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Exhaust Advice

At what OAT temp do you not get enough carb heat?

Im in the process of building the plane and getting ready to hang the engine. I don’t know that it will be lacking carb heat, I’ve just heard roumors and anticipating how to make the system as efficient as possible.
 
I have the Sutton exhaust and maintain quite a few Super Cubs with it and know of a lot more on Pacers and Clippers as well and have not heard of any issues with the carb heat. Being in Alaska I definitely get the heat ribbons.
 
What I loved about it was ease of installation, no muffler AD, and lots of room behind the engine. Did not notice any performance change or excessive noise.

Should I be using lock washers on my brass exhaust nuts? I have lost studs, but never lost a nut.

of interest - CC converted the a/c to 180 hp, stock exhaust, and kept the almost new Sutton stuff. I insisted on an Atlee Dodge muffler - I absolutely hate doing that AD on a Super Cub. Hate it!
 
Hmm, I have not heard of this issue. Of course it rarely gets in the 20s and when it does and I am flying it is pretty clear and I don't remember pulling carb heat. Has anyone asked Brian Sutton about this? I wonder about closing the end of the shroud and putting pressurized air to it.
 
Would be interested to know if this is a ram air type system or suck air by the tubes and end of the muffler design of the Sutton.
 

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I have the same problem with carb heat on Sutton. Smooth surface muffler. I added some muff inlet restriction and that helps but it's still marginal at best below mid 20s OAT.

Gordon did you place the restriction on the air inlet to the muffler heat shroud (a single 2”) or the outlet, just past the heater and carb heat connections (two 2” outlets?). If it was the outlet what percentage of the outlet did you restrict?


Steve, have you seen a difference between those exhausts equipped with the heat ribbions and without? I have those heat ribbions on mine but I don’t remember if that is the later version or if I ordered it with some cold weather kit.
 
It also appears that if one shut the cabin heat off when the carb heat is applied the carb heat would get more hot air.
 
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.
 

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Gordon did you place the restriction on the air inlet to the muffler heat shroud (a single 2”) or the outlet, just past the heater and carb heat connections (two 2” outlets?). If it was the outlet what percentage of the outlet did you restrict?

I placed the restriction on the inlet to the carb air side of the muffler shroud. It helped considerably, but carb heat is still not as aggressive as I'd like. In difficult conditions, i.e. low OAT, I pull carb heat at cruise power, then immediately reduce power - sometimes to idle - to get the carb temp up. I have an EI carb temp probe and readout. I want to get 40F, when I pull carb heat.Carb Heat Restrictor Plate.jpg
 

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Carb air passes over the exposed end of the muffler can, hopefully, and over the #2 and #4 exhaust pipes going into the muffler. Heat ribbons will not increase the temp of the carb air as the carb air does not pass over that portion of the Sutton muffler. That is my recollection and I will confirm it when I get to the airplane.

To anyone with a carb temp probe and any exhaust system, I am interested to know what your temp probe display does with the application of carb heat. Up? Down? No change? PM’s welcome, Jim
 

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Most heat at low airspeed full power.
Pete, that's correct, but incomplete - only half of the process. First, note the difference between 'heat' and 'temperature'. Heat is energy, and temperature is a measure of energy per unit mass.

So with greater airflow through the muffler shroud, i.e. more air mass needing its temperature raised, more heat is required to raise the temperature of the air. For a given available heat from the muffler surface, greater temperature rise will occur with reduced airflow.

For that reason, the greatest temperature rise is obtained by running the engine hard, pulling carb heat and promptly reducing power to idle while the muffler is still hot. If you have a carb temp gage, give it a try.
 
CAR 3 suggests:

§ 3.606 Induction system de-icing and antiicing
provisions. The engine air induction
system shall incorporate means for the
prevention and elimination of ice accumulations
in accordance with the provisions in this section.
It shall be demonstrated that compliance with the
provisions outlined in the following paragraphs
can be accomplished when the airplane is
operating in air at a temperature of 30° F, when
the air is free of visible moisture.
(a) Airplanes equipped with sea level
engines employing conventional venturi
carburetors shall be provided with a preheater
capable of providing a heat rise of 90° F. when
the engine is operating at 75 percent of its
maximum continuous power.

Might be a reason for that spec.

Gary
 
Pete, that's correct, but incomplete - only half of the process. First, note the difference between 'heat' and 'temperature'. Heat is energy, and temperature is a measure of energy per unit mass.

