Air Filter Placement

ctuinstra

Goblin Guru
Lesson learned. Be careful how you place your air filter. During our build, I thought that it would be a good idea to keep it up in the surrounding air and away from any engine heat. It was standing almost straight up. Well, during tuning of the MAF tables, I was out collecting logging data and when a gust of cross wind would come, it would blow the AFR off the charts! During slower driving and no wind, they would be right were the should be. I couldn't even get a few miles before returning home.

I still had the 45 degree 3" silicone provided by DF that I never used. I repositioned in down behind the driver's seat and below the coolant tank. Took the car back out and never had a problem! AFR were spot on all the time. The difference is incredible! When running on the MAF alone, it would darn near kill the engine with a huge gust of wind. I guess running normally with dynamic airflow (using the MAF and VE tables to calculate) it would not affect it as much, but I'm sure it still did.

This is what I used to have.

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This is the set up most have and what I changed to:

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This is with the original set up. AFR Cmd is what the ECM is wanting and "commanding". The WB AEM is the actual AFR coming out of the tail pipe. Keep in mind, this is only running using the MAF sensor to control the fueling, nothing else (basically).

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This is just moving it, no other changes to the car or tuning!

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Lesson learned. Credit to my dyno tuner, last year he said the air filter was in a bad spot. Now I believe him.
 

Ross

Goblin Guru
The morning of the last autocross, I noticed my red air filter was missing. Guess it fell off when I was driving.
The MAF didn't like the missing air filter, and I lost power at high RPM, and sometimes had a rough idle.
Today I put a new filter on, and added a 90 degree aluminum pipe, to try and make laminar air flow thru the MAF.
22516


It runs great, and I hear the supercharger a lot more!
22517
 

TheNuker

Goblin Guru
The morning of the last autocross, I noticed my red air filter was missing. Guess it fell off when I was driving.
The MAF didn't like the missing air filter, and I lost power at high RPM, and sometimes had a rough idle.
Today I put a new filter on, and added a 90 degree aluminum pipe, to try and make laminar air flow thru the MAF.
View attachment 22516

It runs great, and I hear the supercharger a lot more!
View attachment 22517
Yeah that SC is almost ear piercing at 7k!
Nuker-
 

Ross

Goblin Guru
Tomorrow I will try this Atom arrangement.
22519


I want the passenger to enjoy the music too.
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If I was willing to cut the pipes, I could get a better routing, but I will try and see.
 

Gtstorey

Goblin Guru
Hopefully mine is closer to Ross's first post than Chad's, although I'm a little worried about the lack of laminar flow. The MAF hasn't changed from where it cam on the K&N intake but I would fill better with a little more straight pipe.
22691
 

ctuinstra

Goblin Guru
I’m telling you, I’m a believer now that the filter needs isolation and out if direct wind.

Just this weekend while at the Autocross, Kaleb said while sitting there waiting to go a gust of wind would come up and blow against the side of the car and darn near kill it while idling. This is even after moving it down, it’s still open to the side. And then while in the course making a hard right turn, a gust from the left side caused a bog. I’m going to cover the side with some tinted acrylic.
 

Ross

Goblin Guru
They recommend 2 x diameter of straight tube both before and after the MAF. On our 3" intake, that is 6" before and after. Both Chad, Gtstorey and the stock DF arrangement are missing the 6" straight before the MAF... so stretching the filter as far away from the MAF before tightening the hose clamp, is important. Better yet, buy some pipe, and put it where you want:
- 3.0" Silicone Straight Coupler, Blue (SIL000604) $7
- 1' Straight Aluminum Pipe, 3.0" $10
 

Gtstorey

Goblin Guru
K&N increases the tube size to 3.25 for the short section where the MAF is mounted and obviously no straight section after the MAF. All of this is going to likely add up to something that may be hard to tune and I may go back to the stock DF location or modify what I have now. The first option I will likely try is a honeycomb insert to try and straighten the air.

3.25 OD x .5 Airflow Straightener Screen .187 honeycomb cell mass air flow | eBay

Upon further thought, I'm wondering if Chad's problems might not also be the short length at the MAF causing disturbed airflow with heavy winds, and the relocation just makes it more stable. I don't think the air pressure increase from the wind alone would cause the problem.
 
