FYI: Exhaust radiant heat

[Clint B]

Originally Posted by Gisnar

Do not want to hijack this thread (if this question needs to be moved great!).
But, what has been the experience with ceramic coatings and wrapping the exhaust on our little piston engines?

We got an exhaust back for repair once that had the "header wrap" Where the pipes branched together, it looked like someone had been beating on in from the inside with a ball peen hammer, and all of the slip joints had welded themselves together. Needless to say, those pipes went in the scrap bin.

[dougmattson]

Originally Posted by BillL

When I ran a dyno in the lab, one day my cell neighbor (common control room between cells) was running maximum power at peak torque ( diesel past regulated fuel) and it was about 1400F for a while getting the data point. I know it was not true, but I swear it looked like you could see the turbine wheel turning through the housing.

Neat stuff, and reminds us why we have shielding FWF for critical things that don't like to be hot.

Thanks for sharing!!

I used to work in a diesel dyno lab also. I believe you can see thru the turbo housing and see the turbine wheel.

[RV8RIVETER]

My exhaust is ceramic coated. All is good so far, though on very low hours.

I haven't heard any valid reason why not to coat, yet. Why have all that heat energy radiating into the cowl? With half the stock inlet opening my CHT's are in the very low 300s.

ADDED: By listing my CHT numbers, I did not mean to imply coating would decrease CHT's. Only that they have no bearing on mine. I haven't seen any data that they have any significant effect on CHT either way.

[Toobuilder]

I also ran ceramic coating on my mild steel header. 400+ hours, no problems at all.

[Kyle Boatright]

Originally Posted by RV8RIVETER

My exhaust is ceramic coated. All is good so far, though on very low hours.

Coated internally or externally? I makes sense to me that internally coated pipes would help cool the cylinders, pipes, and the engine compartment, but externally coated pipes might result in higher temps at the exhaust port flange and in the pipes.

I can't see where an internal coating would have any downsides, but I tend to defer to the recommendations of the manufacturer who recommends no coatings.

[Toobuilder]

I used the Jet Hot 2,000 degree stuff (flat black, rough finish) on the outside only. Still looked like new when I sold the airplane. No issues with cylinder head temps before or after the coating.

[AlexPeterson]

Originally Posted by Kyle Boatright

Coated internally or externally? I makes sense to me that internally coated pipes would help cool the cylinders, pipes, and the engine compartment, but externally coated pipes might result in higher temps at the exhaust port flange and in the pipes.

I can't see where an internal coating would have any downsides, but I tend to defer to the recommendations of the manufacturer who recommends no coatings.

What is the theory that says that coated pipes would result in cooler cylinders?

Speaking of theories, what is the physics reasoning behind coating pipes in the racing world?

[Toobuilder]

Originally Posted by AlexPeterson

...Speaking of theories, what is the physics reasoning behind coating pipes in the racing world?

Maintains exhaust velocity through the entire header. The temperature difference between the exhaust port in the head and a thin wall header can be significant. Enough that it's like hitting a brick wall and can create a reflected wave back to the valve. This is what I've read, anyway.

[rocketbob]

Originally Posted by Toobuilder

Maintains exhaust velocity through the entire header. The temperature difference between the exhaust port in the head and a thin wall header can be significant. Enough that it's like hitting a brick wall and can create a reflected wave back to the valve. This is what I've read, anyway.

Correct. As the gases cool significantly in the exhaust system it restricts the flow. The only way the pipes cool is to dissipate heat from the pipe. Most Indy car exhausts have the outside coated only since longevity is not much of a concern particularly with stronger pipes made from Inconel (which is a really awesome stainless material but absolutely a pain to cut.) To help a lower grade of stainless to survive longer with more heat retained the inside needs to be coated.

[Bavafa]

Mine are also coated since new and no issues so far in 440+ hours. My top cowl is far hotter to touch than my lower cowl but I also have insulation on my lower cowl which probably is the main reason.