So with greater airflow through the muffler shroud, i.e. more air mass needing its temperature raised, more heat is required to raise the temperature of the air. For a given available heat from the muffler surface, greater temperature rise will occur with reduced airflow.

For that reason, the greatest temperature rise is obtained by running the engine hard, pulling carb heat and promptly reducing power to idle while the muffler is still hot. If you have a carb temp gage, give it a try.

Note that your carb heat air does not flow under the muffler shroud with a Sutton exhaust. At least not around the muffler can in the way most of us expect it to. The shroud is extended out over the end of the muffler where the #2 and #4 exhaust pipes enter. The carb heat air passes by this area as it is drawn into the carb heat box by engine vacuum. Perhaps that might help explain your experience in post #46
 
This topic kind of threw me off. For one I don't get much carb ice in Lycomings. I only pull mine on pre-flight and when humid which isn't often around here. Also I get quite an rpm drop from my Sutton exhaust when I pull carb heat. I have been around airplanes long enough to know that there is a lot of PFM between two airplanes that appear exactly the same. For this reason I called Brian Sutton and asked him what he knew about it. Having maintained a couple of Grumman Tigers many years ago I knew he had pretty much used that design for this exhaust only tweaking it slightly for clearance with the cowl so that he could install the prop governor for his constant speed prop STC. I did not realize that the exhaust system is actually an Elano 100 design and used on almost 60 different fixed wing and helicopters. Brian did add the end plate to the muffler can where carburetor heat is drawn. He recalls having had one call with this issue. He did say there is a lot more carb heat from the stock Super Cub exhaust system. Brian enlightened me to some things about the system I had not thought about. The cold wetter air tends to get drawn to the rear cylinders and the drier air gets drawn down between the front cylinders and into the carb heat baffle. Something I had to think about and never realized.

My Dad and I talk a lot about mechanical things. He is a retired mechanical engineer and is the reason I got interested in how things work and fixing stuff. He lives in Memphis which has a fairly humid climate. He installed the Sutton exhaust on his Clipper via a field approval several years ago to get away from the exhaust AD and to get the muffler off the firewall and free up engine space. When he and I got caught in the arrival procedure gauntlet at Oshkosh this year, I was in my brothers Clipper, he was in his, we diverted to New Holstein to regroup. When we departed New Holstein he noticed I was running off and hiding from him which is usually not the case. This is when he noticed he had left his carb heat on. On our return triphome he didn't feel like he was making normal power and temps (UBG16 engine monitor and FP5L fuel flow) so we landed to check things out. We figured out his carb heat flapper valve was slightly open so we readjusted. I post this just to establish that in his application with a rear oil cooler and 160 hp O-320 he seems to be getting carb heat. He does not have a carb temp gauge.

Now, another piece of this puzzle recently when I was helping a friend order a Electronics International CGR30P engine monitor for his Cessna 180. We were discusssing the carb temp option and he told me about the inaccuracies of carb temp gauges as ooposed to carb ice detectors such as the ARP gauge that detects actual ice crystals. https://www.aircraftspruce.com/catalog/inpages/icedetect2.php?clickkey=25900 This was something else I was not aware of and made for some interesting reading. I do not know the answer to Jim and Gordon's issues but with all the information I have gathered the one question I have is have you actually gotten carb ice and if you did would the system not melt it?

Sorry if I have rambled but I have been sick for a week and still feel a bit impaired so some of this might not make any sense. :oops:
 
Pete, that's correct, but incomplete - only half of the process. First, note the difference between 'heat' and 'temperature'. Heat is energy, and temperature is a measure of energy per unit mass.

So with greater airflow through the muffler shroud, i.e. more air mass needing its temperature raised, more heat is required to raise the temperature of the air. For a given available heat from the muffler surface, greater temperature rise will occur with reduced airflow.

For that reason, the greatest temperature rise is obtained by running the engine hard, pulling carb heat and promptly reducing power to idle while the muffler is still hot. If you have a carb temp gage, give it a try.

Then the heat stops and the carb refreeze, now what?
 
Hmm, I have not heard of this issue. Of course it rarely gets in the 20s and when it does and I am flying it is pretty clear and I don't remember pulling carb heat. Has anyone asked Brian Sutton about this? I wonder about closing the end of the shroud and putting pressurized air to it.
Steve, ask S2D about carb ice and cabin heat in 37L. I remember it trying to quite one day with a little snow in the air when no other cub flying in close proximity was havin any trouble. I think he fixed it but don’t remember how.
Dave
 
One of the crashes of one of my Cub’s previous lives was due to carb-ice - noticed shortly after take-off. Application of carb heat put the cub into the trees.

