DIY CAI stock intake mod

I looked for any DIY threads similar to what I did and could not find any.

Since I decided to tune my Denali going with EFI from MJ Engineering which I ordered yesterday.
I did my DIY intake mod which really woke up my engine.
Using K&N drop-in airfilter which I have had in since 2008.
I can only imagine how well it will run once I get the EFI AutoCal tuning.

I did this mod to my Dmax in 2008, it worked very good and the gains was similar to others that had Banks RamAir and S&B CAI intakes.
The Intake Ambient Temps dropped 20-25 degrees and the MAF g/s @ idle went from 26-28 to 40-42, using aFe ProGuard 7 drop-in airfilter.
Monitoring PID's using the Edge Insight on my Dmax.

The nice thing about doing this compared to buying a CAI you don't have to worry about MAF location issues.
Cost about $45-$50 for the K&N and about 2 hours labor.

Thanks for the write up, I'll have to give this a try.

Helidriver said:

Thanks for the write up, I'll have to give this a try.

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As far as seat of the pants testing this was more noticeable on my Yukon Denali than it was on my Dmax.
I used a combination of these tools depending on what was the easiest to use.
Remove the filter from the box when cutting and be careful when cutting around the foam seal.

looks similar to what i did! looks stock and its stealth! makes it possible to use the stock intake with my magnacharger and put my banks power intake in the bench :0

I was looking at my dmax and its open like that but on our denali its got a different edge that runs on fender with two opens that line up with two slots on the fender. Is the 03 denali a different box. Or did you just cut yours before pic and cut fender as well not scared to do either just wondering if mines different for any specific reason


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These are before and after on my 07.5 Dmax I also cut out the intake to match, the same as I did on my Denali.
As far as the 03 I don't know

One can't compare a Duramax to a gas engine, two different animals. Some could consider doing that on a light colored vehicle, but we see higher air temps with dark colored vehicles due to the fender being hotter.

JennaBear said:

One can't compare a Duramax to a gas engine, two different animals. Some could consider doing that on a light colored vehicle, but we see higher air temps with dark colored vehicles due to the fender being hotter.

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Considering the Denali and Dmax's air boxs are in the same location pulling from the inside passenger fender and both of my vehicles are BLACK.
So that theory does not play a part in this MOD, only the comfort inside the vehicle is affected.

Both of my vehicles IAT's are the with-in 2 degrees of the outside temps, with Phoenix Az hitting 115-122 in the summers and I'm getting these lower #'s then the color of the vehicle does NOT play a roll.
Besides the MAF g/s at idle was doubled on the Denali along with the IAT's and outside temps with-in 2 degrees.
If the vehicles color played a part in this then the IAT would be much higher than outside temps. They are not.
Plus there was a very noticeable gain in performance with this MOD over just having a K&N or even having a AirRaid Jr kit.
Without this MOD the IAT's was about 20 degrees hotter and the MAF g/s was 1/2 of what I have now.
And that was with only having a K&N OEM drop in which has been in for almost 6 years, cleaning every year.

My Denali MAF g/s at idle in park now is 8-9, my Dmax went from 26-28 to 40-42at idle in park the reason its higher is because its turbo powered.
If anyone thinks that more cooler airflow would not/will not help then I would have to question their knowledge on vehicles.
More air flow now you can add a little more fuel which equals more power.

Even my EFI tuner noticed a large increase in airflow, more than what he has seen and had to adjust for that in the tuning.
So I will have to dis-agree.
Beside I do know they are two different animals if anyone thought different they are fools.

Idle airflow is fixed on a gas engine. If you increased to 8-9g/sec, then your idle rpm had to increase. Diesel engines operate at wide open throttle, varying fuel for power creation. Gas engine utilize a very specific fuel flow for a given airflow. More air= more fuel= higher rpm.

Justin having tuned thousands of trucks of all colors in all environments in person and on dynos(including Phoenix last week) we can empirically state with complete confidence that, no intake will operate that close to ambient.

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---------- Post added at 11:41 AM ---------- Previous post was at 11:40 AM ----------

If you are seeing higher g/s then your throttle is open more.

