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Exhaust Advice

Just an observation since I've been asked numerous times lately about my experience with the Sutton exhaust. I got one of the earlier ones so it didn't have as much heat. I can't really complain about that since they've made improvements there. I tweaked and modified a few things to make it better for my needs. And I used it for quite a few years. So i'm not going to bash their product.
The only thing I'm going to say, is get an exhaust that fits your needs. It no longer was serving it's purpose for me so I went to the Atlee hot rod muffler and it serves all my present needs.
I spent almost 8 hrs is Sub zero weather the other day much of it with the door open, and was never cold once.
But that isn't a need some of you have.


Sent from my E6810 using Tapatalk
 
I am unwilling to attach anything inside the shroud in any way other than welding by a competent shop. That includes wrapped springs, which are sometimes suggested. If any piece breaks loose from corrosion or vibration it could potentially go right into the engine.

Which is why Citabria and others install (or at least should) a metal filter screen at the outlet of their carb heat source regardless of what's inside the exchange unit.

Gary
 
I agree that internal baffling should help, however it should be welded to the muffler, not the shroud. The shroud needs to flex. Also, some sort of turbulence generators, such as Atlee Dodge uses on their hotrod muffler should help. I've already discussed doing this with my IA (certified plane). His opinion is minor alteration.

I am unwilling to attach anything inside the shroud in any way other than welding by a competent shop. That includes wrapped springs, which are sometimes suggested. If any piece breaks loose from corrosion or vibration it could potentially go right into the engine.
I disagree with welding the baffling to the muffler even with only an approved shop doing the welding. Welds on the muffler can are subject to extreme temperature changes and vibrations along with extensive expansion and contraction of the base muffler s/s. This is a characteristic of stainless steel when used in exhaust systems. With age, the surface of the can becomes warped and burned which would impart further stresses and the concentration of the warping along the baffle welds. This promotes cracking along the edge of the weld bead. Then you expose yourself to Co and less life from your expensive muffler. The Z baffle along the flat of the shroud is not subject to the destructive stresses which it would be if it were on the muffler. It is the muffler which flexes, not the shroud. There should be a little clearance between the Z baffle and the muffler. It is common to place this sort of baffle on the shroud. My 185 has this sort of Z​ baffle installed by Cessna. That shroud is now 43+ years old still in good shape.

Some mufflers have numerous studs attached to the can for heat dissipation. It is not uncommon to find radial cracks emanating from these studs in the can surface.
 
I guess I'm not picturing what you mean for a baffle welded to the shroud. The shroud has to bend a lot to be removed from the muffler. The essential shape of baffle I'm envisioning would prevent that.

The muffler is already welded, at the ends and at the bulkhead separating cabin and carb heat. The Atlee Dodge Hotrod muffler, which seems to have a good reputation for longevity, has numerous small vanes welded to the muffler can for heat transfer. I can envision a baffle of the correct material designed to add no more residual stress to the muffler can than the Atlee vanes. At least I think so - - -
 
The shroud is shaped like a tin can. One direction is round the other direction is a straight line. The Z stiffener goes along the straight direction. When you bend the shroud to remove it, the Z will not move or have any stresses placed upon it.

Yes the muffler is already welded. When mufflers fail it is generally but not always along the edge of a weld. Sometimes the crack forms along the bend in the end cap. You have no idea of where there may be internal stresses which were created in the muffler when it was made. Any alterations to the original may trigger a fault. Unless your muffler is new never used it will have some deterioration. Older used stainless exhaust components are more difficult to weld and more prone to cracking as a result.

These suggestions are only suggestions from what I have observed over the past half century of working on airplanes. Why risk premature failure of a muffler when a minor mod to a shroud will solve an issue? You can weld the baffle to the muffler if you wish. It may be successful or it may not. Your choice. If it were me I would prefer to make a new shroud than to buy a new muffler. I can do a shroud in house from locally purchased materials. A muffler $$$ to someone else.
 
For anyone still interested in this carb heat rise issue, I have gone to eBay and purchased a dual display digital thermometer. I also purchased a couple of thermocouples long enough to reach from the carb heat air inlet at the muffler shroud and the 2nd one at the carb heat flange at the carb heat box to the instrument velcroed to my panel. Just tucked them inside the scat tube under the clamp. $40 well spent
 
Is this the picture? And is that tiny tea cup the only collector for the heat? If so, it is no wonder you don't get any rpm drop.

