Dont wrap your exhaust!

[Shadowrider]

I will post some pictures later, but I would advise against wrapping your exhaust on a rotax. We are in the process of replacing both our exhaust on our STI's because the exhaust has collapsed.

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwiz-tu80v__AhWwOkQIHUuDB7MQFnoECA0QAQ&url=https%3A%2F%2Flegacy.rotaxowner.com%2Fsi_tb_in fo%2Fserviceletter%2Fsl-912-025.pdf&usg=AOvVaw1_bL-rNKiTFvP0k4rcFW1O&opi=89978449

[tracstarr]

Very odd to see this today. I just wrapped my exhaust pipe and 1 down tube to test. My cowling temps are in the 60C range on a hot day here. I'm also working on a cold air intake because I just can't fly due to the temps under there.

I'm curious how long have you had it wrapped and is it getting wet somehow? I've read a lot of the Rotax owner forums and I found the general consensus was go for it. If done right it should be fine. Several have suggested they've had it done for a long time. I've seen that SL as well.

Interested to see those pics and also interested to see if my testing actually shows any difference in the first place.

[Shadowrider]

I can tell you, even if you do it correct you may still have problems? I think there is apple to oranges being compared on the forums so take that at a grain of salt. 912ul and 912is exhaust temps are very different. On a 912ul or 912uls you may be okay? For sure I would not do it on any turbo engine, 914,915,916, and I dont think I would do it on the 912IS. What kind of egts are you seeing? IS engines run so lean the exhaust is extremely hot. I even richend my map up so I was not seeing over 1450F egts, but my exhaust still collapsed. I have about 200hours on my exhaust so it doesn’t show up right away. Slowly starts to collapse. Exhaust wrap keeps the heat in, which is good for a turbo, makes more power, but the exhaust can't hold up to it. 2 of the 4 headers collapsed. What I think is happening is you actually shock cool the exhaust. Cylinders 1 and 2 exhaust collapsed. I think as you are flying the wrap keeps the heat in and they get too hot. Then you pull power and the front of the exhaust cools quicker, because of direct airflow, than the rest of the exhaust that has been insulated and now the temp differences causes the exhaust to collapse and warp. Interesting it happened wright where the egts are attached? Its also causes the exhaust to warp and become misaligned. The gains you will see is not worth it IMO.

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https://lh3.googleusercontent.com/pw/AIL4fc8pYBy9Apow61epnrrFFFSHhq8lPWoMpNXK292GSkQU-YS4eg66V3HSDyYAvSjADxlmGQCC36BU6gvbihzSTPL_1riS6px tXpv6c--WD3HPTMD0A6Sggc-nZ4tWLMXTDqytxjwv6GuvtK7m4sQDL1Nj3Q=w764-h1019-s-no?authuser=0

https://lh3.googleusercontent.com/pw/AIL4fc-vELSuldcmalDCc9lQoFBXViPWMi3_82xoPSLRIal1Dxuwjrqyr g0vPckiD6n7xweCALJtekh1rZ11iOPrca5tWi6fLHfwvVuenzI SO8BcanESIuBdFq3rDirECItpc5TGOI6grOL9oUefrsl8b__hE U13l5gTr5MHZ7T8XzTQyWqMqX2RmzArcbh9WuqNAI4BBOZawmZ EWafHROwC5i4-0N5w4usSt3D4852o-_muTkJkipqJ9GPoWYfSMQBMCIGAG0tYOazAGAVOA7fVuUgo3kW o1TvUAKEAvatcUzDgb3oxBCdDmPRcnyqmJJFTBq7N87LcTHJTL z6jSdldAbN4jOZFK3LSzAYsR1-zPLECh3G3mSosrBCVg7sUPk6R3Qr4lwzZCLh1FhhkpKs8h2ST0 sreJBBNk5IXpitIGo-uHQAZVblR-ooFRfuH2cK_2wEhg0k1ndk9AeyNEjP79LvtFfOavCXVmTkLCi5 VabIS1RP9geiaKFpHBMr_4ZmNc-lTBvDKPz4UPyBQ2jWPAbH8nddpT1Zs93cVpjFpVnsrk7J4k1x6 PeIbQjuT_77FEfvw2pxjSqHQWWee0zNkubEITtL2Ar7iIfCcNL fAYAV5sX44Md4hu7NgoyP12GZWg600TiXQ2-qF1jZYpKu3KcbWgI_xoPLbIDxkDslu3B_0rc1rM7LivM9yJ2hf F2gOu-3najfj7MMc-nO6TpTNpLY5zgJGvjZ5VI8snu91TurbRbDjVmZMtaYxipNv1-xzH86RqlSUsAAV3tyGfidyNEL5ppbbb2f-eISV5EVCTGavU0ljYe55dXw5tXglRRcRttPlNrHBBsgK1qkqQ-0jX1J0GtNBDuY8EDk31Xj0iaszSHM_dJeflgcrFeWLHFUHLdFZ 4wP5PYMXQtMZZRFS5PUbGdlVzk56G7e1LwuV9ghDuzPjaDkCx1 Q9VUwU0w=w1359-h1019-s-no?authuser=0

[buckchop]

Well im no pro on wrapping the exhaust on mine or any plane, but i kind of think u have something else causing that problem with ur exhaust collapsing, How many other guys have ur same setup? R they havin the same under hood temp problems? Ive wrapped many snow machines, race car, Harley, triumph, street rod exhaust in my yrs of fun never had any problems, love the stuff and wouldn't hesitate to put it on either one of my planes.

