[Former_Boosted_IS]

The question is...??? Does a Cold Air Intake (CAI) actually reduce Air Inlet Temperatures (AITs) over a Dual Cone Intake (DCI)? Or are intakes simply for getting adequate air flow? This is the question that has been thrown around on the forums a lot and I personally have participated in many of these discussions. The conversations go back and forth with theoretical arguments and no hard facts. What we do know is colder air in the engine equals more oxygen in the combustion process and more power if everything flows the same. Honestly, I wasn't sure I wanted to put in all the hours of work to answer this question. Well, needless to say I decided that I wanted to know the answer, so here we are.

Products Tested

This test was an AIT analysis between the BMS DCI and STETT Performance Cold Air Intake. I want to start by saying both companies have been very, very easy to work with and knowingly participated in the testing. We as a community owe Terry at BMS and Chad at STETT Performance a huge thank you for helping me to make this independent testing happen.

Testing Procedure

Tests were conducted to determine how the STETT Performance CAI and the BMS DCI would perform in multiple situations. I collected nearly 70,000 data points over the last 3 days in a specific testing procedure. Each test was conducted in the following way:

1) JB3 8D4 Rev.4 on map 7 (same as map 6 on 1.2).
2) This is critically important to note... the car has an Active Autowerke Intercooler.
3) Car was warmed up for 18 minutes in identical driving routes, rpms, and speed.
4) Data was logged using Bavarian Technic software and BMS Tuning Tool.
5) Ambients were logged in an attempt to replicate similar conditions.

Four tests were done on each intake using an identical car setup. The tests are:

1) Approximately 10 minute highway runs at 70 mph
2) Approximately 10 minute standing idle
3) Approximately 10 minutes of stop and go driving
4) 3 back to back wide open throttle (WOT) full gear pulls

Ambient Conditions

The BMS DCI was logged under the following conditions:

Temperature of 67 degrees F
Relative Humidity of 54%
Pressure of 30.15" / 1020 mb

The STETT Performance CAI was logged under the following conditions:

Temperature of 70 degrees F
Relative Humidity of 84%
Pressure of 30.09" / 1018 mb

Note the BMS DCI was tested at 3 degrees F colder temperatures and 30% lower relative humidities.

Results

Highway Runs

I am going to start with the highway runs because these we would expect to be identical. These tests were done at 70 mph with about a 2 minute turn around in the middle of the runs. You can see where the AITs rise slightly while waiting at the stop light.

Here is the AIT graph of the BMS DCI



Here is the AIT graph of the STETT Performance CAI



Both showed very consistent results. Around 82 degrees F through the entire highway runs. No difference at all between the BMS DCI and the STETT Performance CAI.

Idle for 10 minutes

This was a simple test. Let the car sit after the highway run for 10 minutes.

Here is the BMS DCI AIT graph:



Here is the STETT Performance CAI AIT graph:



The BMS DCI graph shows the AITs warm up faster in the first 5 minutes or so, then they become very close by the end of the ten minutes. The BMS DCI was at 112 degrees F after 5 minutes while the STETT Performance CAI was at 106 degrees F. The BMS DCI was at 121 degrees F after 10 minutes while the STETT Performance CAI was 119 degrees F after 10 minutes. The STETT Performance CAI definitely performed slightly better here with colder AITs.

Stop and go driving

It is important to note here, there were a few more stops in the testing with the BMS DCI only because I got stuck at more lights.

BMS DCI AIT graph versus RPM:



BMS DCI AIT graph versus speed:



STETT Performance CAI AIT graph versus RPM:



STETT Performance CAI AIT graph versus speed:



I have to say both performed nearly identical to one another. Both hovered from 85 degrees F to 95 degrees F during the entire runs. The single most noticeable thing was that during hard acceleration the STETT Performance did seem to drop AITs faster, but I would not give an advantage to either.

3 wide open throttle long gear pulls

Ok, this is the big daddy and the single most important test I did. There is one piece of bad news. I accidentally cleared the first run off one of my data logs from the Bavarian Technic software, but did log the run using the BMS Tuning tool. The bottom line is the graphs will show run 2 and run 3.

From the BMS Tuning Tool Run 1 on the BMS DCI produced a peak of 109 degrees F and the STETT Performance CAI produced an AIT of 101 degrees F. I apologize for no graphs, but the next two graphs show more than enough.

