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FYI: Exhaust radiant heat

G3i Ignition

Well Known Member
Yesterday doing a dyno run @ G3i facility on a new concept exhaust system for ?Vetterman Exhaust Systems?. At 100% power the pipes started to turn cherry red @ 1300f and lean for peak power 1440f bright red/orange. Should of flip the lights off for moment, would have been a good pic. We took a few pics of it for the curious. The example shown is to make aware of the radiant temps that are inside the cowl and components are subjected to. That?s all?.Go Bronco?s
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It would be really interesting to see what happens to CHTs if one has the insides/outsides ceramic coated.

Easier said than done on used pipes.

Its nearly unheard of in the racing world to run uncoated pipes.
 
Just a curious thought as I have absolutely no prior knowledge, but wouldn't air moving through the engine compartment keep those pipes quite a bit cooler?

It seems that in a test cell you likely don't have that kind of airflow over them. ??????
 
It would be really interesting to see what happens to CHTs if one has the insides/outsides ceramic coated.

Easier said than done on used pipes.

Its nearly unheard of in the racing world to run uncoated pipes.

even on air cooled engines?
 
Ceramic coatings

On the Vetterman exhaust website there is a paragraph under FAQ entitled "How about ceramic coatings", implying they keep heat in the head. No numbers quoted though.
 
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 have occasion to fly a Piper Navajo. A section of the exhaust was visible through a vent on the side of the cowling. After dark this would glow pretty good even at altitude in cold temps. I do not know if it was any special metal or not. I think some of the Cessna twins had their pipes made out of iconell or something special to stand the heat but I do not remember hearing that about the Pipers. There is a lot of heat there for sure!
 
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?
 
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.
 
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.
 
mine are

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

I don't think the metal becomes transparent...I believe you were seeing the "shadow" of the cooler turbine wheel on the blackbody-radiating housing.
 
pros and cons of ceramic coating your exhaust

Pros: All your rubber bits under your cowl will last longer without all that heat, slight increase in power

Cons: You can never weld that exhaust again
 
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.
.

Coated only on the outside. I wanted both sides coated, but the coating expert was adamant that they only be coated on the outside. He had dyno runs that showed higher hp with only the outer coated versus the inner as well.

Mine were Zirconium coated, which was claimed to not be problem welding any future repair, but since I have not tried or known anyone who has, I do not know if that is true. If they need to be replaced I will go with a home made mild steel copy and coat that, cheaper than stainless.

Also, I edited my previous post to make sure my last sentence wasn't taken the wrong way.
 
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When coated, by collector was a slip fit for all four pipes. Shortly thereafter I welded one of the primary tubes to the collector to lock it in position. No issue with cleaning off the ceramic and welding.
 
Pros: All your rubber bits under your cowl will last longer without all that heat, slight increase in power

Cons: You can never weld that exhaust again

Ironically, my exhaust was welded by Wetterman as part of a recall they had for this specific model. It has held up very well so far. They did not make any comment about welding it, if it was harder/easier or different.
 
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?

I have been told by an exhaust fabricator that the exhausts "wick heat away from the heads" and that this and welding are impaired by the ceramic coating.

It seems to me that the exhaust runs several hundred degrees hotter than the head, so any heat transfer would be into the head rather than out of it. A ceramic coating on the outside would make the metal of the exhaust hotter by reducing heat transfer to the airflow in the engine compartment, so there may be some validity to that argument. An internal coating would seem likely to make both the heads and the engine compartment run cooler though.

There are three stated benefits to the ceramic coating:

1) cooler heads and engine compartment. An internal coating should do both of these, an external coating (or wrap) still cools the engine compartment and might make the heads hotter, although I'd guess that's a pretty small effect given the difference in mass of the heads and exhaust, and the fact that there is already a gasket between them.

2) More horsepower, presumably by reducing the temperature/pressure difference as exhaust gases enter the pipe. I don't quite understand this one, it seems to me that rapid cooling would drop the pressure in the pipe and reduce backpressure, but there is lots of empiric evidence in cars and airplanes that it works. I do understand how it would increase the "jet" effect of the exhaust, as the exhaust gases ought be be hotter, and faster leaving. Any ceramic coating (or wrap) should do this.

3) It looks better, presumably causing attractive women to want to hang out around your RV. Given the already very powerful effect of the RV airframe, I'm guessing any incremental effect from the exhaust is going to be pretty small. Obviously only an external coating would have any effect on this parameter.
 
