Thanks in advance for reading this question. I have a custom 13b engine installation where space is a premium (aircraft install). I am fabricating my exhaust tubing out of 16ga, 321 stainless for durability and weight savings. Since I have so little space I wanted to include a removable exhaust baffle inside the tubing and fully surrounded by the exhaust stream / pulses to attenuate the engine’s ear bleed causing sound. I’ll have a small 321 stainless spintech muffler at the end of the exhaust sequence to add to the sound attenuation effect. I was wondering, if I build my INTERNAL exhaust baffle out of 16ga, 321 stainless and have the OUTSIDE of the baffle sprayed with JetHot 2500, will the baffle survive the RX-7 intense exhaust gas environment since it will be surrounded on all sides by the intensely hot exhaust gasses? I am attaching a PDF of my baffle to this message so you can see my thoughts. Thanks in advance for your reply.

-J

 

the question is for how long. hard to say really, 321 is good, the coating is good, if you limit EGT's it should be fine. i put an EGT in place of the O2 sensor on my stock S5, and only saw 820C, which isn't much hotter than a piston engine...

 

my egts with 321ss was between 900-1000C +.. didnt have an issue but j9fd3s asked the right question.. For how long ...

 

If you are going to jacket the exhaust you can add a small NACA duct to the forward cowling and a piece of flexible scat duct to a spigot close to the engine. On the other end add another spigot and use it for cabin heat. All you have to do is attach it to a bypass valve so when the cabin heat is not needed it dumps the heated air inside the cowling. I would eliminate the need for coating, increase the life of the exhaust, and provide cabin heat. You could do a clamshell design so that you could disassemble it for inspection of the exhaust.

 

Thanks for the quick replies. So if I hear you all correctly I should see EGTs in the exhaust stream anywhere between 1472f and 1832f (using the Celsius to Fahrenheit conversion calc of (1.8*c) + 32 ). To that end I see that 1832f at the top end will surely heat precipitate the material over time and erode it away (which sux). This implies that if I *DO* fab this part out of 321 I will, over time, fab the part more than once (which also sux). Insofar as how long do I want the part to last ….. I only want to fab this baby once so forever is my answer …. Or at least longer than my time. These thought imply that for my “in stream” exhaust baffles I need to fab the part(s) out of Inconel 625 and call it a day. This is because purchasing 321 twice is about as expensive as purchasing Inconel 625 once. On the subject of cabin heat …. I plan to take advantage of the heat in the glycol via a heater core and TOTALLY avoid the specter of CO in the cabin. Again, many thanks for your input(s).

James

 

YEA!!!! I just got my 321 stainless 2-into-1 collector finished (Yes ... I know ... that RB flange is 304 .... but who's counting???). Here's where you can see some pictures. The baffle you see in Collector5 is 16ga 321. I think this baffle *might* not survive its environment :-\. No worries though .... I plan to put in an Inconel baffle downstream. Here're the pics->

http://www.tripleaser.com/images/Collector1.jpg
http://www.tripleaser.com/images/Collector2.jpg
http://www.tripleaser.com/images/Collector3.jpg
http://www.tripleaser.com/images/Collector4.jpg
http://www.tripleaser.com/images/Collector5.jpg

 

can't view the pics, under your personal account.

wanted to see where you got the inconel 625 from for the manifold and see how well it held up but i guess not. :P

 

Karack .... those images are direct URLs to an images dir on an external web server. You should be able to just type the URL in a browser and see the images. For instance, typing http://www.tripleaser.com/images/Collector1.jpg in your browser's URL line should show you the first picture of my 321 2-into-1 merge collector (at least it did for me). On the Inconel thing ... I'm still searching. That stuff seems hard to find.

 

"Forbidden

You don't have permission to access /images/Collector1.jpg on this server."

was just an FYI, maybe my computer just doesn't like that one server..

 

http://stores.ebay.com/Performance-P...=p4634.c0.m322

 

thanks 13B-RX3, for some reason i didn't think to check ebay... lol

all the sites i looked at were "call for pricing" which annoys the **** out of me. too bad they only list it up to 2 1/2 on that page, works for manifolds and wastegates but not for downpipes.

 

3.5" is the biggest these guys have.

http://woolfaircraft.thomasnet.com/r...d=&backtoname=

 

Double post

 

cool

now, do we know anyone who has used this for a rotary turbo manifold yet? curious how well it holds weight.

kind of sucks seeing all the manifolds in stainless, will eventually stress crack and they are heavy. granted it looks like it would be a pain to machine the flanges and the materials about twice as expensive.

 

If you can afford it and can find someone who can weld it good (this may be a problem) it is superior to 321 in every way.

http://www.skydynamics.com/Information/stainless.htm

I did a lot of research when i built my header. I ended up with 2 1/8 OD 2" ID 321 stainless. I have never had any issues with it at all. It is holding a 50# turbo with no bracing BTW.

 

don't get me wrong, stainless does the job for a good long while but onward and upward is a good thing. if inconel weighs half as much and outlasts stainless i figure it will be the next aim for most people.

