Ok, here we go. . .

all correct, however what you are forgetting is that you are not changing the pressure ratio of the engine, you are just changing the temperature range over which the cycle is operating, colder (say 70*F) air drawn in from in front of the grill at 1atm(lets just assume this for the time being) is at the same pressure as hotter(lets say 150-200*F) air drawn in from under to hood, the pressure P1 doesnt change, so when the volume decreases from V1 to V2 the pressure increase from P1 to P2 is still going to leave you with the same ratio as it did before.

ok I think we all agree on this part already.


yup I think we can work this out

compression ratio is absolute, maybe not exactly the same cylinder to cylinder, or engine to engine, but it is a simple mathematical forumla, volume at bdc (bottom dead center) divided by volume at tdc(top dead center)
Vbdc
Vtdc

bolt ons mods cannot change this, it is simply a measure of how much (air water w/e) will fit into the space inside the cylinder between the head and the top of the cylinder.

1. I already addressed the EGR reference, I never said that I had one in my truck, or that any 1st gen durango had one, just used it as an example.
2. ICE do NOT operate at stoichiometric numbers, they are for ideal operation where the operator has 100% control over EVERY SINGLE DETAIL of the operation, this is NEVER possible for you or I to achieve, so ICE are designed to be operated with what is known as excess air, the calculations are made to determine what the perfect stoichiometric numbers would be (usually using MASS as the basis for these equations) and then in order to ensure complete (as complete as possible, that is) combustion they run at a percentage of EXCESS AIR, this is so that all the fuel will burn(hopefully) and no pollutants are produced (ideally, of course, in reality some are still created)
3. the computer in the truck knows where stoichiometric perfection should sit, and it also has the amount of excess air that the engine was designed to operate at programed into it. Stoichiometric numbers would be the best place to operate the engine of course, but is unrealistic under real world conditions.
4. And more fuel equals more heat added to the cycle which equates to more work produced, work is proportional to power.

yes the CAI is going to cause colder air to be drawn into the intake and the computer will pick up on this and increase the fuel supply in order to maintain the molar and mass ratios (if you really want to understand these let me know and ill try to explain), thereby producing more power (it will feel this way at the very least).

Yes I agree that you will notice the loss of power when operating under extreme conditions and extreme loads, I never argued that point, I simply said that for normal driving if you pull in warmer air you wont notice much (if any) of a difference in power and will probably have an increase in mpgs, how many people do you know complain about a loss of power in the summer versus the winter (and im NOT referring to people with very well built up engines, or people referring to A/C draw on the engine)

this article appears to me to be discussing mostly the changes based on pressure differences caused by altitude changes . . .





ok so here we go now, into the thermodynamics of the modern Interal Combustion Engine (ICE)

lets start with some basics, that many of of us should already know. The engines in these trucks work on a 4 stroke principle governed by what is known as the Otto Cycle(also known as the gas power cycle, diesels operate on a similar slightly different cycle, im not getting into that here). This cycle consists of 4 strokes, intake, compression, power (combustion), and exhaust. Each of these portions are assigned a different state number based on where the cylinder is on that stroke. These state numbers are what you will see later on following variables such as V(volume) P (pressure) ect.


State 1 is when the cylinder is at Bottom dead center (BDC from here on) of the intake stroke
State 2 is when the cylinder is at Top Dead Center (TDC from here on) between the compression and power strokes
State 3 is after combustion, which for the sake of this discussion, and to simplify things a little bit is assumed to be an instantaneous combustion of all fuel in the cylinder, and it occurs at TDC bwtn compression and power strokes(in reality it occurs during the first small portion of the power stroke, but again this is simplified for you and me)
State 4 is when the cylinder is at BDC before starting the exhaust stroke.


We simplify the process for anlysis as follows
process 1 is compression
process 2 is constant volume heat addition (combustion)(yes I am aware this is not true in real world applications, but for the sake of this discussion approximates it closely enough)
process 3 is expansion (power stroke)
process 4 is constant volume heat removal (exhaust stroke in reality)


the actual pressure-volume graph


the P-V graph we are looking at in this ideal situation.


the T-S diagram which is where I believe you will see what is going on the best.