[Billiken]

I appreciate you sharing this valuable information. I’m kind of following in your footsteps. Please keep us informed of what you decide to do.

[Dusty]

We have the same problem on a customers UL ,I don't know the full history but it has standard jetting.
My ul runs 1500 f with std jetting & no wrap, no warping.What is the yield temp of exhaust grade ss?

[atosrider]

I wrapped the #1 912UL pipe in the model 3 fake radial cowl, due to minimal clearance to the oil supply line to the pump, so I'm paying attention here.

I liked the shock cooling theory, no how about a theory for only the front tubes being effected. With the fake radial cowl I can imagine better cooling air circulation for the rear two pipes.

there are many chances for differences in our setups. I have removed the carb heat muff on #2 and closed in the gaping hole in the cowl because electric heaters are installed in the carbs. mmmm more air flow over the top of the motor?

this morning it was 85oF outside air temp and egt was 1300 on climb, but the probes are far away from the cylinder head (as per Westach quad gauge instructions circa 1992) with this high outside air temperature it was interesting to read 160oF for oil (wish it was easier to lower the rad for reduced air flow) and that might help the cylinder ("water") temp reading of 190 which given that this is as hot as it gets that is not a problem (other than looking ugly hanging under the belly, doesn't that leave things open for comment)

[Shadowrider]

Well im no pro on wrapping the exhaust on mine or any plane, but i kind of think u have something else causing that problem with ur exhaust collapsing, How many other guys have ur same setup? R they havin the same under hood temp problems? Ive wrapped many snow machines, race car, Harley, triumph, street rod exhaust in my yrs of fun never had any problems, love the stuff and wouldn't hesitate to put it on either one of my planes.

Enough "rotax" "guys" have had a problem with this that Rotax issued a SB advising against it and stating those that do will not be covered under warranty. (Even though I think warranty does nothing for you in the back-country) I don't know how many it takes to issue a SB but I am guessing more than a handful? They are also stating not to use ceramic coatings. I think your comparing apples to oranges here as far as stating it works on a Harley ect? Experience shows on most motorsports that exhaust wraps and ceramic coatings work great. On a rotax, our experience confirms exactly what rotax is saying, that you will possibly have shorten exhaust life including possible exhaust header collapsing.

[Shadowrider]

We have the same problem on a customers UL ,I don't know the full history but it has standard jetting.
My ul runs 1500 f with std jetting & no wrap, no warping.What is the yield temp of exhaust grade ss?

Interesting! My guess is the IS series, 912IS and 915IS probably have more issues because they are seeing higher EGT but I guess the UL series have also experienced issues with wrap.

[jrevens]

I'm working off memory now, but I believe the maximum temperature to avoid issues such as corrosion resistance and loss of strength is around 1600 deg. F, for 321 SS. 321H is slightly higher I believe. 1500 max. is desirable. Just off the top of my head, the "bung" welded on, right at the bend, could possibly introduce unequal stresses as the tubing heats up & cools down. Also, obviously, a well-designed exhaust system usually needs slip joints and sometimes ball joints, located to minimize stress. I don't mean to imply that this exhaust system isn't well- designed in general... I don't have any idea what the rest of the system looks like, or what material it's made of.

[Shadowrider]

John look up what the max EGT on the 912is and 915 of and it may surprise you. Then ask operators what the normal temps they are seeing? Basically glowing bright red. (915is is 950C (1742F) Exhaust in the picture has never seen over 1450f. Edge improved the exhaust from the stock rotax. Rotax last 20 hours before developed exhaust leaks.

[13brv3]

I recall reading that 304SS only has 20% of it's strength at 1400F. Seeing bent pipes makes me wonder if there was some sort of bending stress on the pipes that was more than they could withstand when they were hot.

As for wrap, I used it on a 912UL, but it never lasted more than about 15 hrs before starting to crumble.

Rusty

[Kitfox Pilot]

1610 is about the top egt, 1575 is normal for cruise in a 915is. Having egt gauges on most of our farm equipment, these 1600 degree numbers scare one when you first see them. 220 hours and no melt downs yet and everyone assures me this is normal for the i s engines.

[jrevens]

I recall reading that 304SS only has 20% of it's strength at 1400F. Seeing bent pipes makes me wonder if there was some sort of bending stress on the pipes that was more than they could withstand when they were hot.

As for wrap, I used it on a 912UL, but it never lasted more than about 15 hrs before starting to crumble.

Rusty

That's probably right. 321 or 321H are better choices for exhaust systems. It is basically type 304 with the addition of titanium. 321H also has a higher Carbon content. Additional stresses are exactly what I was talking about, with the welded fitting right at the apex of the bend, slip joints, etc.

Justin... no it doesn't surprise me. With those kind of temperatures, maybe you should be using Inconel. It's only money. ;)