fatigue and crack. I'm building a 3" aluminum exhaust with a burns muffler for an NHRA street stock car as we speak...

 

just liquid cool the aluminum exhaust duh....

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by beepy &raquo;</TD></TR><TR><TD CLASS="quote">There is a reason aluminum isn't used in exhausts.

1) Aluminum has no fatigue limit. That means that with cyclic stresses, it will fail eventually, and there is no telling how long it will take. (Well, you could calculate it, but it is tough to do)

2) Aluminum creeps (deforms with very little stress) at a temperature lower than exhaust temperature. Aluminum melts only slightly higher than a "bad" EGT, so it is also possible to melt it directly.

3) Aluminum is highly succeptable to localized stress concentrations, and tends to crack instead of give like steel would.

So what it comes down to is how long do you need it to last? An aluminum exhaust will not last long. Even if you just used it after the downpipe, it would still develop cracks very quickly. It might be okay for a track car for a season, but you never know. If you cannot make absolutely perfect welds, I wouldn't even attempt it. I would recommend going with 20ga steel first.</TD></TR></TABLE>

wise man... I agree.

Alluminum exaust=alluminum can. good for one use.

Make one out of Inconel like the f1 guys do

 

well, I take that back.

But alluminum isn't used in exausts for some reason....thats why they use titanium.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by drewbie &raquo;</TD></TR><TR><TD CLASS="quote">wise man... I agree.

Alluminum exaust=alluminum can. good for one use.

Make one out of Inconel like the f1 guys do </TD></TR></TABLE>

I guess I need to start making inconel blocks, rods, pistons, turbo compressor housings etc huh?

Seriously tho, a can is like probably like 50 gauge aluminum.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by drewbie &raquo;</TD></TR><TR><TD CLASS="quote">
But alluminum isn't used in exausts for some reason....thats why they use titanium. </TD></TR></TABLE>

Probably because they want the exhaust to outlast the car. As long as I get one year of racing + street use I would be happy.

I'm getting some good info from this thread. Thanks to all that have offered up info or advice...or even common sence
It looks to me like it will be made from 16 ga 6063 aluminum 4" and maybe even bigger! ha ha j/k

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by backpurge &raquo;</TD></TR><TR><TD CLASS="quote">
And that's why blocks and cylinder heads are made out of aluminum.
Wow bro. Doesnt it seems as if the exhaust gas exits through the same way? I mean, exit quickly yes, but what is it connected to? an exhaust. Doesnt it exit quickly too? Since heat do thin out as further it goes out. Ok, say, Aluminum Pistons? Those take then beating. Or Say, the block at the exhaust flange, Im sure thats furthest away from liquid, I beleive that area gets damn hot way over 1000d. (I will check with a digi thermometer soon) Or even a RED GLOWING manifold is bolted to the aluminum head, is that not HUGE heat factor? Didnt melt either?
But yea. I can be wrong again.

Im thinking about doing a 3" aluminum exhaust soon enough also, I will keep this thread updated.

 

Kick *** man! I'm debating on testing 3" alum on my sti to see how much of a beating it can take. I have like 3 exhausts for it already so if it fails I will just put something else on.

Definatly keep it updated with good info and anyone else can do the same

 

alluminum is also used in engines because of its expansion and contraction characterisitcs. It is also a softer metal so it was flex more. I guess this is why iron heads arnt safe to rev past a certain RPM because of vibrations.

i forgot to put a after my inconel post

 

Some aluminums won't expand more. You have to look at the percent elongations of a material. Also remember that blocks and heads are made from different alloys than is being talked about with this exhaust. The alloys exhibit different qualities under different conditions. Check out matweb.com if you're interested in the material properties.

 

i did some calculations for ya in regards to everyones comments (SS vs. Al)

1. One inch of SS 18 gauge 4in. tube wieghs 0.174 lbs
2. One inch of Al 11 guage tube weighs 0.144 lbs

so there would be wieght savings even with the heavier 11g Al tubing. Also i did not bother to calculate the 20 g SS becuase .035 wall thickness imo is to far thin for a street exhuast. hope this helps