STM Custom Aluminum Exhaust
13 Attachment(s)
STM recently prepared a custom aluminum exhaust for my RX-8.
Attachment 223670 Attachment 223670 Attachment 223672 Attachment 223673 Attachment 223674 Attachment 223675 Attachment 223676 Attachment 223677 Attachment 223678 Attachment 223679 Attachment 223680 Attachment 223681 Attachment 223682 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 fucking 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. |
Nice. Seems risky, but nice.
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Looks nice.
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Shiney! :) you should of tilted the muffler a little. Other then that cool.
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Originally Posted by cretinx
(Post 4547903)
If you're familiar with RX-8s, most exhaust setups sound like a robot fucking a sewing machine.
:spank: |
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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Originally Posted by 9krpmrx8
(Post 4547909)
Nice. Seems risky, but nice.
I'm a risk taker, a heart breaker. Or something else cliche. Whatever. I do what I want. You don't know me. |
Yep, hopefully it works well for you.
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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". |
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. |
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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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 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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Did you ask them if they build or have built exhausts for a rotary powered car?
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Should have used 6AL-4V Titanium. :naughty::naughty:
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1 Attachment(s)
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. Attachment 223559 |
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. |
gotta admit though ... for aluminum, those welds are quite sexy.
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This is awesome. I'd be interested to see how it holds up. Keep us updated
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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 . |
subbed for the long term (or short term) result .....
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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 . |
Bump for results. How did this exhaust hold up?
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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 |
:lol: I was just curious if the exhaust melted or not.
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The really funny part is that the first exhaust for the RX8 that I built back in 2005 using stainless steel along with an OE muffler pipe only weighed 9 lbs
https://www.rx8club.com/series-i-aft...e2/#post922293 |
Looks like the exhaust held up though.
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it doesn't say aluminum, so pure speculation until someone verifies it
however, I've seen plenty that didn't including the previous link to an RX8 specific failure ... If it never breaks you are good. If it breaks at the worse possible time you could be heavily inconvenienced or down-right screwed. If you think 3 lbs is worth aluminum over stainless steel for a cat back then more power to you. The problem in general is most people use too thick for SS (and/or wrong grade for the manifold/cat pipe) making it heavier than necessary. My entire SS exhaust system with manifold, cat, mufflers, & hangers is under 30 lbs total. The manifold was built in 2006 and is finally starting to give out despite being T321 material. The new manifold/header/whateveryouwannacallit that I hope to build soon will hopefully use Inconel 625 material for the primary tubes. That's the plan anyway. |
Originally Posted by Harlan
(Post 4663251)
Looks like the exhaust held up though.
Assumptions101: https://autophiliac.wordpress.com/20...exhaust-broke/ . |
Wow, I stand corrected.
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:lol:, well he was warned.
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