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ctuinstra

Goblin Guru
They recommend 2 x diameter of straight tube both before and after the MAF. On our 3" intake, that is 6" before and after. Both Chad, Gtstorey and the stock DF arrangement are missing the 6" straight before the MAF... so stretching the filter as far away from the MAF before tightening the hose clamp, is important. Better yet, buy some pipe, and put it where you want:
- 3.0" Silicone Straight Coupler, Blue (SIL000604) $7
- 1' Straight Aluminum Pipe, 3.0" $10
I agree that the straight sections are a good idea. And I’m sure they would be less impacted by wind. Surprisingly OEM doesn’t really follow this rule in many cases, or even close. Not sure why.
 

ctuinstra

Goblin Guru
Upon further thought, I'm wondering if Chad's problems might not also be the short length at the MAF causing disturbed airflow with heavy winds, and the relocation just makes it more stable. I don't think the air pressure increase from the wind alone would cause the problem.
Without a doubt the shorter pipe to between the MAF and filter is making it more susceptible to the disturbance of air. It’s a trade-off between the longer pipes and their real estate and the shorter pipes and placement. That’s probably how the OEM is able to get away with short flows. I wish I had a photo of the recent set up I saw. I remember thinking that the manufacturer didn’t design a pipe any longer than what I have.
 

Gtstorey

Goblin Guru
I agree that the straight sections are a good idea. And I’m sure they would be less impacted by wind. Surprisingly OEM doesn’t really follow this rule in many cases, or even close. Not sure why.
Another thought is was your maf tune set up for the first location? Your graphs looks to me more like it was actually moving more air than it though and causing it to run lean. The new location may have been closer to the Cobalt set up and thus ran better. Or maybe it's just wishful thinking on part to not have to move mine.
 

Desert Sasqwatch

Goblin Guru
I agree that the straight sections are a good idea. And I’m sure they would be less impacted by wind. Surprisingly OEM doesn’t really follow this rule in many cases, or even close. Not sure why.
I believe a big factor is the factory filter box that virtually eliminated having a breeze blow across the filter and causing rapid changes in incoming air flow/density, by having everything tucked under the hood.
 

ctuinstra

Goblin Guru
Another thought is was your maf tune set up for the first location? Your graphs looks to me more like it was actually moving more air than it though and causing it to run lean. The new location may have been closer to the Cobalt set up and thus ran better. Or maybe it's just wishful thinking on part to not have to move mine.
The tune was from the first location and then after moving it, I re-tuned it. The changes were very subtle and negligible. I don’t think the position really changed the tune as much as the wind was not screwing with the tuning process.
 

Gtstorey

Goblin Guru
The tune was from the first location and then after moving it, I re-tuned it. The changes were very subtle and negligible. I don’t think the position really changed the tune as much as the wind was not screwing with the tuning process.
What's the horz. scale of your graphs above? Was that a few seconds or a few minutes?
 

Gtstorey

Goblin Guru
The logging snippet was about 10-20 seconds long.
How about throttle/RPM? I assume that's light throttle/cruise since command ratio is 14+. 18:1 is LEAN and it looks like that might just be as high as the sensor can read since it's clipped off exactly at the same point.
 

ctuinstra

Goblin Guru
How about throttle/RPM? I assume that's light throttle/cruise since command ratio is 14+. 18:1 is LEAN and it looks like that might just be as high as the sensor can read since it's clipped off exactly at the same point.
I’ll include more of the scan log when I get home. I should have but figured it might be less overwhelming to some if I keep it simple.
 

ctuinstra

Goblin Guru
I tried to get close to doing a screen capture of the same area of the log, but this time include the time stamp and all of the other logging. You can see my speed was steady, the throttle (TPS) was mostly steady. You can't really see the MAF move with this because it's scaled so low but increasing the scale does show it move.

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I'll include both files, the before and after. The trip wasn't the same so the will not be a direct comparison, but you can see trends and how it reacts. 0034 is the before and 0037 is the after. No changes to anything other than the position of the air filter.
 

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