There is no doubt that reducing under-cowl temps provides many benefits - longer electronic component life, reduced chance of fuel vapor-lock, and reduced cooling requirements, to name a few.  Also, due to a carb mod I did, I had to install a small cabin heat muff on my exhaust pipe immediately as it exits the muffler, rather than being installed on the muffler itself.  My theory was that insulating the muffler (and the cabin heat muff) would retain the heat further down-stream and help produce more cabin heat.

Initially, I used a quality exhaust wrap on the muffler and heat muff.  Last winter, this seemed to distinctly improve the performance of my cabin heat!  However, most exhaust wraps are really not permanent - the direct contact to the very hot muffler steadily deteriorates the wrap.  I noticed the wrap on the muffler was beginning to become fragile and was concerned about any wrap potentially coming-loose due to deterioration and causing havoc under the cowl - that's no place for loose pieces of debris!  However, the wrap on the cabin heat muff on the exhaust pipe exiting the muffler seemed to be holding up much better - looked like new - probably due to the lower temps at that location.

I therefore decided to try a different product on the muffler - Heatshield Products "Heatshield Armor" Exhaust Insulation.  This product has a dimpled 4 mil aluminum outer cover bonded to a .25" ceramic insulation blanket (not fiberglass).  It is designed for direct contact to exhaust surfaces and can withstand 1800F continuous heat and 2200F intermittent.  It supposedly reduces radiant heat 60-70%.

I templated the muffler with thin cardboard and then transferred this to the heatshield material.  Since the material is a 1/4" thick and would not roll up as tightly as the template, I knew the material would have to be slightly over-sized. I compensated for this by clamping the template to one end of the material, rolling it around a 5" diameter can (same diameter as my muffler), and marking where the other end of the template terminated.  For a neat appearance, you can strip about 1/2" of insulation off the edges and bend the foil back over to give a finished edge with no insulation exposed, so one must allow for that also when making the template. I also allowed for some overlap when wrapping around the muffler so I could tuck one end under the other and this would allow for slight errors in measurement ... this stuff is pricey (I paid $84 for a 2' x 2' piece!), so "measure twice and cut once" is the rule! 

Normally, it is held in place by stainless zip ties, but my exhaust system has two stainless bands that wrap around the muffler to retain springs on the exhaust seals - these worked perfectly to hold the shield in place.  I made 5" round pieces for the ends and simply crimped these in place with over-hanging foil from the wrap around the muffler.

I did a run-up and the product seemed to do well - no smoking or fumes as is sometimes encountered with fiberglass insulation.  My EGT's are typically in the 1300F+ range, so the muffler temp should be well below the 1800F continuous rating for the material. 

Obviously, long-term durability is yet to be determined, but it should hold up well according to numerous positive reviews.  I'm going to see how it performs this summer and if there are no problems, wrap the cabin heat muff as well with the leftover material.  BTW, my entire exhaust system is stainless steel, so I don't anticipate problems with corrosion - there was not a bit of corrosion found when I removed the previous exhaust wrap.

I thought this might be of interest to any concerned about under-cowl heat. Although I have the new puck suspension system, it might be particularly useful to those with premature bungee failures that could possibly be heat-related.

John

N750A

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Curious as to why you chose not to wrap the pipes leading to your muffler.

I was primarily trying to accomplish two things: Reduce radiant heat to the carb (the AeroInjector carb is sensitive to heat and subsequent vapor formation) and boost heat to the cabin heat muff on the exhaust pipe downstream relative to the muffler.  To me, it made the most sense to insulate the muffler and the cabin heat muff.  The headers between the engine and the muffler are short and have a high-velocity flow - insulating them would probably have minimal effects on my desired objectives.  Once the exhaust flow reaches the much-larger diameter and much-greater volume of the muffler, the flow slows and there is a greatly increased surface area to absorb and radiate heat.  Also, the carb and intake runner are just above and behind the muffler and relatively distant from the headers, so the muffler radiates heat directly to this area while the headers are well forward and lateral to the carb/intake runner area. For these reasons, it seemed best to insulate the muffler and cabin heat muff.