AIT graph of run 2 and 3 on the BMS DCI:



AIT graph of run 2 and 3 on the STETT Performance CAI:



AIT graph of run 2/3 of the BMS DCI versus the STETT Performance CAI:



The data is very clear here. The BMS DCI had a peak AIT that was 8 degrees hotter on run 1, 10 degrees hotter on run 2, and 8 degrees hotter on run three. This is an average of 8.7 degrees hotter for the BMS DCI over the STETT Performance CAI over the three runs.

The analysis of the graphs clearly shows the entire temperature climb is shifted down by the STETT Performance CAI. There is no exponential difference, but a step difference between the two. You can also see the difference is held through the 1 minute or so it took me to turn around for another run. The data is pretty definitive.

Conclusion

It must be noted that this testing was done with an Active Autowerke Intercooler that has an efficiency of 80%-90% versus the stock intercooler with an efficiency near 50%. The difference in AITs will be magnified if you have a stock intercooler.

Second, the JB3 would lower boost on the high end if the engine was not getting enough flow from the intakes. The boost was logged and identical between the WOT runs.

Despite the STETT Performance CAI being tested in 3 degree warmer weather and 30% higher relative humidity it still out performed the BMS DCI in the WOT long gear runs. Without a doubt, the data proves that a CAI does cool AITs in WOT runs and while idling under 5 minutes. The difference in AIT numbers was nearly 9 degrees F between in the WOT long gear runs.

The question was:
Does a CAI produce colder AITs or is cooling AITs the job of the intercooler?

The answer is:

Yes. The STETT Performance CAI does produce colder AITs then a DCI intake.

EDIT EDIT EDIT

Added FATS Style Testing Section

Ok, I have done FATs style testing on the 2nd run in the data log (first on the charts). This is for 2nd through 3rd gear because I could verify 100% throttle on both runs in this section.

DCI FATs style time = 7.69 seconds
STETT CAI FATs style time = 7.47 seconds

That makes the STETT CAI 0.22 seconds faster through the 2nd to 3rd gear pull.

This then means the STETT CAI produced 8 degrees colder AITs in that run and the car was 0.22 seconds faster from 2nd through 3rd gear.

[Former_Boosted_IS]

One other thing, to say that the Bavarian Technic software is incredible is an understatement! If you own a BMW you simply must own this software!

[goowatchi]

Wow, much kudos for your time/effort in testing the performance of these two intakes! It would be interesting to have a control so we can see how well the stock intake fared with similar conditions.

[FotiosF90M5]

great analysis and thanks for taking the time and doing such a good job with the testing. big thumbs up!!

[danniexi]

Now what I want to know is whether the stock intake produces colder AITs then the DCI.

Great review! Thanks for taking the time and collecting all of this data. I think what's most important is that we all need an aftermarket intercooler over stock. Despite the differences between DCI and the CAI, I think you made a very good point in saying that "the difference in AITs will be magnified if you have a stock intercooler."

[canrhea]

nice work.. Im not too surprise at the results either but you shuold also do a stock air box test just to make results even more solid

[cn555ic]

Thanks for the testing, I am glad I went with a CAI based on your testing and data! ALthough the temp difference was only 3 degrees, the humidity was much more significant when tested with the CAI, making conditions worse for the CAI and it still came out ahead from your tests!

[ragingclue]

Originally Posted by canrhea

nice work.. Im not too surprise at the results either but you shuold also do a stock air box test just to make results even more solid

+1 and drop-in

[cincy335i]

Thanks for this test and the great write up!

Cheers to you!

[Zeph]

Nice job! I did notice though that your idling results you got mixed up. The graphs show the DCI to actually be slightly cooler but your typed results underneath show the STETT to be slightly cooler (so basically about even considering the air outside). You were right about the DCI going up "faster" in the 1st 5 minutes, although very slightly.

So basically the STETT CAI might be slightly better with back to back WOT's like a serious track event of non-stop drag racing. Not sure if you can actually make much out of an 8 degree difference when up in the 115 degree range for hp/tq but it is interesting somewhat to know.

I agree, point here is clear... stock FMIC has to go regardless of what you do with any other mods

[sflgator]

First, let me just say THANK YOU, Former_Boosted_IS for all the time you spent on this testing and all your efforts in getting this unbiased data to all of us!!!