I dont know much about it, but a mechanic told me there was a carburetor/0320 specific combination that was referred to as the “ice maker.”

I don’t think I have ever experienced carb ice, and mine is no longer the so called ice maker combo.

I can comment that my old leading edge exhaust caused a bigger rpm drop with carb heat applied than my Sutton does. Can’t really tell much difference in cabin heat.
 
I do not know the answer to Jim and Gordon's issues but with all the information I have gathered the one question I have is have you actually gotten carb ice and if you did would the system not melt it?
The short answer is I do not know. I have been suspicious of carb ice a couple times but unable to get the carb temp above freezing. So there was no way of telling for sure if ice was present. That was before I came up with the technique I mentioned.


Then the heat stops and the carb refreeze, now what?
Low power (not necessarily idle) only lasts a few seconds (10 max?). I go back to cruise power as the carb temp starts decreasing. Then the cycle can resume, but most likely not. Also, just because the carb gets cold doesn't necessarily mean it ices up right away. This is a technique that is effective, based on measured carb temperature.

One other matter I've encountered with the Sutton exhaust, that scared me pretty good the first time. The plane had been setting out in the rain and wind for a couple days, facing into the wind. I took off from my hayfield, and in climbout pulled carb heat as a precaution, because it's the still-cool engine that is most prone to carb ice. The engine quit immediately. It didn't cough or stumble, it quit. Over hostile terrain at fairly low altitude. I pushed the carb heat back in and the engine came right back at full power. I determined that water had blown in the nose bowl into the engine compartment, thence into the heat muff. It happened one more time in the same circumstances, but I was suspicious it might happen and I was ready. The lesson - do the carb heat part of the runup at high RPM and pull carb heat gradually, so that any water gets sucked up from the bottom of the muff gradually. Another solution might be a small drain hole in the bottom of the muff.

Overall I like the Sutton exhaust and I'm not trying to bash it. But carb heat is indeed an issue. I think there might be a way to add baffle(s) between muffler and shroud to increase the carb air's contact with the hot muffler.
 
I guess a STC should still comply with whatever regs the aircraft was originally certified under (like the CAR 3 carb heat temp rise above). Or if that's not the case how do they obtain and document any deviation for others to know? I have no opinion of Sutton's systems.

I've suggested before adding a manifold pressure gauge as a quick indicator of an induction restriction...both on the air filter when flying in visible moisture or snow and in the carb. It does work if we pay attention to the instrument in level flight at constant power. The link in #47 supports that.

Wrap an annealed door spring around the exhaust for more heat.

Gary
 
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Thanks for your input Steve and taking the time to call Brian. If he claims one call, I will take credit for it. I will be polite and say it did not go well from my point of view.
As to his points about the cold, wetter air going to the rear cylinders and drier to the front, two points. Would like to see the data on that and even if it is accurate, I do not understand his point. Please clarify.
i do not know anything about carb ice detectors. I have a carb temp probe. I flew today. 20 degrees F ambient temp. Runup at 1700 was a feeble 20 rpm carb heat drop with an EI tach. An hour into my ride my carb temp was showing 64 degrees. Full carb heat for 5 full minutes did not change that temp one degree. Am I confident in this system being able to clear carb ice. Nope. My experience, Jim
 
points about the cold, wetter air going to the rear cylinders and drier to the front, two points. Would like to see the data on that and even if it is accurate, I do not understand his point. Please clarify.
I agree. If Brian is on here perhaps he could clarify?
 
A quick search of what an “Elano” exhaust system is revealed that this style muffler has been used on various airplane types. The Cessna 152 muffler/system looks remarkably similar to the Sutton system with one exception. The shroud has 4 scat attachment points. I assume they take the carb heat feed off the muffler can with ram air. Cessna is dealing with an 0235, perhaps the heat is not adequate with the smaller displacement engine.
 

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I remember hooking SJ's carb heat up backwards one time. He had great carb heat and poor cabin heat. Might be an interesting test to see what your carb temp gets to.
 
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
I was in error and you are absolutely correct. I was not aware of the baffle in between the cabin air vent and the carb air vent or that the carb air inlet is at the opposite end of the muffler If the Sutton is short of carb heat is likely because there is such a sort distance for the heat exchange to take place.

I cant help but wonder what would happen if one ducted some of the ram air from the cabin heat to the carb heat. Carb heat is not in my experience ducted under pressure and I have no idea what that would do.
 
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