Energy cannot be created or destroyed, only transformed. When fuel is burned, the chemical energy it contains is transformed into thermal energy. When it's burned inside an engine with the piston near TDC, the expansion of the burned fuel pushes the piston, transforming the energy from thermal into kinetic (it's actually a little more complicated; depending on load, timing, and speed there's a mix of potential and kinetic energy, but for our purposes at the moment we can think of it all as kinetic). The transformation from thermal to kinetic isn't perfect, because some of the heat is absorbed by engine parts that cannot move and therfore cannot convert thermal energy into kinetic. The cylinder walls and cylinder head, for example. Heat that escapes into the engine block and cylinder head is eventually carried off by the cooling system and shed into the atmosphere, having done no useful work for us. Likewise, there's heat left over in the burnt fuel/air mix and it is ejected via the exhaust system, also having done no work for us unless we've got a turbocharger in the line.

Remember, as the heat of a gas increases, so does its (unconstrained) volume or its (constrained) pressure. Anything that increases combustion chamber pressure — increased compression, forcing more fuel/air mix into the cylinder, advancing the ignition timing, colder=denser air charge, etc. — means more heat when combustion occurs, which means more push on the piston. It also means that for any given percentage of heat lost without transformation into kinetic energy, there'll be a higher absolute amount of such heat loss. And of course one must consider the limits (raise cylinder pressure too high, and you'll get detonation).

But it's not just a simple matter of crankin' up the heat in the intake tract. Consider EGR, which admits very hot exhaust into the intake tract. Its effect is to lower peak combustion chamber temperatures; the exhaust is mostly inert/noncombustible, and so despite the higher intake charge temperature, there's less fuel in the charge, therefore a "smaller bang", less heat = less pressure in the combustion chamber, and therefore less production of NOx and less tendency to ping. Ping abatement is good, NOx abatement is good, but the reduction in engine performance is...not so good. If you will think about this example for a moment, you will probably get some insight into why the fuel-heating idea is being looked upon dimly.
Yep. The higher the temperature differential, the greater the heat loss. What's more, the cooler the coolant surrounding the combustion chamber, the greater the quenchout effect (wherein fuel on/near the surfaces does not burn, or does not burn completely). This explains the lower emissions with a hotter thermostat, and the upshot is pretty obvious: Burn more of the fuel, exhaust is cleaner, and bigger push on the piston.

But, there are conflicting forces at work. Increasing the engine temperature means more complete fuel burn, but also tends to mean a hotter, less-dense intake air charge, which means less cylinder pressure, which means a "smaller bang" and less piston pushing power. So you want to run the engine hot, the intake air and fuel cold, and watch out for pinging. Take a look at how most all vehicles are configured from the factory nowtimes: Hot thermostat, cold air intake, and undercar/underhood fuel line, filter, rail, & injectors constructed, positioned, & mounted so as to minimise fuel heat absorption. It's also worth a moment's consideration that the biggest (almost said "hottest") thing these days in propane motor fuel is liquid propane injection. Colder, denser fuel = bigger bang = more cylinder push.

Water/methanol injection, depending on proportion and control, can cool down the combustion chamber and/or increase the cylinder pressure.
Well...efficiency, yeah, we are. It just refers to how much of the fuel's chemical energy we can transform into kinetic energy. Higher efficiency is better than lower efficiency. We can choose to use the kinetic energy in such a way as to maximise fuel economy or in such a way as to maximize acceleration and speed, or something in between those two extremes.
Generally lower, because you want to extract as much heat energy from the exhaust inside the engine as possible, because that's where it can do work for us. Heat thrown out the tailpipe is lost and gone forever without doing any work for us. Note that cam and ignition timing affects EGT: If the spark occurs late or the exhaust valve opens early, the fuel/air mix will still be burning (or at least will still be hotter than with an earlier spark or a later valve opening) when it is ejected into the exhaust system. Retarded timing is a well-known cause of engine overheating; the still-burning fuel/air mix acts like a torch on the cylinder head via the exhaust ports, which heats up the coolant in a big hurry. If the timing is very retarded, and you open the hood at night, you might get to see the exhaust manifold glowing.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Thanks. That was a very well thought out discussion. Underlying theory such as this gives you a deeper understanding of why we do what we do, and helps you think through any future projects. I really think the more basic you can be in your understanding of underlying principals the more intelligent your process can be.