Secondly, although there was a 9 degree drop in AIT with the Stett CAI, I still wonder if this temp drop is enough to make a real difference in power. I understand that temps too hot will make a piggyback pull back a bit, but I thought this CAI was supposed to be pulling in more ambient air from the outside (especially while driving fast like on the hwy and/or at WOT). It just seems like we should have seen more like a 15+ degree drop in AIT, especially since the outside temps during your testing were relatively cool (in the upper 60's - low 70's F). What would happen if these tests were done in a more tropical climate where the weather is typically in the 80's with high humidity?

Lastly, we've got to wonder now how the oem stock intake (with or without air scoops) perform in regards to AIT in comparison to the BMS DCI and Stett CAI?

Maybe I'm just playing devil's advocate here, but I think these questions still remain unanswered. Hey, if this Stett CAI (and I assume others companies would follow with more true CAI's for the N54 engine) really does make a significant improvement to the N54 engine, then I would absolutely consider this CAI for my 2010 335i Coupe I have on "pre-order." . Thanks again for ALL your efforts and sharing all this info with us!!!

[cn555ic]

Well there was always two companies that had TRUE CAI in the market....STETT and UR

[Zeph]

Any difference in dyno or 1/4 mile trap speed between these 2 intakes? I think you just saved me a few hundred dollars realizing I don't need to waste money on a CAI or Injen, etc... BMS @ $99 is winning IMO

[Septro]

Do you have Scoops installed? I'm curious if that makes a bigger difference for the highway and WOT runs if you are forcing air over the DCI cones with the scoops and snorkel as compared to the CAI.

[flukey]

what a post. thanks for the effort man!

im glad i picked up that ur cai....

[ThorsHammer]

So then the next questions are: Does a DCI provide more volume than a single CAI? Further, does the volume of air provided make a difference, respective AND irrespective of AIT? And finally, does filter location for a DCI make a difference in AIT? For instance, Injen vs. BMS?

[ragingclue]

Originally Posted by ThorsHammer

So then the next questions are: Does a DCI provide more volume than a single CAI? Further, does the volume of air provided make a difference, respective AND irrespective of AIT? And finally, does filter location for a DCI make a difference in AIT? For instance, Injen vs. BMS?

You know, I'd be satisfied with true CAI vs Drop-in vs DCI

You can't test everything from every angle with every possible mod. But it would be nice to have a base understanding of what each of these concepts does for whom. And a DCI at $99 vs a CAI at $400 or free with a $910 IC, there are some variables thrown in... But those variables are afterthoughts. We just want straight up number comparos for each concept; doesn't matter which company is the guinea pig to me...

[Sniz]

excellent post. well done.

me and O-cha were the 1st 2 to have the CAI installed on our cars way back when...it was the UR intake. I liked it, think he did too.

I never had plans on replacing it with an open element setup (dual cone, etc.)......this confirms what I thought.

[ThorsHammer]

Originally Posted by ragingclue

You know, I'd be satisfied with true CAI vs Drop-in vs DCI

You can't test everything from every angle with every possible mod. But it would be nice to have a base understanding of what each of these concepts does for whom. And a DCI at $99 vs a CAI at $400 or free with a $910 IC, there are some variables thrown in... But those variables are afterthoughts. We just want straight up number comparos for each concept; doesn't matter which company is the guinea pig to me...

I think there are just too many variables to be honest.

It really comes down to how many molecules of oxygen are present with each combustion. We know from chemistry that the colder the air, the more densely populated the molecules are per relative volume.

So my point is, which provides more volume/quantity of O2 molecules? On one hand, the air is colder (CAI). On the other, there is more air present (DCI).

Maybe...just maybe...they balance each other and that's why it's so hard to prove/disprove that one is better than the other?

[ragingclue]

Originally Posted by ThorsHammer

I think there are just too many variables to be honest.

It really comes down to how many molecules of oxygen are present with each combustion. We know from chemistry that the colder the air, the more densely populated the molecules are per relative volume.

So my point is, which provides more volume/quantity of O2 molecules? On one hand, the air is colder (CAI). On the other, there is more air present (DCI).

Maybe...just maybe...they balance each other and that's why it's so hard to prove/disprove that one is better than the other?

True.

But a side-by-sided-by-side of a DCI, CAI, and drop-in in all conditions (track, drag, city, etc...) would pretty much give us a good idea if there was a general sway in any direction worth noting. I'm not looking for specifics. Just general data. Or rather specific data that will support a general conclusion, but I know that's pretty much out the window.

[krapnoj]

Great post and work!

Feeling good about my Stett CAI!

[addicted2drums]

nice review.