poncho@home

Any of you guys ever think of cooling down your exhaust.

I have an idea that I havn't yet and honestly probably never will try:

Liquid cooled exhaust. Basically an exhaust system inside a larger diameter pipe that is filled with antifreeze running through it and beeing cooled by a radiator. This isn't necessary all the way back, probably just till the h-pipe, but definately as far to the front as possible, even the headers if possible but space constraints would hinder that.

So what do you guys think? Could it work, and what do you think the power increase would be like? or am I just crazy?

CraZ-28

I'd say it's probably as usefull as muffler bearings.

That's my opinion though.

poncho@home

Why would you say that. A cooler exhasut would mean more exhaust fumes allowed to escapte through, warm gases displace more volume then cooler gases, and I think it would increase your exhaust scavenging, which in turn should increase power as well.

Astro

I think you would run into a problem with high backpressure. A cool gas moves with less velocity than a hot gas, therefore, any gains made would just be offset by increased backpressure. Just my .02

poncho@home

Interesting, you might be right. Have you ever heard of anyone trying something like this, possibly in drag racing?

camaro6spd

umm....i don't think that the weight it would add would be worth the gains....and y do they make exhaust wrap...to keep the exhaust HOT...not to cool it down. the hot air moves faster.

BigRuss

Astro's right. You want exhaust gases to be hotter, not cooler. That's why they invented exhaust wrap and high temperature coating for headers. It keeps the heat from escaping, thereby increasing the gas velocity.

Not to mention trying to cool exhaust would be problematic at best. 800-1000 degree exhaust heat would boil coolant almost instantly.

While you're at it, try hooking up a vacuum cleaner to the tail pipe... :sillylol:

poncho@home

I was under the impression that header wrap was to keep the engine compartment cooler thus resulting in cooler air/fuel mixture, = more power. Why would a hotter exhaust be beneficial? Running colder plugs, i.e. detonating at a lower temperature is beneficial. Everyone is always trying to generate as less heat as possible so to result in pinging. So far everything I've read on engines tells me that lower temperatures for everything is beneficial. Obviously we can't cool down 800-1000 degree temperature to the point were we can touch it, but if we can lower it 100 degrees would that not have an impact? and at what point does the velocity of hot gases plateau, if it does at all? If the velocity would remain constant say after 500 degrees then decreasing your exhaust temperature froms 800 to 700 would be beneficial, and besides thise temperatures are at the headers not through the exhaust, otherwise that type of heat would translate into very warm passenger compartments, so obviously the exhaust gases cool off rather quickly down their little voyage. Oh and that's also the reason that after the muffler you don't need large tailpipes. the gases are cooler thus require less displacement to move. Oh and if warmer gases, and I would imagine this applies to air as well, have a greater velocity then why is everyone building "cold air" induction systems? instead of warm air induction systems? I might be way off on this, but I just don't beleive the arguments thus far. Can someone actually explain these theories instead of just dismissing them. Oh and I am not trying to be a ball buster, just curious is all!

poncho@home

I just did a fast search and came across this

http://www.atvpartsdepot.com/heatfighterkit.html

86IROCZ

Someone told me that speed boats use this kind of thing. Is this true? It seems that they would have an abundance of cold water

1985_glue_factory

My boat has liquid cooled manifolds. The only reason they do that is to keep the temps down inside the engine compartment as it would be a catostrophic fire hazard if you had regular manifolds.

82camaro

You want the hotter exhaust, like they said above it helps the exhaust flow. You can't compare cold air induction with the exhaust. Cold air is more dense, to create more potential power. But cold air flows slower than hot less dense air(you also have to keep in mind that the difference it temps from a regular induction to cold air induction isn't that huge compared to exhaust temp changes with/without header wrap). Ram air is where you will see gains in power since the cool air is forced in. Hot air is less dense and flows faster--good for exhaust. All that matters with exhaust is flow--cooling the exhaust(making it more dense) has no effect on power potential because it's on the way out of the engine. Instead, a cooler exhaust will only slow the exhaust flow down. If that exhaust was reburned in the engine, then sure it would help power--but it isn't.
Another effect of header wrap is that the underhood temps can be lower. The best situation would be to have the whole exhaust system wrapped in header wrap. The benefits past the header would be small, but it you want to try something unique....

