CAI indepth.....

[Skip_1074]

I wanted to post on this topic from the minute that I saw it, but haven't been able to actually get on a computer to do it, so here it goes which is actually better for me. I hope that I have enough understanding to help, but we'll see. Sorry if I chopped something out of your posts that was important, but I was just trying to get the points/details.

Originally Posted by hampsterzone

Well, a very good friend who is a mechanic of 25 yrs, gave me the low down. CAI's are the best for adding horsepower. The Gotts mod is cheap and effective but not as much as CAI. Moving the MAF sensor doesn't cause lean codes. It reads air flow no matter where it is. Lean codes come from custom exausts not CAI. Low back pressure cause the lean codes.

Which makes sense cause I never had a lean code with my edge and CAI alone.

But when I did headers and true dual exhaust I saw lean codes on bank #1 and bank #2.

While I don't mean to discredit your friend, I would like to know what he is basing his information off of. I've been studying, working on, mod-ing, planning vehicles for over 10 years now (import cars and trucks to domestic gas and diesels) and it just seems a little different from the norm from my research. I admit my lack of understanding is in the electronic aspect of engines and how some of the sensors play a role, but

I think Longshot addresses the movement of the MAF sensor and/or its coexistence with a CAI as well as the lean environment in the next quote very nicely. I will expand more in a few.

You never experienced a lean code with a CAI and the Edge because even though the Edge wasn't calibrated specifically for the CAI that you were using, it had altered your fuel trim already thus providing more fuel to the engine. That being the said, without actually knowing the strategies, or understanding them for that matter, that Edge uses (and many other factors such as tune used, octane used, CAI brand and tube diameter at MAF sensor in comparison to stock), I believe that your the Edge kept your A/F ratio with CAI somewhere around the what the stock programming had.

I will also try to explain the exhaust setup's existence in a few. I'm trying to keep to one point at a time.

Originally Posted by Longshot270

The commercial "cold" air intakes use a larger diameter pipe than the stock sensor housing.
This is a picture that demonstrates what a cross section would look like. The blue area is what the truck calculates for and the red area is what is not calculated because of an aftermarket intake that is larger than the stock housing.


With the larger diameter, the air will flow at a different speed. If you were to bring in 60 grams/sec of air it will flow faster in the narrower tube. Higher air speed, lower wire temperature.
On a stock truck the sensor is calibrated for the stock fluid area (blue). Any result you get from the MAF sensor can be calculated into an accurate physical volume. If you increase the diameter, you change the air speed, you change the reading and in doing so, you change how much air an electrical value represents. This is where custom tunes come in and we've got plenty of threads about that.

So the sparknote version:
Yes, the MAF sensor will read airflow no matter where on the intake track it is located, but that does not mean the reading will be accurate.
When you increase the diameter of the pipe the air does not need to move as fast to move the same volume. The slower air velocity will read on the sensor as the wire being slightly warmer, making the resistance slightly different. When the value is different the truck fuels different.

As I stated, I think this is a very good explanation. I honestly can't explain it better, but can only maybe elaborate upon it. I know that it is more technical then what I am about to explain. My mind thinks in numbers, so please forgive me.

If you have a two hoses and pretend that the small one is stock and the larger is a CAI...lets say a 3" (7.07 square inch cross section) and 4" (12.57 square inch cross section)...and a sensor that is 1" by 1" (1 square inch) that extends into them. The sensor is designed to take a sample from 14.14% of the 3" hose and that is needed to provided accurate flow calculations, but when placed in the 4" hose, it only takes a sample from 7.95%. That means only 56.22% of the required sample is being provided for the calculations.

If this doesn't make sense, let me know, but I hope that it helps better explain the situation. I have a post from another forum that is about 880 words that really breaks it down if anyone wants to read it.

Originally Posted by hampsterzone

Any thoughts regarding exhaust causing leaner conditions? I would love to hear your opinion. (anyone's for that matter).

Okay, on the the exhaust and addition to an Edge and CAI. "A chain is only as strong as it's weakest link." This works two ways on an engine:

1. You can only suck in as much air as the exhaust system can expel.
2. You can only expel as much air as the intake can suck in.

