The CAI arguement explained... - Subaru WRX Forum
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post #1 of 60 Old 07-07-2004, 03:16 PM Thread Starter
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The CAI arguement explained...

Okay. The subject of a cold air intake on a WRX is a very hotly debated topic as of recent. I feel it's time I explained to you what the REAL problem is. A cold air intake is not bad. Cold air is always better than hot air. Even on a WRX.

Having said that, however, I must explain why everyone (including myself) advises against them for the WRX:

The DESIGN of the cold air intakes is the problem. If you look at the cold air intake, the filter is located inside the fender. For the filter to connect to the inlet of the turbo, the air has to travel through a pipe running through the inner fender and then to the turbo inlet hose. The problem is the way the pipe has to curve just after coming out of the fender to meet up with the stock turbo inlet hose. It makes a rather severe turn, then goes past the MAF sensor, then makes another sever turn. The turn right before the MAF sensor is the problem. It makes the air flow past the MAF sensor at a different angle then the MAF is used to seeing. That is what causes the lean conditions.

http://www.cosmo-graphics.com/temp/CAI.jpg

That is also why short rams don't have that problem.

http://www.cosmo-graphics.com/temp/short_ram.jpg
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post #2 of 60 Old 07-07-2004, 04:12 PM
 
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Sticky and FAQ section
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post #3 of 60 Old 07-07-2004, 07:20 PM
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hehe it will last a few weeks then they will ask again =P... also, I will be testing the a new CAI (can't say which) on a stock wrx this weekend (installed for a client) which is said to have correct MAF readings by over bending the first corner (almost 140 degrees) I guess the O2 and MAF readings will tell if there is a change; if its good I'll post the brand later.

-kobi
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post #4 of 60 Old 08-10-2004, 01:19 AM
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Quote:
Originally Posted by IBAUCLAPla
Sticky and FAQ section
Not sure if it's cool to post on here. Not really sure if this means I'm supposed to go to another section or what? Kind of a noob hehe. But here goes my 2 cents anyway.

The reason I don't recommend cold air intakes for turbocharged applications is this. The main reason for a "cold air" intake is to get lower temperature air from outside of the hot engine compartment. This is fine if the air is going straight into the intake manifold. But for a turbo application, this air goes into the compressor inlet. With the compressor spinning at super high RPMs it gets very hot as does the air. So whether it came from outside of the engine compartment or not won't make a huge difference here. Thus, God gave man the intercooler The second intension of the cold air intake, or any intake for that matter, is to ram as much air as possible into the intake manifold, or in our case, supply the most air to the compressor. So I think the key in our situation is which intake will give you the most airflow. As far as this causing a lean condition, I'm not too sure about this. I'm sure the guys more savy with engine management could tune that out pretty easily.

Well, let me know what you guys are thinking. I'm still learning so please tell me if I'm wrong.

Joel
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post #5 of 60 Old 08-10-2004, 02:00 AM
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ok kids, took my CAI out of mothballs and put it back on. 2 days later, pow a CEL p0171 system lean bank 1. took off the pipe that goes into the fender, clamped the filter to the pipe inside the engine bay (with the bend before the meter), cleared the code and drove the car. 4 drive cycles later, pow the same code! took off the shortened CAI pipe, cut the bend off before the MAF sensor, reclamped the filter and drove it again. been 4 days, no cel, no wierd off-idle problems, no very high EGT's, everything is ok so far! although I butchered up an expensive CAI, I wanted to see if the bend in the pipe really was the problem. so far it was...will keep everyone posted if I get a CEL.

[I]"Winners never quit, quitters never win, those that never win or quit are idiots."[/I]
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post #6 of 60 Old 08-10-2004, 08:37 AM
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what is mentioned above is what is generally refered to as MAF turbulence....


the EVO i have been tuning on has had the same issue with the K&N on it, we added a shroud around it, and solved the AF ratio jumping around...



of course, alot of the ebay intakes have different size piping, and since the WRX uses a drop-in MAF, there is more air flowing in the car than it is calibrated for, causing the lean condition.

class dismissed.
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post #7 of 60 Old 08-10-2004, 11:17 PM
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another day, no CEL

[I]"Winners never quit, quitters never win, those that never win or quit are idiots."[/I]
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post #8 of 60 Old 09-12-2004, 07:52 PM
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Alright, I understand the idea of the car running lean because of the velocity of the air making the bend going into the maf from the cold air section, but I honestly can't remember from installing my short ram if the sensors in the MAF go right down the middle, or if they're at the bottom side of the sensor, or where. My thought is this...I have the cold air portion for my Perrin intake, but it's just not installed. What if, when installing the maf section in the pipe, you rotate the actual maf, so that the velocity around that corner remains the sees a different amount of air depending on which way you rotate? I know with mustang guys, they call this their "dark horse" mod, the rotate the maf to lean out or richen the a/f mixture. I will have to check this tomorrow while at work and let ya'll know. Anyone else have this thought? With that hard intake pipe guys it'd take modification to the mpipe, Perrin guys just rotate and re-clamp.

-Curt
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post #9 of 60 Old 09-13-2004, 07:16 PM
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Not trying to say you guy's are wrong or right but I have the Injen CAI with my computer tuned (Ecutek) which Speed sport tecnik (Norwalk CT.) recremended and I have no problems. The CEL was on pryer to tunning but that came on when I did the down pipe.
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post #10 of 60 Old 09-14-2004, 10:22 PM
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that is because you have tuned for it.....
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post #11 of 60 Old 09-15-2004, 01:09 AM
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still no CEL, had a wideband on the car last weekend, everything is running perfect. I firmly believe the bend in the pipe was the only issue my little experiment uncovered.

[I]"Winners never quit, quitters never win, those that never win or quit are idiots."[/I]
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post #12 of 60 Old 11-02-2004, 11:07 PM
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I have the same code p0171 but i am running the stock intake with no silencer. could that be causing the code?? I just thought it was my downpipe causing the cel.
i know there is also alot of argument about the silencer being good or bad but if you think that is the problem i will put it back on.
Thanks for your time
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post #13 of 60 Old 11-03-2004, 12:33 PM
 
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I highly doubt that is your problem.
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post #14 of 60 Old 01-04-2005, 04:26 AM
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i had a cai and today i just sawed off the corner at the end of the short ram version of it and its running so much better. and no code yet
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post #15 of 60 Old 01-06-2005, 06:28 AM
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Air filter box sensor...

Hi! There is a sensor in the stock air filter box. When installing a cold air intake, is it imperative to keep using this sensor? Can we simply unplug it?
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