Jet hot

Very interesting. I emailed jet hot to find out a little more on how they do the exhaust they replied back that they would coat the inside and outside of the exhaust. Which seems like the correct way to do I am not sure how much weight it's adds.
Tim
 
Back when I did mine, Jet hot offered the satin silver finish typically seen on car headers. Jet Hot's literature indicates this stuff is good up to about 1350, IIRC. I called the company and told them that I'd be subjecting my exhaust to approximately this temp, but for hours on end. Jet Hot suggested this product would not survive. They steered me to their high temp coating which did last fine. I only bring this up because it has a very rough finish, about like #40 grit sandpaper. I think this roughness would be bad inside the pipes.

That said, are people having good luck with the shiny, smooth silver product?
 
2) More horsepower, presumably by reducing the temperature/pressure difference as exhaust gases enter the pipe. I don't quite understand this one, it seems to me that rapid cooling would drop the pressure in the pipe and reduce backpressure, but there is lots of empiric evidence in cars and airplanes that it works. I do understand how it would increase the "jet" effect of the exhaust, as the exhaust gases ought be be hotter, and faster leaving. Any ceramic coating (or wrap) should do this.

On large yachts, and smaller for that matter but in particular on the large ones with large diesel engines and/or turbines, water is injected into the exhaust to reduce the velocity and reduce friction. The friction is proportional to the mass flow times the velocity. The mass flow is constant regardless of velocity, while the velocity will be greatly reduced when the density increases. Water injection also nearly removes all noise. There is a huge industry revolving around this, which a friend of mine is working with.

I don't know what exactly is meant by the "jet effect". If the exhaust flows inside the pipe at constant density, there will be a reflection only at the end where the pressure is constant, a pressure node. At that point the flow will have an antinode, or a max amplitude point when the pulses from the engine resonates with the frequency of the hot gases inside the pipe, like a flute. It sure will make lots of noise, but if the power will increase? maybe, I don't know. Maybe it somehow will help evacuate gases from the combustion chamber?
 
2) More horsepower, presumably by reducing the temperature/pressure difference as exhaust gases enter the pipe. I don't quite understand this one, it seems to me that rapid cooling would drop the pressure in the pipe and reduce backpressure, but there is lots of empiric evidence in cars and airplanes that it works. I do understand how it would increase the "jet" effect of the exhaust, as the exhaust gases ought be be hotter, and faster leaving. Any ceramic coating (or wrap) should do this.

Much of the flow in exhaust pipes is supersonic. Supersonic gas flow and the related shock waves have some characteristics that are counterintuitive to what we know about subsonic flow. One example is that nozzles behave oppositely for subsonic and supersonic flows. Ever notice that rocket nozzles are divergent, i.e. there area increases in the direction of flow? For supersonic flow, the gas velocity actually increases through the nozzle, while divergent nozzles are used to decrease the velocity of subsonic gas flow.

Anyway, some of these same effects occure inside exhaust pipes, and keeping the temperature of the exhaust gas elevated is all about maintaining supersonic gas velocity and controlling the related shock wave.

Skylor
 
Has anyone here actually done a dyno run, swapped for coated pipes, and done another dyno run?

Methinks a promise of more power is a better sales pitch than "Your headers won't rust so quickly." ;)
 
SNIP
3) It looks better, presumably causing attractive women to want to hang out around your RV. Given the already very powerful effect of the RV airframe, I'm guessing any incremental effect from the exhaust is going to be pretty small. Obviously only an external coating would have any effect on this parameter.

Finally, some science has been brought into this thread!
 
Much of the flow in exhaust pipes is supersonic. Supersonic gas flow and the related shock waves have some characteristics that are counterintuitive to what we know about subsonic flow. One example is that nozzles behave oppositely for subsonic and supersonic flows. Ever notice that rocket nozzles are divergent, i.e. there area increases in the direction of flow? For supersonic flow, the gas velocity actually increases through the nozzle, while divergent nozzles are used to decrease the velocity of subsonic gas flow.

Anyway, some of these same effects occure inside exhaust pipes, and keeping the temperature of the exhaust gas elevated is all about maintaining supersonic gas velocity and controlling the related shock wave.

Skylor

I have to be a bit skeptical of there being any supersonic flow in the exhaust pipes. I would not be surprised, though, if some shock waves develop briefly in the actual valve orifice. Anyway, it would be interesting to do some basic calculations of average velocity, based on the mass flows and temperatures.

Back to the ceramic coating - if one made the assumption that 1) radiative heat transfer is significantly altered by the coating, and 2) radiative heat transfer is fairly prominent in reducing exhaust gas temperature, one could state that the exhaust will be hotter further downstream with the coating than without. That being said, it is a bit of a leap to pronounce that somehow power will be increased. It may indeed be the case, due to lucky modifications to the scavenging behavior, that the power is increased (the resonant length of the exhaust would be shorter, due to increased speed of sound in the hotter gas, blah, blah).

As far as exhaust back pressures in a general sense - hotter exhaust means lower viscosity, lower density but higher velocity. Is this better for scavenging? Dunno, but it could change the optimum rpm at which one gets the most benefit from it.

