STM Custom Aluminum Exhaust - RX8Club.com

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STM Custom Aluminum Exhaust

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Old 11-25-2013, 11:00 AM
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STM Custom Aluminum Exhaust

STM recently prepared a custom aluminum exhaust for my RX-8.

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The exhaust was built for SCCA Autocross "Stock" class competition. This means it can be replaced from the catalytic converter backwards, and must comply with a 95 db sound limit. It must exit the stock exhaust location.

We went from a dual to a single setup. They used thick wall aluminum with their welding expertise, retained the factory resonator and went with a single muffler. The header collector is 2.5" so the exhaust bottleneck is up there, and I wasn't going to see any power gains by going larger, so the piping is 2.5". Power is useless in autocross anyways.

As you can see, the weight savings are substantial.

The sound is wonderful and completely streetable/easy to live with. If you're familiar with RX-8s, most exhaust setups sound like a robot ******* a sewing machine. This is just a nice, rich somewhat exotic gurgle. Minor little pop-pops on throttle lift off.

STM was a pleasure to work with, and stand by their work.

I say this because several people have informed me that this setup is absolutely 100% going to fail, but so far its been great.
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Old 11-25-2013, 11:37 AM
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Nice. Seems risky, but nice.
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Old 11-25-2013, 12:07 PM
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Looks nice.
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Old 11-25-2013, 12:38 PM
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Shiney! you should of tilted the muffler a little. Other then that cool.
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Old 11-25-2013, 12:49 PM
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Originally Posted by cretinx View Post
If you're familiar with RX-8s, most exhaust setups sound like a robot ******* a sewing machine.
Raise your hand if you actually stopped here and took the time to try and picture this

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Old 11-25-2013, 12:53 PM
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Good deal! I bought a lot of parts from them when I was building my Evo and Galant. They are good shop. I know they do aluminum exhausts quite often.
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Old 11-25-2013, 01:46 PM
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Originally Posted by 9krpmrx8 View Post
Nice. Seems risky, but nice.
Nothing ventured, nothing gained.

I'm a risk taker, a heart breaker.

Or something else cliche.

Whatever. I do what I want. You don't know me.
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Old 11-25-2013, 02:31 PM
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Yep, hopefully it works well for you.
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Old 11-25-2013, 03:17 PM
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The melting point for aluminum is around 1200 degrees F. So, one would think it would melt under extreme situations. I would. So one will ponder the question, When? You're just doing Autocross with it so that's a blessing there. Not really enough time to get the exhaust temp sizzling. But I can not help but wonder how long before she burns through. I hope it doesn't of course. But.
Also how thick of tubing did they use? You mentioned it was "thick wall".
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Old 11-25-2013, 03:25 PM
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Yield Strength


Edit: That article gives information on the strength of aluminum compared to other metals over a temperature range. You can see from the fall off that aluminum exhaust is going to be extremely fragile when subjected to the exhaust heat, even if it doesn't actually melt, and heat cycling it will probably exacerbate the issue significantly.

6061-T6 aluminum however has great strength properties below 400F. The strength rapidly decreases and at 1100F, it has no strength as it is close to melting. In fact, it is interesting to note that at room temperature, 6061-T6 is stronger than the stainless alloys included.
...
CP-2 titanium has very good strength up to around 800F. It is not recommended for continuous use over 800F or intermittent use over 1000F.
It doesn't take much searching to find complaints about titanium exhausts cracking on RX-8s. Aluminum is going to be even worse.

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Old 11-25-2013, 03:26 PM
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With a stock cat that sees temps of 1600F+ during regular driving it seems to be a risky endeavor. But there is only one way to find out kudos to him for doing it. I would love a 6lb exhaust to impress everyone when I hard park.
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Old 11-25-2013, 03:31 PM
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TX

Originally Posted by RIWWP View Post
Good read, thanks.
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Old 11-25-2013, 05:13 PM
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Well, again, the company put their name on it so if it fails like most people think it will, then they're more than willing to back it up so I'm not worried about it failing.

That said, they have several of these setups on cars that run as hot or hotter than this one.

If you don't know who they are - home of the fastest GC Impreza in the world, fastest stock turbo Evo in the world, and pretty much everyone who works there daily drives a 9 or 10 second car.
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Old 11-25-2013, 05:31 PM
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That is cool, but they seem like they build piston powered drag strip cars. But if they back it then it's all good, hopefully it works out well.

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Old 11-25-2013, 05:56 PM
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Did you ask them if they build or have built exhausts for a rotary powered car?
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Old 11-25-2013, 11:01 PM
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Should have used 6AL-4V Titanium.
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Old 11-26-2013, 11:53 AM
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This is not what I would consider to be thick wall. What I would consider a "thick wall" would be at least 0.216" (Schedule 40) wall thickness. But still as mentioned, heat is a factor in the deterioration of the metal integrity itself. So even if you used a thicker tube, I feel the outcome would be the same. A disposable exhaust.

I'd like to see it hold up. And I hope it does. Losing 30 pounds is a good thing.


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Old 11-26-2013, 03:19 PM
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We'll see. I'll obviously report any failures.

FYI the cars that are running these for daily use are powered by 4G63s and are running EGTs in the 1400-1600 range. Typically 1400-1500 at cruise on the highway.

I talked to our local Grand Am race team who used to run RX-8s and they told me that they typically ran a 1600 EGT at the manifold during a race. Considering this car will never be run that hard, I'm not TOO worried. Of course, they also told me that this experiment was going to end in miserable failure.
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Old 11-26-2013, 07:14 PM
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gotta admit though ... for aluminum, those welds are quite sexy.
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Old 11-28-2013, 02:30 PM
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This is awesome. I'd be interested to see how it holds up. Keep us updated
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Old 11-28-2013, 04:13 PM
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It *will* break

Aluminum cannot take 1400F+ temps no matter what anyone claims, it has already been tried on the Rx8. You might get it to last with Sch 40 pipe, but then it weighs a lot

There's a reason I use T321 20 Ga

http://www.burnsstainless.com/yieldstrength.aspx


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Old 11-28-2013, 04:18 PM
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subbed for the long term (or short term) result .....
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Old 11-28-2013, 05:24 PM
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Eric's exhaust worked awesome with no signs of damage for the entire year except for a slight dent from a stray cone. Unfortunately, the fact that I don't have any heat-extracting turbocharging devices in my exhaust stream coupled with the fact that rotaries have pretty extreme exhaust temperatures to begin with meant that mine ended up cracking and falling off while autocrossing in Nebraska. That made for a long, loud drive home. I ended up reattaching the old Borla single-exit exhaust to use for the rest of the season.

ICEngineering: STX RX-8: 2012 Season Overview



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Old 02-09-2015, 03:30 PM
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Bump for results. How did this exhaust hold up?
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Old 02-09-2015, 06:12 PM
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^^noob ...

https://www.rx8club.com/rx-8s-sale-w...rx-8-a-256900/

They don't have anything for an RX8 listed on their website so it would appear to be custom only at a minimum
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