As you can see when air is drawn into the cylinder with lower entropy (S1) the work (length of the process line representing compression stroke, line 1-2) is lower, as the entropy of the intake fluid drops so does the length of this line. In order for this make sense we need to understand that at a given constant pressure (say 1 atm) entropy and temperature are proportional, as one goes up so does the other, and that the pressure lines (2-3 and 4-1) converge as they go to 0 and diverge as they approach infinity. Now, we move the intake temperature down, we also move the peak temperature down some, it just doesnt move as far as the intake temperature because of the addition of extra fuel, so the line representing the work done by the engine (line 3-4) remains relatively constant. The Total net work output of the cycle is the difference in the length of these lines, so if you make one line shorter while not affecting the length of the otherone what happens??? if you said that the net work output increase you are correct.


Now that we see why drawing in colder air will increase the WORK output of an engine we need to know what that has to do with power output, its simple power is equal to WORK times Speed OR:

Power = Work X Velocity.
(velocity in this case is angular velocity or RPMS)

now what else changes when the temperature drops you ask? Simple, the mass of the air, which also means that the Amount (in moles) of air will change (mole is a measure of how many molecules of a substance are present in a certain volume). This increase in molecules is what the computer calculates in order to determine how much fuel must be added to the cylinder in order to get the same (approximately the same anyway) combustion products, which would ideally consist of nothing more than water, carbon dioxide and Nitrogen, however with the need to operate with excess air there will also be unburned Oxygen in the exhaust too.

Ok I think that covers it but if not ask away im not putting my books away yet . . .


anyone who wants to read more take a look at chapter 9 sections 1 and 2 of Michael J Moran and Howard N Shapiro's Fundamentals of Engineering Thermodynamics.

 

Uh...wow....well uh......how bout those Mets?

 

Sharps<---- You were correct on the EGR, I miss read your post.



Incorrect. A Camshaft or Port And Polished heads will increase the constricted flow into the cylinder by opening the intake times longer of a wider mass intake, therefore creating more air in the cylinder, if more air is in the cylinder then more fuel will then be added to ensure the correct mixture. Secondly, any type of boosting system will also add more compression. It's like getting a cylinder with a small opening at the head and pulling down on the base, there is a constriction (Vacuum) inside the cylinder thus the entire cylinder is not completely filled with the normal atmospheric pressure because there is an actual time that it is open.

Now take the same cylinder and open the head all the way (no constriction), pull down on the base, with in the same opening timing, and you WILL get more air into that cylinder because there will be no vacuum effect. The more air you get into that cylinder in that short opened head/valve the more compression will be made PERIOD! Now you have more air shoved into that cylinder (because you changed the flow from OEM) the PCM injects more fuel and more power is made on compression stroke.

Now, on paper there are no variables like head constrictions, time the valve is open, heat from surrounding cylinder, blah blah blah. But when you take that paper drawings to the actual building of the motor you get a difference in ACTUAL numbers because of the variables. What I'm talking about is positive/negative pressure ratios because of the intake, and from the OEM setup you will gain compression. Manufactures Compression Ratio is on paper and includes many of variables like those I'm talking about, but if you change the system you will change the numbers and those equations are now out the door.

Now you add that along with cooler air intake, positive pressure intake (like that on a ram air system), you will also get denser air into the cylinder thus giving the engine a leaner than normal mixture. Then the PCM regulates more slightly more fuel to get the mixture correct.

Just because you have more fuel (rich burn) you will NOT get any more power out of it! You will not get anymore power out of a lean burning engine as well. The perfect mixture will give you the most power and best performance. Any old mechanic that has tuned in a carbonator by ear can tell you that. It's basic as the wind. All you need is just enough air to burn the fuel! Any more air is not going to burn more fuel because there is no fuel left to burn (lean burn), = jack squat, any excess fuel with not enough air to burn it wont fully burn and goes out the exhaust (rich burn)= jack squat. Therefore, just because you add fuel you do not get more power out of it, so get that idea out of your head.



Nobody complains on warm days because they are actually getting better fuel mileage, not to mention better gas. But they do complain when they start to tow or cause heat buildup. Everyone out there loves the power of those increase cool days, at least I know I do, and I can defiantly feel the difference. Secondly, have you ever followed behind a motor home on a hot day towing your own load and they spill some water out of their holding tank on to the ground. And as this happens the water meets the wind/heat/road and makes a slight mist? Well I tell you what, with a ram air intake you watch that evaporation of heat in a dry climate just give you what feels like 50 extra horses and cools you water temp EVERY quickly! In fact, that probably would increase the oxygen molecules in the cylinder?......Hmmmmmm……LOL…….A different day maybe?


There are many extras you get when everything is running cooler and more efficient.

