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Discussion Starter · #1 · (Edited)
Friday night I installed the Cobb intake. I've been running a closed end K&N filter since I got the car. Cylinder corrections were always between -1 and +4. For poops and giggles I decided to put the open end supplied filter in when I installed the tube. It seemed to increase the range of cylinder corrections. Around 60 miles over two different drives I saw negative corrections of -1.72 and positives of +4.28 without doing any actual pulls. Interesting. So I put the K&N back in yesterday. So far my worst negative correction was -.29 on one cylinder on a full 3rd gear pull. Can anybody make sense of this? I'm thinking possible false knock from from the sound of the open end filter.

Edit: Should be CYLINDER corrections. My bad. Can a mod change the thread title please?
 

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Friday night I installed the Cobb intake. I've been running a closed end K&N filter since I got the car. Cylinder corrections were always between -1 and +4. For poops and giggles I decided to put the open end supplied filter in when I installed the tube. It seemed to increase the range of cylinder corrections. Around 60 miles over two different drives I saw negative corrections of -1.72 and positives of +4.28 without doing any actual pulls. Interesting. So I put the K&N back in yesterday. So far my worst negative correction was -.29 on one cylinder on a full 3rd gear pull. Can anybody make sense of this? I'm thinking possible false knock from from the sound of the open end filter.

Edit: Should be CYLINDER corrections. My bad. Can a mod change the thread title please?
Just to remain consistent, same fuel was used? Relatively same conditions during testing?

Those corrections are very similar so pretty small differences could have caused the corrections to vary, however I'm all ears for any other input from someone. I've never had issues with my open ended filter, but also see regular -1.72ish corrections with current setup and fuel.
 

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Discussion Starter · #3 ·
Just to remain consistent, same fuel was used? Relatively same conditions during testing?

Those corrections are very similar so pretty small differences could have caused the corrections to vary, however I'm all ears for any other input from someone. I've never had issues with my open ended filter, but also see regular -1.72ish corrections with current setup and fuel.
Yes to all of the above. Same tank of gas. Same type of conditions and roads. FWIW I'm running a Mountune 91 octane tune.
 

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The sound of the open filter comes from within the system anyway, so unless I'm missing something that is not so likely. It's probably more due to the intake temps rising while sitting still because of stale engine bay air, then lowering more than usual when moving due to the air flow through the bay.
 

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Discussion Starter · #5 ·
The sound of the open filter comes from within the system anyway, so unless I'm missing something that is not so likely. It's probably more due to the intake temps rising while sitting still because of stale engine bay air, then lowering more than usual when moving due to the air flow through the bay.
I would be hesitant to not believe the sound waves going through the system are different when something is muffled vs. not. Think about drone that can be created when an exhaust resonator is removed. Wasn't sitting still. Pretty much highway. I also understand there isn't any difference between intake temps when moving and minimal differences when standing still.
 

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I would be hesitant to not believe the sound waves going through the system are different when something is muffled vs. not. Think about drone that can be created when an exhaust resonator is removed. Wasn't sitting still. Pretty much highway. I also understand there isn't any difference between intake temps when moving and minimal differences when standing still.
I agree that others have found only small differences open vs closed. But I must argue that the differences you have seen are also small. I see slightly different ignition corrections from one day to the next using the same fuel and same atmospheric conditions. You've also swapped the intake tube, which could have caused the ECU to see a change and subsequently calibrate. As for the drone argument, I'm a bit confused where you are trying to go with that. Changing the exhaust can cause drone, but I've never heard of it causing false knock. Anyway, not trying to be condescending or anything. Just playing the devil's advocate here. Congrats on the new intake, maybe I'm just a little jealous :haha:
 

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Discussion Starter · #7 ·
As for the drone argument, I'm a bit confused where you are trying to go with that. Changing the exhaust can cause drone, but I've never heard of it causing false knock. Anyway, not trying to be condescending or anything. Just playing the devil's advocate here. Congrats on the new intake, maybe I'm just a little jealous :haha:
No worries. I'm not taking it as condescending. I'm not saying the drone from removing the resonator (or changing exhaust) causes false knock. I'm just giving an example of how the sound waves change. Would anything that happens post engine cause false knock?
 

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Not sure, I suppose if an impulse is redirected toward the engine, the sensors could detect some sound. But if that were the case, the stock exhaust would cause false knock, because from my understanding it functions by reversing the sound waves. Intuitively, one would believe that the sound wave would exit through the open ended filter, and therefor having the end closed would reverberate the sound wave and cause false knock. These are guesses though, I'm no scientition ¯\_(ツ)_/¯
 

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