I saw a distinct improvement in cabin heat from insulating these areas and have zero problems with vapor in the carb or fuel line.  Therefore, I don't think there would be any meaningful gains from insulating the headers, plus, insulating this area is much more complicated and difficult and would obstruct inspection of a large area on the sides of the engine.

John

John,

Any thoughts about wrapping the exhaust pipes.  I have a Rotax 911 ULS setup but I suppose any heat you could keep out of under cowl areas would be good.

Any other of you wrapped the pipes esp on the Rotax motor...what was your experience.

Still Grinin

Phil Smith

Ch 70wonderful

Buhl, ID

The overall under-cowl heat did not seem to be a problem and I was primarily trying to cut direct, radiant heat to the fuel system (all located behind and above the muffler on my Jab 3300) and boost cabin heat efficiency by insulating the cabin heat muff which is attached on the exhaust pipe where it exits the muffler.  So, as explained previously, I didn't see much benefit to insulating the exhaust headers.  The exhaust pipe exiting the muffler is covered by the insulated cabin heat muff and also the muff has a ducted constant airflow that is either dumped overboard if the heat is not in use or directed by a valve to the cabin for heat.  Once the pipe exits the muff, it's mostly below the cowl opening, so no need for insulation there.

I have heard Rotax owners attribute premature bungee failure to heat.  I recall at least a report or two of builders fabricating a heat shield to protect the bungee from radiant heat, but don't recall a follow-up report as to the effectiveness.

John

John,

Thanks for your input - just fishing around for those who have wrapped their pipes and what they saw "under hood".  

I have switched to the "Viking Spring" nose bungee - like it alot.

Here in Idaho it gets pretty hot in the summers so I've added an "air dam flare" to the outlet at the bottom of the cowl al"a Cessna air dam on their old 172 seaplanes. Fabricated an air scoop for the front of the radiator.  Also added a fiberglass scoop to the NACA Duct on the oil cooler inlet. Each added a little bit of cooling and the whole shebang seems to have helped on a really hot day.  (all discussed with pics in a previous post on my site)

Still grinnin and flyin!!

Phil Smith

Ch 70wonderful

Buhl, ID

The Heatshield Armor has been performing well for several flight-hours so far.  I removed the cowl for maintenance yesterday and found it exactly as I had left it - no evidence of heat discoloration, no burnt odors, etc.  However, I did a run-up on the uncowled engine and the round piece of insulation on the right end of the muffler came loose - the left looked a little loose, too.  Apparently the prop blast had got under the insulation where it is exposed around the headers entering the muffler and lifted the end-pieces of insulation slightly - the crimped aluminum was not strong enough to hold it in place.

With the cowl installed, I think it would be OK, but of course I routinely do uncowled run-ups after oil changes and other maintenance, so I needed to secure the end-pieces somehow.  I secured a stainless zip tie around the very ends of the muffler to hold the crimps a little tighter against the end-pieces and used stainless safety wire to hold the end-piece against the end of the muffler.  I used existing spring anchors on the exhaust to run the safety wire through and then down and around the spring-band securing the exhaust seals:

Please ... no jokes about "baling wire and chewing gum" repairs!  ;>)

The insulation stayed quite secure on a subsequent run-up.  BTW, when I was re-securing the round piece of insulation on the muffler end, I was very pleased to see that the ceramic blanket on the interior was not at all scorched or melted - looked almost the same as new!  Apparently it really will withstand direct contact to the hot exhaust, so I'm optimistic for the prospects of long-term durability.

John

Has anybody tried using ceramic coating on win side of exhaust pipes like race cars sometimes use

Ironically, many years ago I had a '73 DeTomaso Pantera that I sent to Pantera Performance Center in CO for a restoration.  They sent the headers to "Jet-Hot" for ceramic coating inside and out.  The insides were as smooth as glass tubing and the outside impervious to heat discoloration, etc.  It definitely improves exhaust flow and claims to decrease radiant thermal heat.  I definitely would do it again for a high-performance engine both for function and appearance, but as stated earlier, my Jab's headers weren't in a position where they were directly radiating heat to my carb and fuel lines (as opposed to the position of my muffler relative to my carb), so I don't think it would have made much of a significant difference in decreasing radiant heat to the carb.

John

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