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Well maybe you have not run into this yet, I have.
95 degrees outside temps, IAT 97 degrees.
Idle is the same, MAF g/s @ idle increased from 3-4 to 8-9.
Now I'm certainly not going to change anything, the Denali runs absolutely much better than it did before I did this mod even before I went EFI.
Besides this is not my first rodeo dealing with tuning, 35 years the real old school tuning days modifing the intakes and re-jetting the carburetor.
And now 10 years with this computer stuff.
The color of the vehicle has absolutely NO bearing on the intake temps, considering the air flow comes thru the fender under the vehicle.
If people want to listen to you, then it's there loss and they are missing a inexpensive way to have more power.
The next time your coming to Phoenix contact me I'll meet you anywhere and I'll prove you'all, that your very wrong.
How about we meet at CHUCKS SPEED & RV in Phx and we'll put my Denali on the Dyno so you can see for yourself.

FYI, any engine old school or computer if you can make more air flow available and give it a little more fuel it WILL run better and have more power.
If you contradict this then people should be real concerned, I've already got my EFI tuners,

Justin was just in Phoenix last weekend and can likely pull up a few logs from different times of the day (with similar air temperatures). He also teaches the EFILive classes and has countless hours across the nation with vehicles on dynos, so I think the data we have is pretty darn accurate. But that is neither here nor there. The dyno numbers will always be different than that of a vehicle that is sitting in the baking sun; two different scenarios.

In terms of idle airflow, in a gas engine, you are not understanding what I was saying, nor how the engine works. Your engine's idle airflow is a function of the throttle blade. Period. More airflow at idle is due to the throttle being open more, less is due to less (or a vacuum leak). Within your ECM, there is a table that explicitly defines the idle airflow needed to maintain a specific RPM. Too low of airflow and the ECM will open the blade more to compensate, too much and it will close the blade. For you to see a change in airflow shows that you either had a vacuum leak that was allowing 3-4g/sec of unmetered air into the engine or something else has changed (like, a higher idle RPM or significantly reduced ignition timing). Further to that point, your engine cannot idle at the OEM 525rpm on 3-4g/sec of actual airflow. More is needed, hence the 6g/sec defined in the minimum idle airflow table.

These new fangled engines are quite a bit different from 30 years ago, and you are right, computers have come a long way. I am not saying it is not worthwhile to do, just saying your numbers seem to be off. To say that color will not be a factor in such an extremely hot climate such as Phoenix where air is drawn in against an outside metal component runs contrary to physics and heat transfer. If color made no difference, you'd find more houses painted a dark color, dark-painted aircraft (try and find a Cessna whose wings aren't white), etc. For actual data, a 2 second google search proves the point, empirically: http://www.tom-morrow-land.com/tests/cartemp/

I will also note that the box is not the restriction on these intakes, it is the tube. Were the box a restriction, the Airaid tube with the OEM box would have underperformed on our dyno testing. But I digress...

Personally, my time and money is better spent on an off the shelf intake tube, but to each their own. I am merely pointing out other factors to consider, as this a forum to supply information on.

2 hours labor plus $40-$50 for a K&N for something that works very good VS what ever a intake tube cost. If $$$ is tight for a person that would be up to them.
Even if I went with a tube I would still suggest doing the DIY Mod.
Yes the air box is in the hot engine compartment but the air flow is not being pulled thru the hot engine compartment.
I've done intakes in the past and I've never been impressed, nothing beats opening up the fender and air box for more air flow on the stock intakes.
Some have drilled holes in the air box (bad idea) or buy a aftermarket intake with the air filter open to the hot hood. Your letting in all that hot engine compartment air in and the IAT's will be high.
Having cooler air flow the engine will run much better even on a gasser.
I even wrapped my complete air box and tube with insulation on my Dmax, the only gains was when idling for long periods the IAT would rise pretty high 165 with the insulation max IAT on long idling is 145.
This is when it's 115-120 outside even in the shade idling.
As soon as I start driving within 1/4 mile the IAT is within 2 degrees of the outside temps.

D_R_C said:

I've done intakes in the past and I've never been impressed, nothing beats opening up the fender and air box for more air flow on the stock intakes...

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Actually, replacing the intake tube beats opening up the fender/airbox. As a point of reference, you should read the dyno comparison in the Black Bear Performance forum. The tube has been identified as the single biggest restriction in the intake path; replacing just the tube with the Airaid Jr tube yielded some impressive results. If the airbox were a big point of restriction, then the results of the Volant kit would have been much more impressive.