My understanding is the first was the case with your truck. The addition of a free flowing exhaust freed the engine's ability to take in more air from the CAI already installed. As stated before, I believe that the Edge held your A/F ratio similar to stock, but I also believe that the tune did not provide a large enough increase in fuel for both the CAI and exhaust system you added, thus causing the lean issue.

Where I am not sure how O2 sensors play into the equation. I know that some vehicles (don't remember which ones right now) are very sensitive to changing them as well as changes in their placement. I don't know if this played any part in your situation or not, but I figured that I would toss that out there too.

Originally Posted by Longshot270

Take anything I say with a grain of salt because I'm no mechanic and certainly not an expert. I just type my best opinion and am willing to learn from the parts that are wrong. That is why these forums are so great. Technically I should be asking you for opinions, I'm one of the youngest members of this forum.

Longshot, don't be bringing age into the equation here. We each have one goal here, to exchange information and learn from the information someone else provides that we didn't already know. But since you brought it up...I'm only 27.


I've spent well over an hour typing this and I think I confused myself now, or maybe its just the fact that I have been up all night working and still have another 4+ hours to be up. If I missed anything, you have questions, or whatever, please let me know. I'm off to go play with some numbers to waste time. After I've slept, I'll try to post some interesting just for and giggles facts that I'm going to try to derive, now I've just got to find the excel files I have.

[Longshot270]

Good post Skip
But I want to add to a few of your points.

Originally Posted by Skip_1074

You never experienced a lean code with a CAI and the Edge because even though the Edge wasn't calibrated specifically for the CAI that you were using, it had altered your fuel trim already thus providing more fuel to the engine. That being the said, without actually knowing the strategies, or understanding them for that matter, that Edge uses (and many other factors such as tune used, octane used, CAI brand and tube diameter at MAF sensor in comparison to stock), I believe that your the Edge kept your A/F ratio with CAI somewhere around the what the stock programming had.

That is a good observation. One thing that is recommended for people with CAIs are the canned tow tunes. They are written with a richer A/F ratio and it helps counter act the lean effects.

But you also have to remember every truck runs a bit different so there is a bit of luck involved. He was lucky and no codes came up.

Originally Posted by Skip_1074

If you have a two hoses and pretend that the small one is stock and the larger is a CAI...lets say a 3" (7.07 square inch cross section) and 4" (12.57 square inch cross section)...and a sensor that is 1" by 1" (1 square inch) that extends into them. The sensor is designed to take a sample from 14.14% of the 3" hose and that is needed to provided accurate flow calculations, but when placed in the 4" hose, it only takes a sample from 7.95%. That means only 56.22% of the required sample is being provided for the calculations.

I bolded the part that I usually find important. Air is a fluid and fluid dynamics is a tricky subject. A more important comparison would be the velocity of a specific amount of air through different sized pipes. The engine is nothing more than an air pump so the air flow that is entering can be calculated mathematically. With the narrow pipe the sensor might read 65 grams/sec but with a larger pipe it might only read 55 grams/sec. That difference is what causes the lean condition because the truck fuels for 55 g/s instead of 65 g/s.

Here is where the O2 sensor comes in. Their purpose is to make sure the truck is running around stoic for emissions purposes. The O2 sensor will attempt to correct the issue but it does not have nearly as much influence when the MAF sensor is still operating within the predetermined parameters of "working sensor". When these two sensors do not agree enough you have rich and lean codes. But there are many other sensors that contribute to the codes.

Originally Posted by Skip_1074

Okay, on the the exhaust and addition to an Edge and CAI. "A chain is only as strong as it's weakest link." This works two ways on an engine:

1. You can only suck in as much air as the exhaust system can expel.
2. You can only expel as much air as the intake can suck in.

My understanding is the first was the case with your truck. The addition of a free flowing exhaust freed the engine's ability to take in more air from the CAI already installed. As stated before, I believe that the Edge held your A/F ratio similar to stock, but I also believe that the tune did not provide a large enough increase in fuel for both the CAI and exhaust system you added, thus causing the lean issue.