JRoy91RS

Not busting my ***** . Cold air moving into the engine= good, cold fuel moving into the engine = good. Cold engine compartment = good. Cold exhaust = not good. Here's why: Engines depend on a pressure differential in order to operate efficiently. The greater the differential, the more efficient the engine. Gasses and liquids naturally tend to move from an area of high pressure (generally colder and denser) to an area of low pressure (generally hotter and less dense). The greater the pressure difference is between these two areas, the quicker combustion can efficiently occur. If anything, you would want to superheat the exhaust gasses (I have tried to think of a way to do this, but it would require more energy to operate than it would produce), and supercool the incoming air and fuel (usually done with a cool can, cold air induction, etc.) in order to increase the pressure differential between the intake side and the exhaust side. Most people run cold air intake systems because it is one way to increase the pressure differential. This is also why high-rise intakes tend to produce more power than lower-profile (of course this depends on many other factors as well). So the colder the intake side of the engine, the better, and the hotter the exhaust side, the better, since it increases the pressure differential, and hence, more efficient combustion. The only reason why you would want to cool the exhaust side is if the hot exhaust were in some way adversely affecting your intake temp, and even then you don't really want to 'cool' the exhaust, but find a way to keep the heat from escaping from your headers/mufflers, etc., which would actually be making the exhaust hotter. This is why wrap/ceramic coatings work so great. They work on 2 levels. They insulate against heat escaping into your engine compartment, thereby decreasing the temperature of incoming air, and keep the exhaust gasses hotter by trapping that heat, increasing velocity.

Cooling exhaust gasses would also increase chances of turbulance, which is a different issue altogether. So to sum up, you want cold going in, and hot going out. The colder it is going in, and the hotter it is going out, the more efficiently your engine can operate, especially at higher RPM's. I should note that this is a VERY oversimplified explanation, but hopefully, you get the idea.

James

breathment

not to mention that if your running a cat. cold exhaust will render it useless, and eventual prematurley kill the cat..

but you can't compare intake temps and exhaust temps.. it is true that headres are wrapped or ceramic coated not only to keep temps down in the engine compartment, but to keep the exhaust hot so you can get a few extra ponies.. plus, what kind of radiator would you have to use to get rid of that much heat?

JRoy91RS

Not busting my ***** . Cold air moving into the engine= good, cold fuel moving into the engine = good. Cold engine compartment = good. Cold exhaust = not good. Here's why: Engines depend on a pressure differential in order to operate efficiently. The greater the differential, the more efficient the engine. Gasses and liquids naturally tend to move from an area of high pressure (generally colder and denser) to an area of low pressure (generally hotter and less dense). The greater the pressure difference is between these two areas, the quicker combustion can efficiently occur. If anything, you would want to superheat the exhaust gasses (I have tried to think of a way to do this, but it would require more energy to operate than it would produce), and supercool the incoming air and fuel (usually done with a cool can, cold air induction, etc.) in order to increase the pressure differential between the intake side and the exhaust side. Most people run cold air intake systems because it is one way to increase the pressure differential. This is also why high-rise intakes tend to produce more power than lower-profile (of course this depends on many other factors as well). So the colder the intake side of the engine, the better, and the hotter the exhaust side, the better, since it increases the pressure differential, and hence, more efficient combustion. The only reason why you would want to cool the exhaust side is if the hot exhaust were in some way adversely affecting your intake temp, and even then you don't really want to 'cool' the exhaust, but find a way to keep the heat from escaping from your headers/mufflers, etc., which would actually be making the exhaust hotter. This is why wrap/ceramic coatings work so great. They work on 2 levels. They insulate against heat escaping into your engine compartment, thereby decreasing the temperature of incoming air, and keep the exhaust gasses hotter by trapping that heat, increasing velocity.

Cooling exhaust gasses would also increase chances of turbulance, which is a different issue altogether. So to sum up, you want cold going in, and hot going out. The colder it is going in, and the hotter it is going out, the more efficiently your engine can operate, especially at higher RPM's. I should note that this is a VERY oversimplified explanation, but hopefully, you get the idea.

James

poncho@home

James,

I get the idea...I was just throwing this topic in to help this messsage board out, but I really appreciate the time and effort you put into explaining it to me rather than replying in a condescending manner.

I understand the concept of cold air induction and now I also fully understand the need for a hot exhaust. I was just hypothesizing that a cooler, thus less voluminous exhaust might be beneficial but now I see the flaw in this theory.

breathment

thats cool.. remember, there is no such thing as a stupid question, cause i know i''ve sure asked a bunch here.... we all have to learn somehow.

BigRuss

"Remember, there are no stupid questions... only stupid people." -Mr. Garrison

Patrick007

I just read everything n still think he's got a point. First off high pressure is hardly ever associated with cold n dense gasses. If you look at the equation PV = nRT ( i assume most of u know some chemistry)... u can see that if T (temp.) is increased.. pressure is directly increased. Thus, areas of high temp. are generally high in pressure, and if allowed to expand, shall become less dense. So the part above about moving from high pressure to low pressure is correct, but not the part about high pressure being cold and dense. Now, to move on, it seems to me that if you were to cool the exhaust discharge (assume no cat) its pressure and volume would in turn decrease (as can be proven by the equation above again). If the exhaust then takes up less volume, then it would seem to me that it would be able to travel through the same diameter pipe at a much higher rate of speed. Also, decreasing the temp would result in lower pressure... also known as backpressure. So again it would seem to me that backpressure would also be greatly reduced if the exhaust discharge was cooled. So.. there's my .02...n from what I know about chemistry.. this would seem to be correct.. but... feel free to prove me wrong.