 

All,

Here’re some pics of the manifold on my desk AND on my aircraft. It's a 2.7MG PDF linked to an external site (cause I can't upload 2.7MD here). Thoughts / concerns are welcome. Oh yea ... on the subject of finding someone to weld exotic / high temp nickle alloys (321, Inconel, Hastelloy, etc) ... the guy you want to call is named Eddie Wilbanks in Eads, TN. He did the finish work on my manifold and even did his best to clean up my jack-legged tacks that blew through (woopsie). His number is 901-359-8670. Enjoy.

http://tripleaser.com/CollectorPics.pdf

-J

 

No offense but those welds do not look good from what i can see. Did he back purge when he welded them? Also, i think a true collector would be much better. Simply welding the two pipes together and welding along the crotch is just asking for a crack. Welding the tubing to the face of the exhaust flange is also a big no no. I don't want you to think i am picking it apart, i have quite a bit of experience in aircraft exhaust and have seen just about any failure you could imagine.

 

13B-RX3 ... Yup ... not only back purged but done so in a sealed media blast cabinet that was evacuated / purged for 3 minutes to insure a complete lack of O2 in the atmosphere. In regards to the cracking at the merged tubes issue ... I thought that might be a problem but then I took a close look a number of turbo manifolds it seemed the tubing merged together and then immediately was welded to a flange With a weld across the crotch of the tube weld. In my case the tubing merges together, slips into a flare entry that serves as the beginning of an internal baffle and that then serves as the weld point for the ball joint. The ball joint serves as shock isolation from the airframe's vibration for the header and its’ welds and visa-versa. At the exhaust flange the tubes are slipped into the cups of the RB flange, seam welded on the outside (as you can see), and are as well welded inside of the flange where the tubing touches the inside of the cup (which you cannot see …. Woopsie). As such the tubes are NOT simply welded to the face of the flange (which would be truly foolish as you’ve indicated). Now that you have additional info, please share your thoughts on impending failure cases so I can further inspect / modify said header design to account for such short comings. Oh yea …. Thanks for the input; it’s this type of feedback that makes engineering fun.

 

One more thing on the welds .... upon inspection of the back sides of the welds there is clear penetration but 0 "sugar". The absence of “stainless sugar” motivated me to believe there was a distinct lack of high rate puddle oxidation *BUT* a good presence for weld site penetration. Is there another way I could check for weld site misbehavior?

 

I ran 18 Ga. T321 stubs at the manifold flange with 20 Ga. T321 all the way out on my NA Renesis/RX8 without issue. 16 Ga. thickness with 347 filler wire and a good argon back-purge should be plenty strong and durable, but the weld/fabrication quality and overall design play a lot into the end result. You could do a 22 Ga header with 625 Inconel for a NA motor. Burns Stainless was promoting it before the economy went sour 5 years ago.

A noted pro engine builder told me that coating light gauge tubing/manifolds would promote cracking. I didn't believe it then, but over time I've seen more coated stuff crack than non-coated, so none of my stuff is coated or wrapped anymore. I use stand-off shields/blankets and directed air flow instead. I'm sure somebody will disagree ...

IMO that resonator design will have more issues with the peripheral exhaust pulse vibrations than the heat. You may want to speak with Gary @ Coast Fabrication. They had to reconfigure their muffler for use on the 20B Grand Am cars to address this kind of stuff. I think he can probably come up with something better for you than the resonator/Spintech setup.

 

TeamRX8 … thanks for the input. I probably should have mentioned there’s’ an Inconel inline baffle in the mix here. The section of tube that is downstream from the ball joint slips over the lower ball joint tubing and form a mechanical fit for said baffle. I sourced my Inconel from Burns stainless and they are swedging both ends for me. Once I get the swedged tube one end will fit snugly inside of the 16ga, 2.5” OD down tube and the other will mate exactly to the 2.5” ball joint tube and the slip over will hold it all together on the top end. On the bottom end the 48 degree, 4” CLR bend will hold the bottom of the baffle in place. Said baffle will be MUCHO perforated with M5 holes in an effort to BOTH reduce the ear bleed inducing exhaust note *AND* avoid slowing the exhaust flow. THE PDF at http://tripleaser.com/BaffleInfo.pdf shows the inline baffle and the down tube. It’s at the end of all this that a Spintech Sportsman gets attached. Keep in mind, my space options are limited so I have to make some non-optimal decisions if I want to keep my hearing and keep my neighbors from arriving at my house with pitch forks …. Unfortunately.

 

Sounds like you have done a fair bit of research. The only other thing i could think of that could possibly help is a slip joint in one of the runners to allow for thermal expansion of the engine flange and tubing. Another thing you might look into is adding the N/A exhaust sleeves into your rotor housings to reduce the noise further.

 

13B-RX3 .... Yea ... I thought about doing a slip joint on one of the primaries near the RB flange. The things that made me feel OK about not doing it was the multiple flange welds, less than 1/32 spacing fit at the tube merge and slip over of the start of the first exhause baffle prior to the part where the ball joint attaches. Do you think I'll still have a diff heat expansion issues or do you think these things might allow me to dodge a bullet?

-J

 

All is progressing quite well now for this exhaust layout. I've decided to use Inconel 625 as the material for the in-line exhaust baffle. On that note, I just got a call from the machine shop where I'm having my baffle perforated and they said that Inconel 625 is, in fact, DAMN HARD. As such, if you'd like to smack yourself in the forehead with something DAMN HARD .... use a length of Inconel 625 tubing.

-J