Where I am not sure how O2 sensors play into the equation. I know that some vehicles (don't remember which ones right now) are very sensitive to changing them as well as changes in their placement. I don't know if this played any part in your situation or not, but I figured that I would toss that out there too.

I can't say for sure but this echos the same effect as the CAI to the MAF sensor if you go to a larger pipe diameter with the same O2 sensors.

Originally Posted by Skip_1074

Longshot, don't be bringing age into the equation here. We each have one goal here, to exchange information and learn from the information someone else provides that we didn't already know. But since you brought it up...I'm only 27.

Only 27? You guys crack me up. Try being 19 a month ago, being 18 when I got promoted to a jr mod. You have to realize that, regardless of it being important or not, many people think age does make a difference. Doesn't help that I look 16 and have no official mechanical experience. My dad still refuses to let me work on my truck when I'm home. I was using the age as an example why the forums are good at building intelligent discussions because you can't assume somebody doesn't know what they are saying based on appearances, as I've encountered many times in face to face discussions.

Originally Posted by Skip_1074

I've spent well over an hour typing this and I think I confused myself now, or maybe its just the fact that I have been up all night working and still have another 4+ hours to be up. If I missed anything, you have questions, or whatever, please let me know. I'm off to go play with some numbers to waste time. After I've slept, I'll try to post some interesting just for and giggles facts that I'm going to try to derive, now I've just got to find the excel files I have.

Thats ok, I spend a few hours typing that long post too because I was watching a movie.
I usually go fishing to waste time...but whatever floats your boat.

[Jackpine]

Now that you youngun's have finished talking - and making VERY good points, in my opinion, I want to throw in this one last observation:

The MAF sensor is nothing more than a heated wire whose resistance changes as its temperature changes. As air flows over it, the wire is cooled and the voltage drop across it is modified. This voltage drop is what is interpreted by the PCM as a quantity of airflow - more air molecules hitting the wire, more cooling (which is what Longshot said in a different way). Notice if the area around the MAF sensor is increased, more air gets by without changing the number of molecules hitting the wire, and, the mixture is potentially leaner.

But, we have O2 sensors in the exhaust that report the result of that leaner mixture to the PCM and it tries to compensate by adding fuel. As long as the mixture is not TOO lean, it can do this and you don't get codes, but, you're now operating near one end of the design envelope (instead of near the center).

However, as Longshot also said (not bad for a "fish guy"), fluid flow is tricky stuff indeed. As flow velocity increases, static pressure decreases, so, the air becomes less dense. The effect of having a constricted intake snorkel forces the airflow velocity to increase to fill the cylinders at a reduced pressure! This is essentially the effect you get when driving at altitude. The MAF sensor "sees" all the flow though (as long as it fills the throat), so all is well. Opening the intake snorkel to 3" (an increase in diameter of 1" in my truck), changes the "choke point" cross sectional area from 3.142 sq inches to 7.069 sq inches! This doubling+ of the intake area greatly reduces the intake flow velocity and increases the density of the air charge - without "fooling" the MAF sensor since it still "sees" all the air flowing around it. (Effectively, we've suddenly taken the truck to below sea level atmosphere conditions and it can make more power.)

Anyway, this is how a 70-year old sees things.

- Jack

[ticopowell]

Haha well I am not the oldest or the youngest here(25), but I do think its great that we can all have fun joking about ourselves while learning stuff .
I just wanted to add a clarification to what I posted before, I am not interested in aftermarket MAF's, mine works fine and im never gonna have a monster machine that needs that much airflow. I was just pointing out that the diameter around the actual sensor stays the same on the CAI's that I have dealt with, therefor the fact that the rest of the pipes change wont have a huge effect on the reading.

also another thought... just because you arent getting a lean code doesnt mean that you arent running slightly lean... or the same with a rich code just my thoughts

[Longshot270]

Originally Posted by ticopowell

Haha well I am not the oldest or the youngest here(25), but I do think its great that we can all have fun joking about ourselves while learning stuff .
I just wanted to add a clarification to what I posted before, I am not interested in aftermarket MAF's, mine works fine and im never gonna have a monster machine that needs that much airflow. I was just pointing out that the diameter around the actual sensor stays the same on the CAI's that I have dealt with, therefor the fact that the rest of the pipes change wont have a huge effect on the reading.