Bring on the dyno comparison Dan H has suggested.
 
Heat

I wonder how much cooler in degrees it will keep the engine compartment with the exhaust coated inside and out
Tim
 
Radiant heat

The heat off the exhaust system needs to be addressed as it can and will destroy components located close to the headers /tailpipes. For an experiment, turn on the surface burners of an electric range to high. They will produce roughly 1200f.. Se how long you can hold your hand close to it...

This motor in my dnyo cell, lights were turned off for the pic.... Middle pipes were 1390f. front pipe was 1410f and the rear pipe was 1425.....

Like it on not. this is what your exhaust system looks like under your cowl while you are flying...

http://www.flickr.com/photos/89759054@N07/12259560143/
 
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Has anyone here actually done a dyno run, swapped for coated pipes, and done another dyno run?

Methinks a promise of more power is a better sales pitch than "Your headers won't rust so quickly." ;)

This has been done a bunch of times both with the wrap and ceramic in the car magazines and shows HP gains. One can still question the objectivity of these publications, as they do need to keep their advertisers happy, however.

I wrapped the exhaust pipes on one of my old Pontiac GTO's from the exhaust manifolds back to about the transmission crossmember. Didn't notice any performance gains (nor was I expecting any), but the tailpipe tips were hot to the touch after that. That wrap sure moves the heat downstream.
 
Here are two articles I found when I was researching the idea. The third, another hot rod magazine test of strictly the same manifold before and after coating showed a large drop in surface temp, but IE says it can no longer be found.

http://www.hotrod.com/techarticles/engine/hrdp_0612_engine_coatings/viewall.html

http://www.carcraft.com/techarticles/high_tech_ceramic_coatings/

As for gains, all I was looking for was reduced temps under the cowling and to keep the exhaust hot to the pipe for my augmenter design. I also coated my intake tubes to keep the air colder. Didn't consider the loss in oil cooling and had to go to a larger oil cooler (2007X).

I have held a roughly 3"X 4" square coated piece of steel in my hands while the upper half was heated cherry red and had no problem holding it. Picture of similar test here from the person that did mine. http://www.cradin.com/thermal_barrier.htm

Also my neighbor has a completed coated (heads, pistons, exhaust, everything) Lycon IO-320 in his Lancair that runs very cold and has dyno'd at 218 hp at Lycon. I have held the dyno report. The best explanation for engine coating I have heard is that there are only so many BTU's in a gram of gasoline and the more you keep in the combustion chamber the more work is done.
 
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Here are two articles I found when I was researching the idea. The third, another hot rod magazine test of strictly the same manifold before and after coating showed a large drop in surface temp, but IE says it can no longer be found.

http://www.hotrod.com/techarticles/engine/hrdp_0612_engine_coatings/viewall.html

http://www.carcraft.com/techarticles/high_tech_ceramic_coatings/

As for gains, all I was looking for was reduced temps under the cowling and to keep the exhaust hot to the pipe for my augmenter design. I also coated my intake tubes to keep the air colder. Didn't consider the loss in oil cooling and had to go to a larger oil cooler (2007X).

I have held a roughly 3"X 4" square coated piece of steel in my hands while the upper half was heated cherry red and had no problem holding it. Picture of similar test here from the person that did mine. http://www.cradin.com/thermal_barrier.htm

Also my neighbor has a completed coated (heads, pistons, exhaust, everything) Lycon IO-320 in his Lancair that runs very cold and has dyno'd at 218 hp at Lycon. I have held the dyno report. The best explanation for engine coating I have heard is that there are only so many BTU's in a gram of gasoline and the more you keep in the combustion chamber the more work is done.

Why would you have a loss in oil cooling? Was it a gain in hp
Tim
 
Found an excellent article about exhaust systems for performance cars (F1). It appears coating vs HP is a bit more complicated. What counts is diameters and lengths to obtain the wanted inertial scavenging and wave scavenging. The material properties of the pipe is a part of the equation. I take this to mean that if the pipes are tuned for stainless steel (for instance), then if you coat them, you will de-tune your pipes and gain less HP. If your pipes are not tuned at all, and you coat them, then you might get lucky, or not.