Patrick DeGrosse Jr.

JPrevost

James is on the mark.
There is a theory that keeping your air injection system on full time helps heat up the headers. By injecting the fresh oxygen rich air into the headers they will react with the unburned fuel. This is a side effect and not the primary reason for the air injection system. AIR's purpose is to heat up the o2 sensor and the cat converter.
You can't really run the air injection system on an EFI car because it's an exhaust leak before the o2 sensor. You'll get a high reading of oxygen and the ecm will think lean condition and dump in gops of fuel. So....running a carb, try it out, running with EFI, out of luck.

Astro

Pat,

Good use of chemistry. But think of it this way, all gases are fluids, and as all fluids decrease in temp, they become more viscous (resistant to flow). Therefore cooling a gas would only make it flow slower, and the build up of gas in the exhaust system would cause much more backpressure than high temp, high pressure, but much faster moving gases.

poncho@home

I am really enjoying this exchange of ideas, but I have to disagree with yo Astro that gases are fluids....fluids and gases are two seperate states of various elements.

Patrick thanks for the support, but my knowledge of chemistry is to rudementry to either support or acknowledge the fault in this idea. I am just glad the debate continues.

Astro

actually poncho, liquids and gases are both considered to be fluids. It is a broad scientific definition that encompasses all substances that flow.

Patrick007

While gasses and liquids can both be deemed 'fluids'... gasses and liquids are hardly alike. And what u said about fluids becoming more viscous does not really pertain to gasses. The reason why some liquids (not all) become more viscous when cooled is because the molecules actually slow down, and the more you cool the liquid, the more it approaches the solid state, thus becoming more viscous. In a gas however, as the gas is cooled... while the molecules will slow down just as a liquid... its 'viscosity' will not change quite like a liquid such as oil will do. The gas only decreases in volume and in pressure.... so i can't see a cold gas flowing slower than a hot gas.

Patrick DeGrosse Jr.

JRoy91RS

Hey, poncho, I didn't mean to imply you were asking a stoopid question at all. I have learned so much from these boards myself. In fact, I applaud you for putting your nuts on the line and trying to come up with an idea. I wasn't trying to shoot it down or anything.




Ahh, yes. but as a gas increases its velocity, its pressure also decreases to a degree greater than that to which heating it has any effect (at least with respect to a combustion engine). If you were to measure the pressure differences on the intake side and the exhaust side, you would find that they are huge!! The reason why is that the air moving in is moving in much slower than that which is moving out; and good thing, because if it weren't, then you would have some serious detonation ! Another reason why high pressure is associated with cool, dense air, is because of the proximity of the molecules in the gas. The molecules on the intake side are so close together (because they are moving so slow), while the molecules on the intake side are very far apart (because they are moving so quickly). So far apart, in fact, that it doesn't make much difference how hot they are. Another example used to illustrate the cold:high pressure:: hot: low pressure analogy is the weather. If you look at the weather report, you'll see that high pressure systems are associated with cold, dense air. I'm sorry that this is so convoluted, but I'm doing the best I can without throwing a lot of calculus into the explanation. I could split hairs and talk about the difference between a pressure 'differential' and a pressure 'difference' but that would also involve some hairy calculus. I hope that this helps!

James

Astro

Actually Patrick,

A cold gas has much less kinetic energy than a hot gas, proven in many experiments and therefore not debateable. Since kinetic energy (KE) is attained by:

KE = 0.5*m*v*v

where m is the mass of the gas, same when hot or cold

and v is the velocity.

So if KE is higher for a hot gas, then velocity must be higher, as 0.5 and mass are both constants.

Therefore a cooler exhaust gas temp would be more detrimental to max power, but the setup for such a cooler could look unique on a show car.

Also, on your PV=nRT, this usually only applies to closed systems. Since the exhaust is open at the end, the increase in pressure will help push the gas out of the exhaust system.

JRoy91RS

Astro, you summed up my points eloquently with the good old KE = mv^2. Exactly what I was getting at. KE translates directly to temperature and proximity of the molecules.