Are you sure they weren't larger or a different shape around the sensor? If not then you aren't gaining anything running them besides the looks. You must consider your point of peak restriction as that will slow down air movement and change the absolute pressure from there to the cylinders.

[ticopowell]

It was the same diameter right next to the MAF, but it did remove other restrictions like in the fender, and it was a smoother path between the filter and the throttle body. Here is a good example of what I am saying about the CAI's I have dealt with. both were exactly this same idea.
the only think that I can think of that would affect airflow is that the air maybe be relatively faster or slower in that part of the tube versus what the stock tube would read. since this can affect that area without the MAF reading it (because like someone said the MAF covers only about 14% of the circle of air in question), that is why any adjustments would need to be made.

[Longshot270]

Originally Posted by ticopowell

It was the same diameter right next to the MAF, but it did remove other restrictions like in the fender, and it was a smoother path between the filter and the throttle body. Here is a good example of what I am saying about the CAI's I have dealt with. both were exactly this same idea.
the only think that I can think of that would affect airflow is that the air maybe be relatively faster or slower in that part of the tube versus what the stock tube would read. since this can affect that area without the MAF reading it (because like someone said the MAF covers only about 14% of the circle of air in question), that is why any adjustments would need to be made.

Well if the inside diameter of the housing is the exact same as the stock housing then you should be fine. The pipe after it doesn't matter and the open filter before it only affects performance through air temps. The issue is not that the MAF only covers 14% of the cross section, the issue is the air speed through the cross section. You are not measuring the actual mass of air, you are measuring a part of the cross section to determine the rate at which air enters. From there you can calculate the overall rate and then the mass of air passing through. You dont measure flow rates of a river by channelling it into a big cup. You find an area that has uniform flow, measure the rate there and the rate at which water is moving through the area. Increasing pipe diameter with the same air consumption rates causes the airspeed to lower and tell the computer to fuel less.

We are dealing with vacuum rather than pressure so the concepts are much simpler.

[Skip_1074]

Originally Posted by Longshot270

That is a good observation. One thing that is recommended for people with CAIs are the canned tow tunes. They are written with a richer A/F ratio and it helps counter act the lean effects.

I bolded the part that I usually find important. Air is a fluid and fluid dynamics is a tricky subject.

I usually go fishing to waste time...but whatever floats your boat.

When I read the OP, the combination of the Edge and CAI caught my eye while I was still on the first sentence, and I was actually surprised that nobody else mentioned it.

I understand fluid dynamics, but not to the point that I can confidently speak on it. You are definitely right about air being a fluid and it being tricky. I have searched a little today and I can't seem to find an article that I read on Banks Power, specifically addressing air being a fluid, but here a chunk borrowed from one of their articles:

Courtesy of BANKS POWER:

In the confines of a stock motorhome or truck, your gas or diesel engine’s inherent power is limited by factory restrictions in the intake and exhaust. With your engine starved for air, a tremendous amount of power traveling through the power-train is unnecessarily wasted before it gets to where it matters—your vehicle’s rear wheels. Airflow restrictions make poor engine efficiency, which soaks up fuel, runs a hot exhaust, compromises performance and shortens engine life.



How airflow restrictions waste power

* Intake restrictions cause engine to labor (“pumping losses”)
* Exhaust backpressure generates a tremendous engine heat-load
* Power is robbed from the crankshaft to expel exhaust
* Cooling fan runs often, wasting power and making the cab noisy
* Hot, overworked lubricants degrade faster and increase friction
* Gasoline-vehicle makers mask poor-airflow problems (eg. detonation) with overly-rich fuel
* Excess fuel is wasted, worsening mileage and emissions
* Inadequate airflow chokes engine’s potential

Think of an engine as an air pump that produces power. To run it, fuel is needed. In a typical stock vehicle, a gasoline engine produces only about 250 horsepower for every 1,000-horsepower’s worth of fuel put in. Diesel engines are more efficient—they put out about 320 horsepower for every 1000 in, only wasting 68%—still leaving lots of room for improvement!