http://www.formula1-dictionary.net/exhaust_road_perf.html

Assuming that an exhaust system is otherwise properly designed, equal length pipes offer some benefits that are not present with unequal length pipes. These benefits are smoother engine operation, tuning simplicity and increased low-to-mid range torque. Strangely enough, Formula 1 engine use equal length pipes, but with increased mid to high range torque.
If the pipes are not equal length, both inertial scavenging and wave (resonance) scavenging will vary among engine cylinders, often dramatically. This, in turn, causes different tuning requirements for different cylinders. These variations affect air/fuel mixtures and timing requirements, and can make it very difficult to achieve optimal tuning. Equal length pipes eliminate these exhaust-induced difficulties. "Tuning", in the context used here, does not mean installing new sparkplugs and an air filter. It means configuring a combination of mechanical components to maximum efficiency for a specific purpose and it can not be overemphasized that such tuning is the path to superior performance with a combination of parts that must work together in a complimentary manner.
In an exhaust system that is properly designed for its application, equal length pipes are generally more efficient. The lengths of both the primary and main section of pipes strongly influence the location of the torque peak(s) within the power band. In street and track performance engines with longer pipes typically produce more low-to-mid range torque than shorter pipes and it is torque that moves a car. The question is... Where in the power band do you want to maximize the torque?
Longer pipes tend to increase power below the engine?s torque peak and shorter pipes tend to increase power above the torque peak.
Large diameter pipes tend to limit low-range power and increase high range power.
Small diameter pipes tend to increase low-range power and to some degree limit high-range power.
"Balance" or "equalizer" chambers between the exhaust pipes tend to flatten the torque peak(s) and widen the power band.

Inertial scavenging and wave scavenging are different phenomena but both impact exhaust system efficiency and affect one another. These two scavenging effects are directly influenced by pipe diameter, length, shape and the thermal properties of the pipe material (stainless, mild steel, thermal coatings, ceramics etc.). When the exhaust valve opens, two things immediately happen. An energy wave, or pulse, is created from the rapidly expanding combustion gases. The wave enters the exhaust pipe traveling outward at a nominal speed of 1,400 ? 2,000 km/h (1,300 - 1,700 feet per second) (this speed varies depending on engine design, modifications, etc., and is therefore stated as a "nominal" velocity). This wave is pure energy, similar to a shock wave from an explosion. Simultaneous with the energy wave, the spent combustion gases also enter the exhaust pipe and travel outward more slowly at 150 - 300 km/h nominal (maximum power is usually made with gas velocities between 250 and 350 km/h). Since the energy wave is moving about 5 times faster than the exhaust gases, it will get where it is going faster than the gases. When the outbound energy wave encounters a lower pressure area such as a second or larger diameter section of pipe, the muffler or the ambient atmosphere, a reversion wave (a reversed or mirrored wave) is reflected back toward the exhaust valve without significant loss of velocity.
The reversion wave moves back toward the exhaust valve on a collision course with the exiting gases whereupon they pass through one another, with some energy loss and turbulence, and continue in their respective directions. What happens when that reversion wave arrives at the exhaust valve depends on whether the valve is still open or closed. This is a critical moment in the exhaust cycle because the reversion wave can be beneficial or detrimental to exhaust flow, depending upon its arrival time at the exhaust valve. If the exhaust valve is closed when the reversion wave arrives, the wave is again reflected toward the exhaust outlet and eventually dissipates its energy in this back and forth motion. If the exhaust valve is open when the wave arrives, its effect upon exhaust gas flow depends on which part of the wave is hitting the open exhaust valve. An exhaust pipe of the proper length (for a specific RPM range) will place the wave?s anti-node at the exhaust valve at the proper time for it?s lower pressure to help fill the combustion chamber with fresh incoming charge and to extract spent gases from the chamber. This is wave scavenging or "wave tuning".
 
Found an excellent article about exhaust systems for performance cars (F1). It appears coating vs HP is a bit more complicated. What counts is diameters and lengths to obtain the wanted inertial scavenging and wave scavenging. The material properties of the pipe is a part of the equation...

Yes. This is why simply making one change to a "well tuned" engine will require more tuning to optimize the "new" configuration. Simply coating/wrapping a set of headers (speaking about cars here) will almost certainly require an air/fuel ratio change and/or ignition timing. The sonic properties (i.e. tuning) of the pipe have changed due to the altered internal temperature. Race cars have different exhaust systems for different elevation race tracks. Same concept. An engine run at a high altitude track will have a different sonic wave speed than a lower altitude track.

There are practical considerations of course, but the more heat you retain in the exhaust for as long as possible, the better for engine power (if tuned for that, of course). For our engines which are not on the bleeding edge of tune, I'd opine the main benefit is the reduction in radiant heat in the engine compartment.
 
Why would you have a loss in oil cooling? Was it a gain in hp
Tim

The decrease in oil cooling I was talking about was due to coating the intake tubes, my current thinking anyway. The intake tubes run through the oil pan and being coated removes less heat from the oil.

As for HP increase. No way to know, since I did not dyno before or after. The owner of Cradin, who coated my parts, has an engine dyno room and has told me he has dyno data to show gains. I didn't follow up as radiant heat reduction was my number one goal. I think there are HP efficiency gains to be had by coating the comb chamber and pistons to extract as much work out of the thermal expansion as possible, but how much, who knows.
 
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