What you've done here, essentially, is port matched the airbox to the fender. I will likely do some variation of the same thing on my Tahoe - but not as a standalone mod. I'll be replacing my intake tube as well with one of the Airaid kits. More air is a good thing, and I think that both mods would compliment each other pretty well.

Good free mod though, it surely can't hurt anything. Thanks for the write up.

Thanks,
The performance tests did not include a mod like this, I could not find it.
I agree the intakes help but this will help even more. As far as this being a standalone mod, for me I'm very happy with this alone.
Considering the low cost, about 2 hrs labor and the cost for a aftermarket air filter or you could still use the stock filter.
For someone on a tight budget for instant power you can't beat it. IMO.

These stock intake mods are not new to the world, do a internet search on the subject.

Type in the search "DIY CAI STOCK AIRBOX MOD" mine is in there along with several others.
You can also try "DIY STOCK INTAK MOD" ETC,ETC you will find many links on this subject and your will have several hours of reading with positive results.

"ALOHA"

I understand the concern of the air being hotter behind the fender, but since that is where the stock box draws air from I can't see how opening that up would change the air temp any.
I also have seen an air raid MXP box that has a tube that goes down and pulls air from just behind the bumper. Would this air be any cooler? If so, that might be an easy DIY mod also.

JeRM number 9 said:

I understand the concern of the air being hotter behind the fender, but since that is where the stock box draws air from I can't see how opening that up would change the air temp any.
I also have seen an air raid MXP box that has a tube that goes down and pulls air from just behind the bumper. Would this air be any cooler? If so, that might be an easy DIY mod also.

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Its not changing the air temp to be cooler it's allowing more airflow thru the opening which will help reduce the IAT and raise the MAF g/s.
Doing the Airaid MXP box with tube/scoop would result in pretty close to the same results, it just costs more.
No matter what you buy or do the IAT's will never be cooler than the outside temperature.

The IAT's on my Denali is with-in 2 degrees of the outside temperature, if the air was hotter behind the fender I would NOT have these results.
Example 95 degrees outside temp, IAT 97 degrees, the MAF g/s stock at factory idle is 3-4 with this mod factory idle 8-9.
You will not see these positive gains unless you do something similar like the Airaid MXP box with scoop or some type of airbox mod to open up the area for the air being pulled thru the filter.

If you look at the pictures on my first post the factory fender and airbox openings are smaller than the airfilter surface, this is restriction.
By opening it up like I show, you will have more airflow available with no restrictions.

The color of the vehicle plays NO part in this mod at all, like you said this is where the factory openings are, its just bigger now.
This is just a cost savings DIY CAI that works pretty good compared to buying a CAI.

If a person has the $$$ to shell out then by all means go out and buy a CAI.
If your strapped for cash but still want to do something then consider doing a DIY, any DIY.
I am not strapped for cash, but I do know my results are just as good/equal compared to any other aftermarket CAI.

Beside a person would never know unless you told them or they pulled the airbox.
You just don't want to open up the airbox inside the engine compartment letting the hot engine compartment air in, this is not a positive gain.

This is why I suggest doing a internet search on this subject and you will find 100's of links with people doing similar mods. Most said they are all happy they did a DIY saving $100's of dollars.
I have NOT read anywhere anyone stating they wish they never did a DIY intake mod.
I don't know of anyone that has to get the approval from anybody to do a DIY mod.

This is not completely my mod, what the original person did was just the airbox, I implemented the opening up the fender to match the airbox which lowered the IAT another 10 degrees to where it's with-in 2 degrees of the outside temps.
This really helps when towing keeping the temps lower.

I did the airbox mod and threw in a K&N 2 days ago and the butt dyno liked it. I didnt open up the fender but I am considering it. In my opinion the intakes out there are WAY OVERPRICED!

This is on my list of things to do tomorrow. Along with plugs, wires, catch can install and an oil change.

When I first did this DIY on a vehicle I was a little chicken, I was hesitant but I did it anyway.
The first thing I did was just open up the the airbox and drove it for a few days, and did some monitoring, it was a positive improvement.
After noticing how small the opening was in the fender, I then pulled the airbox and opened up the fender, even a better improvement.
I've always monitored with gauges, what I've done.

I agree aftermarket intakes are a little pricey, but if something like this works pretty good, and IMO it does.
Why spend the $$$, especially when some intakes relocate the maf sensor, which could cause issues, it has for me in the past.
Plus it still looks stock, I'm all for it, no one knows except whoever you tell.