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Distance? Look at my previously posted pictures. The distance is zilch. The hose to the carb heat box is directly adjacent to the air inlet. The air flow assumption is that it all sort of swirls around the #2 and 4 pipes and the end of the muffler can to absorb heat and then comes back to the hose to merrily flow to the carb heat box. I picture the air flow going to the carb heat box directly from the opening to the hose.
 
The FAA certified that exhaust.

After having a 2nd cup of coffee I understand that this is not the answer you seek and I really do not want to see this discussion deteriorate similarly to adding belts to a PA-12. Perhaps we could just answer the question that gets asked.

I have suggested a cheap way to take actual temperature measurements for any owner who has a concern. Some actual data instead of an opinion based upon not much. According to PM’s I have received carb temp probe temperatures seem to vary wildly from airplane to airplane. My opinion is that carb temp probe readings are at least partially a factor of how hot your oil pan, and the carburetor attached to it, is. So gather your own data is my advice, Jim.
 
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Jim,
You have been very fortunate that you have not encountered strong ice making conditions. All that collector does is to raise the already heated cylinder cooling air a little bit.
Just for the fun of it, connect the carb heat hose to the cabin heat outlet from the muffler and report back here.
 
Cruiser...have you run heat rise tests and if so is the info available? Also for the cabin heat output vs carb heat temps? Will be valuable to see if it meets certification.

The reason I asked who did the certification was that office may have prior data available for comparison with yours.

Edit: This appears to be the Office. Chicago Aircraft Certification Office (ACE-115C), Tel: (847) 294-7358

"Installation of modified Grumman AA-5B exhaust system assembly, P/N SUTN201 or P/N SUTN301. Only for those PA-18 series aircraft equipped with Lycoming O-320 or O-360 series engines, whether by original factory installation or by STC."

Gary
 

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Cabin heat vs carb heat is not a viable comparison on this system because literally 100% of the muffler can underneath the shroud provides cabin heat. Carb heat is taken off the end of the can and from around #2 and #4 exhaust risers as the air is sucked by on its way to the carb heat box. Piper dedicates half the muffler can each to carb and cabin. Not so with this system. I believe this has all been exhaustively discussed previously.
I posted a public comment by Steve’s aircraft that he tried 3 different muffler cans trying to meet the required temperature rise for an STC he owns. I find that very interesting.
Some members believe the carb temp probe provides some data as to whether they are getting adequate carb heat. I believe that to be debatable since PM’s indicate temperatures inconsistent from one airplane to the next.
My goal with resurrecting this post is to inform on the availability of a cheap digital thermometer that when used with a pair of thermocouples on both ends of the carb heat scat hose some interesting temperature data might be gained. Good or bad, at least I will know exactly what the air temperature is, Jim
 
Jim,
You have been very fortunate that you have not encountered strong ice making conditions. All that collector does is to raise the already heated cylinder cooling air a little bit.
Just for the fun of it, connect the carb heat hose to the cabin heat outlet from the muffler and report back here.
I did that, and was very surprised that it made little difference. A "few" degrees; few enough that I don't recall the actual number.
 
Cabin heat vs carb heat is not a viable comparison on this system because literally 100% of the muffler can underneath the shroud provides cabin heat. Carb heat is taken off the end of the can and from around #2 and #4 exhaust risers as the air is sucked by on its way to the carb heat box... Jim

It may be of some value if the temp rise of the cabin heat is puny and barely meets or exceeds the 90* rise from CAR 3. I don't know but if so (assuming it's puny) then how can the carb heat from a "teacup" fitting be expected to meet the requirements?

Gary
 
Ok, cabin heat is superb. I never open it more than half way. But that is a subjective observation that is not real helpful in regard to this discussion.
I don’t know how the carb heat from a “teacup” fitting is supposed to meet the requirements. The seller is absolutely adamant that it does. Apparently the FAA is satisfied that it does. I will have some temperature numbers shortly.
 
I will say this - - End of March I was scud-running (great vis, very low ceiling) in eastern Oregon and suspected some carb ice, so I pulled carb heat. The engine immediately stumbled a bit, then quickly the RPM went well up from where it had been.

I looked at the carb temp with the heat pulled and it was right close to 32 - not a comforting number. BUT - bottom line, the carb heat was definitely effective, carb temp readout notwithstanding. So either there is an inaccuracy in that temp measurement system, or something else I don't really understand is in play. Thing is though, it worked just fine with known carb ice. (see the little mod I did, post #107).
 