Hampsterzone, you discussed backpressure in one of your earlier posts. As you notice, backpressure actually creates heat excess heat in the engine acting as a "parasitic loss" in power.

As for the time wasting that I did this morning, I was trying to do some calculations in regards to engine CFM airflow requirements in comparison to the ability of air systems to move them, but unfortunately I was unable to find the capability of the stock air system. But just for and , the max CFM flow of the 5.4L 3V engine at 5500 RPM is 628 based on the calculator that I have.

I would have gone fishing, except for a few things...its was only about 3:30am when I started the post, around 5:00am when I finished it and I'm pretty sure you can't get your line wet until first light. It was about 25 degrees outside and the closest place to go fishing is a GOOD hour plus away. The only reason that I was still up was my daughter had late start at school and I had to take her so my wife could go to work.

This discussion has been great and I only hope that we can keep the information flowing. If I find the article of air as fluid, I will definitely pass it on.

[Longshot270]

Originally Posted by Skip_1074

When I read the OP, the combination of the Edge and CAI caught my eye while I was still on the first sentence, and I was actually surprised that nobody else mentioned it.

I understand fluid dynamics, but not to the point that I can confidently speak on it. You are definitely right about air being a fluid and it being tricky. I have searched a little today and I can't seem to find an article that I read on Banks Power, specifically addressing air being a fluid, but here a chunk borrowed from one of their articles:



Hampsterzone, you discussed backpressure in one of your earlier posts. As you notice, backpressure actually creates heat excess heat in the engine acting as a "parasitic loss" in power.

As for the time wasting that I did this morning, I was trying to do some calculations in regards to engine CFM airflow requirements in comparison to the ability of air systems to move them, but unfortunately I was unable to find the capability of the stock air system. But just for and , the max CFM flow of the 5.4L 3V engine at 5500 RPM is 628 based on the calculator that I have.

I would have gone fishing, except for a few things...its was only about 3:30am when I started the post, around 5:00am when I finished it and I'm pretty sure you can't get your line wet until first light. It was about 25 degrees outside and the closest place to go fishing is a GOOD hour plus away. The only reason that I was still up was my daughter had late start at school and I had to take her so my wife could go to work.

This discussion has been great and I only hope that we can keep the information flowing. If I find the article of air as fluid, I will definitely pass it on.

In scientific terms, a gas IS a fluid just as a liquid IS a fluid. The confustions arise when things are translated to common speak because words are not the same.

If your wanting flow bench results, we have some in an ancient article...
http://forum.gopowerhungry.com/2004-...t-results.html

At the current state of technology, our engines are pathetic on mechanical efficiency.

Back pressure also reduces engine efficiency because not all of the exhaust gasses are expelled. For gasses, pressure is equivalent to mass. Here we work backwards. Instead of trying to increase pressure at the cylinder, here we are trying to reduce it. If there is pressure out side of the cylinder then more of the molecules that make up the exhaust gas will stay in the cylinder. Things also start getting real tricky because the exhaust gasses start acting a little different because now we are pushing them with pressure rather than pulling them. You encounter simple logic problems such as exhaust pipe diameters and configurations that reduce performance rather than increase it, along with true impact of obstructions and such. If you go on the larger forums you can see people (like me haha) get chewed on for running baffled mufflers like the flowmasters. The baffles present an obstruction and logically would stop or hinder the flow to cause a decrease in exhaust flow, increase heat, etc. All of that sounds true and to an extent is true, I did see a loss in performance because I tested it at a local drag strip. I lost .07 seconds on a quarter mile run. Exhaust requires more advanced understanding of fluids under pressure because it is very easy to overeastimate and undereastimate the effects of a modification without having a solid understanding of the numbers that cause it. I try to not discuss anything unless I'm able to test it because without facts everything is a WAS guess, epecially for this.

[88Racing]

To put it simply a cai alters the original path of air in which the MAF was calibrated for......
Also
Larger diameters of tubing cause the air intake to move slower across the MAF at a set rpm thus less fuel is delivered bring in a lean condition.....