So is there an exterior engine color that is inherently more efficient? Is there a color that broadcasts less heat? I have heard it said that black is the best color for this reason, but the source was not verified at the time. I bought my 360 that went to my since sold '70 Dart that he painted it black for this reason. Of course I had to paint it back hemi orange.

I guess the higher thermostat is going back in, and I am dealing with detonation another way if it comes back. Maybe a number 7 plug is next in line. And of course the water injection thing is hanging out there.

Sam

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You're welcome. I'druther we'd had it while standing around under the hood of your car!
That's an interesting question, and one I played with a long time ago as a science fair project, using air-cooled Tecumseh engines and a borrowed IR thermometer. Tested black, white, silver, and red. No significant difference in the temp of the cylinder head, blower shroud, or ignition module (under the blower shroud). I don't think paint colour exerts a significant influence on radiant heat transfer through such things as the engine block. Of course, it's a different question if you're trying to figure out what to paint the radiator with. That's a primary heat transfer junction, and you want as little interference between the metal and the air, so from that standpoint "no paint at all" is best, but then you've got corrosion issues, so they make a special radiator paint that goes on thinly and interferes minimally with heat transfer.

The other side of that coin is the thick ceramic coatings that can be applied to exhaust manifolds/headers and headpipes to keep the heat within the system rather than letting it heat up the engine bay (which, remember, heats up the intake air and lowers the charge density making a smaller bang in the combustion chamber and less piston pushing power).

But no significant cooling takes place via direct air-to-engine-block or air-to-cylinder-head contact, so paint the engine and its tinware whatever colour you want.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Black is, in theory, a more efficient radiator as well as absorber of heat. The effect on engine performance, however, is miniscule, probably unmeasurable.

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David Kight
'62 Valiant Signet, White
'98 Dodge Dakota
'06 Jeep Liberty

Growing older is unavoidable but growing up is strictly optional.

Most heat transfer out of the engine is through convection in the cooling system.

If you want it to get rid of heat through radiation, you want a surface with high emissivity / low reflectance to infrared. Polished metals usually have low emissivities, rough surfaces tend to be higher. Color makes some difference, but some black paints and coatings are very reflective in the infrared band. Thick paints can act as insulators. The best way to tell is to have it tested. Paint type and surface condition is more important than color in radiant heat transfer.

Convection is another matter, more dependent on fluid flow characteristics of the surfaces, geometry, and the fluids involved.

Be careful with IR "thermometers" and the Raytech-type guns, which have a laser pointer and a digital readout. They can be good tools when used properly, or they can mislead you terribly. They are best used for comparing numbers from the same spot from the same direction. Don't count on the number you get actually being the temperature unless the device has adjustments for the exact emissivity of the surface and the reflected energy in that particular situation, and is calibrated. They're really not good for finding hot spots or heat patterns.

Thermal imagers are much better. Just more expensive to get!



By the way, this engine has a faded red/orang engine paint on the block, rusty cast iron finish on the exhaust manifold.

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"When you find a big kettle of crazy, it's best not to stir it." - Pointy-haired Boss

1964 Valiant V200, 225/Pushbutton 904
BBD, CAI, HEI, LBP, AC, AM/FM/USB, EIEIO

Do you agree that the goal is to retain heat, and not let it radiate? Your comments were interesting, but how would use this, once you decided what the goal is, which I am not at all sure of at this point.

Sam

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Are you wondering about encapsulating the engine in some kind of coating that would keep the heat from radiating off the engine...? I don't think this would be a beneficial idea; seems to me it would just throw more load on the cooling system without materially increasing combustion chamber temperatures.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

If you want your engine hotter a hotter thermostat will do it. I would not do anything to limit the whole systems ability to get rid of heat when it needs to. No matter how hot a thermostat, it will open all the way at some point and not limit the cooling ability. It will be counter productive to your detonation problem, if you have one. You might look at checking your charge temp right before the throttle body, it might be much hotter than one would think. This, and the increased intake pressure, is why it is usually better to run turbo engine cooler. They are generally pushing it with pump gas. Most all will have a heat soak problem if run full out for more than a minute or so, even with a decent intercooler. A gasoline turbo car engine is usually setup for short bursts, not constant pulling like a diesel turbo.

