CAI indepth.....

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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.