I do not believe this is correct. The cabin heat is taken off the entire muffler under the can via Ram air. The carb heat is taken of the end of the muffler, outside of the can, and off a small portion of the left hand exhaust stacks under the small shroud. No ram air. This is a view of the carb air intake. Now if a guy was creative, and non certified, I suppose a Y tube could be used in the cabin heat duct to provide fully muffler can heated ram air to both cabin and carburetor heat.

Cruiser, now that I have gotten into this part of the project I see that you are absolutely correct. Seems to be a need to preheat air going into the carb air pick up, (at the junction shown in your photograph in the proceeding post)
 
I do not believe this is correct. The cabin heat is taken off the entire muffler under the can via Ram air. The carb heat is taken of the end of the muffler, outside of the can, and off a small portion of the left hand exhaust stacks under the small shroud. No ram air. This is a view of the carb air intake. ----Now if a guy was creative, and non certified, I suppose a Y tube could be used in the cabin heat duct to provide fully muffler can heated ram air to both cabin and carburetor heat.[/QUOT


Has anyone tried using the whole muffler for more cabin heat and intalled a Y pipe so it could also be used for a more robust carb heat ?
 
I purchased an electronic thermometer that uses 2 type K thermocouples for the heat reference. eBay, less than $25. I Installed them at both ends of the carb heat scat hose, inside the hose. 6’ leads with the thermometer inside the airplane. In flight I get air temps at the heat box about 180 degrees above ambient. Dunno how that compares with any other exhaust system but I assume that is warm enough to melt any carb ice.
Having done that experiment I also sent my carb to Marvel Schebler for testing on their flow bench. Beyond worn out was the report back to me. Carb has been overhauled and flown for just a few hours. No carb ice type symptoms experienced
as of yet, Jim
 
I do not believe this is correct. The cabin heat is taken off the entire muffler under the can via Ram air. The carb heat is taken of the end of the muffler, outside of the can, and off a small portion of the left hand exhaust stacks under the small shroud. No ram air. This is a view of the carb air intake. ----Now if a guy was creative, and non certified, I suppose a Y tube could be used in the cabin heat duct to provide fully muffler can heated ram air to both cabin and carburetor heat.[/QUOT


Has anyone tried using the whole muffler for more cabin heat and intalled a Y pipe so it could also be used for a more robust carb heat ?

Dangerous. If the right conditions were set up, such as lower cabin air pressure compared to cowl air pressure, it could lead to most or all hot air going into the cabin vs into the carb.

Web
 
I wouldn't be happy with it unless it was linked to automatically shut off cabin heat when carb heat was selected.

Web
 
I do not believe this is correct. The cabin heat is taken off the entire muffler under the can via Ram air. The carb heat is taken of the end of the muffler, outside of the can, and off a small portion of the left hand exhaust stacks under the small shroud. No ram air. This is a view of the carb air intake. ----Now if a guy was creative, and non certified, I suppose a Y tube could be used in the cabin heat duct to provide fully muffler can heated ram air to both cabin and carburetor heat.[/QUOT


Has anyone tried using the whole muffler for more cabin heat and intalled a Y pipe so it could also be used for a more robust carb heat ?



i don’t think it would be wise to take the hot forced air from the cabin heat system and put it into the carb heat intake. The carb heat intake is not meant to be forced, it is brought into the system slowly and in limited volume by the vacuum from the engine through the carburetor. When looking at other systems such as the carbon cub, they restrict air intake to the carb heat air system by drawing it through limiting holes in the carb heat air intake system. Pre heating the vacuum drawn air to the carb heat system might be appropriate.
Stu
 
i don’t think it would be wise to take the hot forced air from the cabin heat system and put it into the carb heat intake. The carb heat intake is not meant to be forced, it is brought into the system slowly and in limited volume by the vacuum from the engine through the carburetor. When looking at other systems such as the carbon cub, they restrict air intake to the carb heat air system by drawing it through limiting holes in the carb heat air intake system. Pre heating the vacuum drawn air to the carb heat system might be appropriate.
Stu[/QUOTE

Web: I was envisioning a Y pipe with one outlet going to cabin heat and the other, which could be restricted, going to the carburetor. A flapper valve, at the Y, would direct flow. The valve would flow 100% to cabin unless carb heat was chosen.

Stu: I do see the potential for too much hot air going to the carb. A ring or plate with holes could restrict the flow to a 100 degree rise at average temperatures.

Thank you for your comments.

Jonny
 
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