For mileage and emissions, hot is the way to run. Something like an adjustable thermostat for the coolant would be nice. Then you could run it hot or cool depending on your needs at the time. I have thought about some sort of thermostat bypass with a simple ball valve but never tried it. My experience with street turbos is that you could never get it to run below 160 anyway, unless it is freezing out. So opening a valve in normal weather would just get it in the 160+ range. Reverse cooling would be nice too. A cool head to help with detonation and a hotter block to get more out of the burn.

Remember that if you're running a turbo, you're extracting more energy from the heat of combustion anyway. It would probably be beneficial to wrap the headers or exhaust manifold to retain more heat there but trying to retain more heat within the engine block itself is risky at best. You have to balance thermal efficiency with the mechanical limits of the metals that make of the moving parts.

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David Kight
'62 Valiant Signet, White
'98 Dodge Dakota
'06 Jeep Liberty

Growing older is unavoidable but growing up is strictly optional.

It's just a question, not a theory. I don't know what is best. This kind of discussion can be very educational in a basic kind of way. I have the exhaust wrapped already. Nasty stuff, and I hated to cover the pretty jet coating I had done to it. I covered the turbo to protect the plastic hood, but maybe keeping the heat within the body of the turbo is ultimately useful as well.

I was wondering about some sort of adjustable opening in front of the radiator as the big trucks have. I was thinking about one you could work with a choke pull in some way. This would involve alot of user attention and modulation, and would have the potential of getting too hot if you didn;t pay attention.

Since the car gets considerably worse mileage on the short drive to work, it might be useful to cover the radiator opening for a few minutes early on just to get it to heat up faster. None of this is earth shaking, just kind of idle ruminations.

Sam

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The thermostat and elec fan help your engine warm up more quickly, but ultimately there is a lot of metal there to heat up (block, head...), which is part of the reason our older cars heat up more slowly than newer ones. Covering radiator might help, but it probably isn't seeing much coolant flow anyway (thermostat).

The reason for better gas mileage in higher outside temp is, I believe, just that you have hotter (less dense) air coming into the engine. and so less fuel is burned. You get better mileage, but lower HP. Same reason you get better MPG at high altitude.

Lou

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Home of Slant6-powered fun machines since 1988

I have ruined headers by wrapping them. It seemed like such a good idea twenty some years ago, but at the cost of the headers not worth it to me. At least keep the wrap a couple of inches away from any of the welds to avoid cracking them.

I would not wrap a turbine housing at all. The turbos bearings need all the help they can get staying cool. It will raise the temp of the housing but not make any measurable difference to the temp or pressure of the exhaust gas. There is so much volume and density of gas flowing thru there, especially under boost. It is not uncommon to see 40+ psi in the exhaust when the boost is at 15 psi or more. That is allot of hot gas. Metal heat shields seem the best thing for protecting nearby parts or paint from the turbines heat.

A metal heat shield is indeed what I have around the turbo. It is pretty ugly, as it is home made, and pop rivited together, but it is exactly where I want it, and the shape I need it to be. I was planning on building a vent to the outside to take some of the heat away from the turbo area to under the fender and outside. Do you think getting the turbo heat outside and away is a good idea, or is this working against the turbo principal?

Sam

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I think I agree with Another Six that the residence time of gases in the turbine housing is pretty short, and your loss will be small by venting some of that heat away from the turbo. Your bearings will thank you. Then again, your heat shield is not contacting the turbo housing, so it may not be keeping that much heat in. They are built to be hot, of course.

These are educated guesses, nothing more...

Lou

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Home of Slant6-powered fun machines since 1988

H'mmm. That was definitely not my experience driving cars at altitude of 5,500 feet and driving those same cars at sea level. Engine efficiency drops due to the lower charge density, meaning you have to boot the accelerator harder to attain any given level of acceleration or maintain any given speed. Fuel economy was definitely lower at altitude than at sea level, and it wasn't just down to carburetor jetting, since two of the cars in question were computerised EFI from the factory.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.