Thermal exhaust wrap

[tx_swordguy]

I do not know the effects on airplanes, however on motorcycles wrapped exhaust was/is a style kind of thing. Problems are more related to moisture being either held or retained on the exhaust pipe and then cooked off during heat cycle. (motorcycle exhaust is exposed to water on the road and during washing much more so than an airplane) Not 100% sure of the how, but what is happening is the pipes end up rusting from the outside much quicker (even when chromed). Vibration + moisture+ heat all rubbing the outside of the pipe = rusted pipes. It seems much worse on the header part where the most heat is. I think if you can shield parts you want shielded you would be better off. That being said if you don't wash or get the wraps wet, it may not even be an issue.
Mark

[jrthomas]

Answer for KFfan. Quoting from Roger: "Bottom line, it's up to you but the wrap shouldn't hurt anything if it's installed correctly. By that I mean that the edges are not over wrapped by (more than) 3/8". If it gets over wrapped by half way then that's too thick and heavy and it will retain too much heat." James Thomas

[Kurt.A]

The very first time that I seen exhaust wraps was in a turbocharged automotive application. I discussed the theory behind it with the owner and was told that a Turbocharger is actually a heat pump. By that statement he meant that it was not the flow of exhaust gas that spins the turbine wheel but the expansion of the exhaust gasses that spins the turbine. I have since read over and over that this is the true theory behind turbocharging. With that in mind I can certainly see that holding the heat inside the pipe prior to the turbo would increase the efficiency of a turbocharged application. With regards to a naturally aspirated eng the proposed merits is that the exhaust gasses have a higher velocity which may assist with better scavenging of the exhaust from the cylinders. In my opinion an insulated exhaust system has eng performance merits to be considered along with reduced under cowl temperatures thereby allowing your cooling system to be more efficient. With regards to the negative aspects of reduced exhaust system life that is for each to evaluate. My 912 came to me with exhaust wraps, I see no signs of abnormal degradation in the 700 hrs on the clock.

[jrevens]

Kurt,
With all due respect to you and the person you talked to, it certainly is the flow of exhaust gases that spin the turbine. It is the pressure differential between the inlet and outlet of the turbo that increases the velocity of the gases flowing through it and increases the kinetic energy of the gases that are impacting the rotor blades and driving them. If the exhaust gases leaving the engine can be kept from cooling off before they reach the turbocharger by wrapping, then they will remain at a higher pressure than if they were allowed to cool (all things being equal), which will result in a greater pressure differential and more potential kinetic energy driving the rotor. That being said, I believe that the difference in performance is probably tiny in this instance. You'd have to test the engine on a dynamometer to see. On the other hand, wrapping the pipes downstream of the turbo will increase the temperature and potentially the pressure of the exhaust gases in that part of the system, which could decrease the differential across the turbocharger & decrease efficiency. There are many other factors that come into play of course. IMHO, the only really practical reason to wrap would be to decrease temperatures in the engine compartment.
700 hours is a good long time and a testament to the probability that there is no harm being done to your system. I'm curious though - have you un-wrapped it to see if any corrosion is occurring on your pipes? Stainless steel is much less vulnerable to it in this instance of course. I wouldn't even consider wrapping if I had a mild steel exhaust system, but that's just my opinion.

[KFfan]

Answer for KFfan. Quoting from Roger: "Bottom line, it's up to you but the wrap shouldn't hurt anything if it's installed correctly. By that I mean that the edges are not over wrapped by (more than) 3/8". If it gets over wrapped by half way then that's too thick and heavy and it will retain too much heat." James Thomas

James
Thanks for the clarification

[jmodguy]

Theres a guy in FL that has a Rotec radial on a RV-8. He wrapped his exhaust and somehow it got some oil on it. Nearly caught fire so he pulled it all off. Yikes!

Jeff

[Kurt.A]

Kurt,
With all due respect to you and the person you talked to, it certainly is the flow of exhaust gases that spin the turbine...

John you typed what I wanted to say far more eloquently. I definitely used the word flow in poor context. I did unwrap the exhaust and took a pic of the results for you. One part of the equation to take note of is I am the third owner. The person I bought from did say that the exhaust was wrapped when he bought the plane at 400 hrs.

[jrevens]

Thank you Kurt, although I don't think I did a very good job and I'm sure there are some inaccuracies in what I said, but I appreciate your kind words, and being able to see the unwrapped pipe... it looks pretty good, doesn't it?