 

ok hydra, i see whats going on here, we are talking about different volumes here, you are talking about the volume of air at 1 ATM (for NA engines) that is pulled into the cylinder, and i am talking about the absolute volume of the cylinder, (yes these two numbers are different, as hydra illustrated above, the air flowing in at ATM pressure will fill the entire cylinder, however at a pressure slightly LOWER than ATM) the published compression ratios are the design ratios, or the absolute volume of the cylinders, while the numbers YOU are talking about can vary based on the flow velocity of the air. However manufacturers publish the highest compression ratio they have on the engine (which is the design spec number in most cases) because higher compression ratio = higher efficiency.

also a boosting system changes the pressure ratio of the engine, which will change the volume of air in the engine if that air were at 1 ATM, however since the boost is putting air in at HIGHER than 1 ATM it fits into the same volume as the smaller mass of air at lower pressure.

also if you re-read my other threads i explained why more gas = more power, because the more gas you BURN COMPLETELY the more power is produced, i NEVER said that running rich would produce more power. However if you look at the thermodynamic study of reacting mixtures (the most common of which is combustion) you will see that there is not a single combustion engine (turbine, ICE, boiler ect) which operates at perfect theoretical values, operating with an excess of air allows for a more thorough combustion, will not produce more or less power because of this, but this is the way that combustion engines operate simply because the mix cannot be created to be 100% equal. Newer technologies in ICE have decreased the amount of excess air needed for combustion by producing a better mix of air/fuel, however the excess is still required to make sure you don’t have small volumes of unburnt gas in the cylinder (or combustion chamber) after the combustion process has been completed. If the air and the fuel mixed exactly perfect all the time you would operate at exact theoretic (stoichiometric) values but in order to accommodate real world operating conditions combustion engines operate with excess air.

and on the last part, yes people like you and I will notice the power difference, but ask any random idiot (ok normal person) on the street if their car has more power in the winter than the summer and they will look at you funny, 90%(ok, maybe its not that high, but still the majority) of the population who use their cars as nothing more than appliances will NEVER NOTICE this increase because it is so small and they dont tow or use their vehicle in situations where they would need the full potential of the engine.

 

Ladies, please! Can we get back to helping the OP with his problem rather than arguing over all that math BS? lmao I mean come on.

 

we gave the OP information before we started into this and he came back and said it hasnt happened again and will update us if it does

 

Hell ya Sharps!

devin<---- What you have to understand is these type informative discussions open up a lot of new ideas that actually help the members.
This is a misconception the sell to the un-informed buyer. They are getting their numbers legally, but not the actual numbers across the board.

What you said multiple times was if you increase fuel you get more power, that concept is incorrect.....just saying.

What I am simply stating is a clarified proven fact, not a misconception....No offence.

That' only because they aren't looking at the whole picture. It's freaking cold outside and they are trying to get where they are going, they could care less how their truck is running as long as it is running half way correct and get them where they are going.


But again, it doen't matter, it is clear we are talking about 2 different things.


Let me tell you this, spend one week building a motor with me and you will see that text book go flying out the window and the fact of reality coming into play. This is why experience rules, even though us un-educated people can still stand up with the tech gurus.......LMAO

 

yes hydra i said multiple time that more fuel equates to more power, but i also explained that it was more fuel burned = more power and that it was not as simple as throwing more fuel into the cylinder, because i believe i said something about more air being pulled into the cylinder and that bc of that increase in air mass there would be more fuel used.

how is higher compression ratio = higher efficiency a misconception???? the math and the testing that has been done supports it, no misconception there, its simply facts, most people dont know why, but they do know that higher compression = better.

I may not have as much experience as you do, but im probably one of the youngest people alive who can tune a carb by ear (granted it has been a while since iv had to do that)

 

Gentlemen,

Thank you BOTH for a great thread! There is a huge wealth of information here, and I for one enjoyed digesting it. Way back when I got my B.S. in Aerospace Engineering and this thread stirred up some of those long lost (or maybe pickled ?) brain cells.

Bob

 

What I was referring to was the statements "if you add fuel you get more power", and in that is a misconception. However you caught on to what I was talking about, but for the members that don't know, well I spelled it out.

You have a lot of other experience in other fields than I do, and in the art of mechanics things get forgot about or "overlooked". School teaches the basic physics, but experience in seeing many systems really helps out.

It was like when we were talking about the rear brake shoes, the "rocking motion for adjustments", you had more info and was right, and I was still stuck in old mechanicing......LOL