STM Custom Aluminum Exhaust
11-25-2013, 10:00 AM
#1
STM Custom Aluminum Exhaust
STM recently prepared a custom aluminum exhaust for my RX-8.
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.
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.
11-25-2013, 12:46 PM
#7
11-25-2013, 02:17 PM
#9
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".
Also how thick of tubing did they use? You mentioned it was "thick wall".
11-25-2013, 02:25 PM
#10
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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.
It doesn't take much searching to find complaints about titanium exhausts cracking on RX-8s. Aluminum is going to be even worse.
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.
...
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.
Last edited by RIWWP; 11-25-2013 at 02:41 PM.
11-25-2013, 02:26 PM
#11
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iTrader: (46)
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.
kudos to him for doing it. I would love a 6lb exhaust to impress everyone when I hard park.
11-25-2013, 04:13 PM
#13
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.
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.
11-25-2013, 04:31 PM
#14
SARX Legend
iTrader: (46)
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.
Last edited by 9krpmrx8; 11-25-2013 at 04:57 PM.
11-26-2013, 10:53 AM
#17
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.
I'd like to see it hold up. And I hope it does. Losing 30 pounds is a good thing.
11-26-2013, 02:19 PM
#18
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.
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.
11-28-2013, 03:13 PM
#21
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
.
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
.
Last edited by TeamRX8; 11-28-2013 at 03:29 PM.
11-28-2013, 04:24 PM
#23
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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02-09-2015, 05:12 PM
#25
^^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
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