89V6FBIRD

Who would've thought taking AP Chemistry would come in handy in exhaust cooling.... :lala:

poncho@home

I should've paid attention in chemistry class ....thanks guys, great debate with actual science backing it. These are the type of dialogues we should be having on message boards, not the usual cyberjunk that I spend most time sifting through to find something of interest to read. As you tell by my post #s I don't often engage myself in the posts here, but I have been lurking for a couple of years now.

Patrick007

Not a good example at all. The reason areas of high pressure (as far as weather is concerend) are associated with the colder air is because the cold air is actually falling through the atmosphere... actually pressing harder upon the earth (Earth Science 101 baby)... this in no way relates to what we're talking about.

BTW I've also taken physics n calculus 1 and 2 so feel free to go into the calculus.

In this situation, the equation still holds true. One can examine one specific section of the exhaust system, and determine the pressure, temp., and volume of that section, and even if it IS actually open to the environment, the equation can still be used to prove TRENDS of gasses. Such as the trend that as T is increased, P and V will also increase.



Only point so far that I somewhat agree with. Yes KE = 1/2 MV^2 and yes a hot gas's molecules will travel faster, but you must understand that these molecules are still moving in all directions. Thus this faster moving gas (hot exhaust) will have molecules that are colliding with the walls at a much higher rate of speed, therefore creating more pressure (backpressure). Yet again this hot gas will also want to expand ( needs more volume)... again more pressure. So the question now is which is better. Does one want their exhaust to have a high velocity but with very high pressure..... or a lower velocity but with greatly reduced backpressure.

BTW... anyone ever heard of this being tested before? I do alot of kart racing too with the trust briggs.. i'm contemplating testing this theory on a kart engine with an extended header.

Patrick DeGrosse Jr.

TS b4c

A point that was not discussed much here is scavenging. I don't know all the physics so bear with me. Here goes... As the valve opens and the piston pushes the gas out it is expanding very rapidly and moving at a high velocity. The exhaust gas charge will actually create a vacuum behind it because of the speed at which it is moving and the loss off pressure as it cools. To get a benefit from this you want the exhausts as hot as possible as it leaves the header/ manifold and to let it cool farther down the pipe. This effect will actually help pull all the exhaust out of the cylinder plus provide a lower pressure so the next piston does not have to work as hard to push the exhaust out. Thus less power needed to push exhaust = more power to push wheels.


Now for the cold air theory. Cold air is denser the hot air (not rocket science). Cold air does create more atmospheric pressure because it is denser so all the weight of the air above pushes down and creates more pressure at the surface, enough earth science. Cold air helps car get more power by having more oxygen in the in the same size of area allowing the engine to burn more fuel. Cold air being denser also slightly raises the compression in the cylinder giving the engine more power. Colder air also reduces the risk of detonation. A cold air intake kit is a good cost effective way to increase Hp with minimal work.


Feal free to correct me on anything. THis is my understanding off how things work... plus hangovers never help while trying to have clear thoughts.

FLYNLOW92rs

iTrader: (53)

Ok, i recently did this in AP Chemistry, so my memory is kinda good about the subject, I have shown the following graph below.

Now, Temperature is a measure of Kinetic Energy so in a cold gas has less Kinetic energy then a hot gas, look at the graph below.

Here is a direct quote from my text book
<p>
what it means it that when preesure if applied to the exhaust pipes(system) the gases will look for the area with the lowest pressure(outside through the tips), therefore when the pressure is lowered(cooling exhaust) the speed at which the gases will look for a lower pressure will decrease thereby actually slowing it down. High pressure can olny exsist with high temperatures.
<p>
Ok well there is my .02, I have more formula's and graphs if somebody would like me to post more to prove my theory.

TexasLT1

holy crap, I never dreamed that AP Chemistry would actually come in handy and be put to use! just wanted to say good job to everyone who used science and math to back up what they were saying instead of the "its right because I said it is and you cant change my mind" mentality. its more discussions like this that we need on this board

JPrevost

Cold air means you can add more fuel (to keep it stoich or similar AFR). This is the opposite of what the EGR system does. The more fuel you have in the cylinder the more likely it is to detonate. This is why tuners feel so strongly about burning their own eproms!
EGR will let exhaust gas (almost no oxygen) mix with the intake charge to cool down the combustion chamber. This enables you to run more timing for better gas milage. The reason you can run more timing with EGR is because it's less likely to detonate and by now you should know that a lean AFR can run with more timing and a richer condition needs less. It's all about tuning and a nice balance, you can't look at one thing and not the other when it isn't JUST air going into the engine, it's got fuel too.
As for the exhaust hot or cold, hotter the better. Yes header wrap cools down the engine compartment but it also helps free up a little more power. Don't forget, heat is a sign of energy loss. This makes me think that if you ran in open loop or have a carb, keep the air injection system and have it pump all the time to keep those headers hot (good ol' Smokey Yunik's theory).