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Discussion Starter #1 (Edited)
All,

I tend to get a bit wordy so I'll try and keep it brief. Being in California, we can not "legally" use a SRI. In addition there are many that feel like the OEM airbox can provide plenty of air and does a better job because it uses a snorkel to pull cold air from the outside. So I got an idea on how to test flow as a comparison... THIS IS NOT A MAX FLOW TEST, but a comparison that I am very satisfied with and I hope will help others maybe finally answer some age old questions.


Disclosure... Guess I should mention this is done with an OEM airbox from a 2017 Mazda 3 (2.5 L).. however I also have a 2013 Mazda CX5 (2.0 Liter) and it uses the same air box.


So lets get to it.. the setup was simple once I got the idea. Basically I used a Volt meter, a computer Case Fan, and a shop vac. Keep in mind that the shop vac pulls no-where near the CFM that the engine needs (half at most) which makes this test even more interesting because it means my results would be amplified!


Setup

This is the setup. As you can see I have detached the intake tube from the Throttle body and inserted my shop vac. I have sealed the PCV tube and the blue rag you see is just to help seal around the vacuum tip. In addition, you will see I have placed the Case fan at the snorkel entrance.


Dirty OEM Filter

This is an OEM filter that was taken out of my CX5 with around 20-25k miles on it. It produced 2.39 volts.


Clean OEM Filter

This is an OEM filter that was taken out of my new Mazda 3 with around 1k miles on it. It produced 2.47 volts.


AFE Filter (Pro Dry S)

This is my brand new AFE Pro Dry S filter. It produced 2.50 volts.


NO Filter

This is with No Filter. I did hold down the lid to get the best seal I could. It produced 2.25 volts. I was surprised that it was lower than any of the "with filter" combinations. But the number doesn't lie and I did it multiple times... educated guess.. no filter = more air turbulence.



Now for the Great Debate over the Charcoal filter....


For those that do NOT have PZEV cars, this won't apply. But for those that do, this is a charcoal filter that is welded into the top half of the air box used to capture fuel vapors when the car is shut off. Huge debate over this.

Referencing the "No Filter" output of 2.25 volts, I then cut out my Charcoal filter and retested... as you can see the voltage went up to 2.32. That is a 3% increase (again..keep in mind my Shop vac doesn't pull like the engine).

Now to really hit this one home, once I was all done with the Air box, I did one more additional test to prove the potential restriction of this Filter....


Charcoal Before Test

This is the fan sitting right on top of the shop vac. As you can see it can pull 5.0 volts without having to go through all the tubing of the OEM box.



Charcoal After Test

Now I inserted the filter in between. I had to hold the edge to keep the filter flush with the fan so it could not pull extra "unregistered air". As you can see the voltage dropped down to 2.76. That is a -45%

Now I know people are going to be up and arms about this.. but the question I was trying to answer was not how much HP is this taken but the simple argument where many have claimed, the charcoal provides no restrictions what so ever... well I don't agree.

I will give it this however.... If I'm standing in a room with an open window, and someone shuts the window... that DOES provide a restriction. However will I be starving for air.. I think not. So take it for what it's worth.


End the Great Debate over the Charcoal filter....





Summary


So to repeat, this wasn't about MAX flow, or whether or not even at the lowest flow numbers, our engines would be starving for air (standing in a room with a window open or closed idea). It simply was to compare various filter and flow using the stock air box.

So to simplify it ...

No filter = 2.25
Dirty filter = 2.39
Clean filter = 2.47
AFE filter = 2.50

So using the Clean OEM as the base...

No filter = -9%
Dirty filter = -3%
Clean filter = 0%
AFE filter = 1%


Note: I hope people don't take this test out of context and start posting everywhere that a performance air filter only increases flow by 1% or that there is no need to change your filter because it only reduces flow by -3% .... Remember, this is shop vac numbers and not real world dynos on an actual engine!

As a side note, I did compare the AFE to the stock OEM (clean) using the same method as the Charcoal filter and the AFE at a concentrated point did actually flow 19% more. So I believe that the potential is there to get more air, just don't know if our engines can make use of it.


So the only question left remaining (at least to me) is what would these really look like if I could have a shop vacuum that pulled 300 CFM like our engine.
 

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Discussion Starter #2
Side note, just had my cx5 oil tested and had higher silicone numbers. Interesting because I was running an oem filter (unless it was a forgery).

Will have to keep an eye on the new car with the AFE ... seems like 99.2% should be about as good as it gets unless oem is 99.9% :)
 

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Very good read.
 

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wow..I made sticky!

As a side note, I'm about to get the OV tune so I'll be pulling some real numbers with this stock setup and the AFE.

Should come out if I'm dealing with an Air restriction.
 

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Nice test and results. I really wish you would have used something that had MORE flow then our engine to really see the difference in restriction. I'm sure the numbers between the dirty filter vs new would be much more dramatic because common sense dictates that a dirty clogged filter will flow worse then a fresh one.

I have to agree that on a stock engine, the OEM air box probably offers all the air that it needs, unless Mazda made it smaller and more restrictive ON PURPOSE in order to limit the horsepower (one of many methods they use to achieve LESS power) if needed.

Once people start modifying the engine to produce more power with say a full exhaust system with a performance header, cams, bigger intake manifold and throttle body, etc then obviously the OEM box will be a huge restriction at that point but on a stock block with an axle back exhaust and not even a tune to make full use of it... I agree that the OEM airbox performs best, especially in a hot climate with the AC running and idling in traffic where engine bay temps sky rocket and the engine suffers from massive heat soak.

Nicely done test nontheless though. Thanks for the effort.
 

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Discussion Starter #9
I tried to figure out how to get more CFM. Best I could come up with was for about $100, I discovered that there are some combo leave blower/vacuums that put out some decent levels of CFM that exceed what our engines could ever possibly pull.

Rereading my post I mentioned my tune. During my test IIRC my MAF was in the high 130's and think I may have even got up to 148 on some runs.
 

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This is very interesting. I wonder if this could be used to test the Stock air box vs the Corksport airbox.
 

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I tried to figure out how to get more CFM. Best I could come up with was for about $100, I discovered that there are some combo leave blower/vacuums that put out some decent levels of CFM that exceed what our engines could ever possibly pull.

Rereading my post I mentioned my tune. During my test IIRC my MAF was in the high 130's and think I may have even got up to 148 on some runs.
Relating MAF sensor reading to CFM numbers can be quite misleading. CFM is just volume of air, MAF is temperature dependent. With the same CFM you can get a range of MAF numbers according to the density of the air, which is dependent on temperature.


This is very interesting. I wonder if this could be used to test the Stock air box vs the Corksport airbox.
I would not worry about the CS airbox too much. It seems to flow just fine compared to stock. What you should be worrying more about is controlling intake temps. Reducing intake temps is the best way to increase the mass air flow. It does not make a difference how large the volume of air available to the engine is. A naturally aspirated engine is an air pump and as such is limited by the mechanical processes. Only so much air volume can be moved at any given point in time. So, increasing the density of that volume is the best way to increase the fuel/air intake.
 

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Grab a magnehelic gauge (these are sensitive vacuum gauges), drill a small hole into intake pipe just before T/B.
Insert a small nozzle (from garden watering section of hardware store and and also get 8-10ft of rubber clear hose) into into hose and then insert into intake tube hole.
Run hose into car (mindful not to pinch it), connect to gauge, carry out your tests (dirty/new/no filter etc)
Less vacuum = less restriction. Plug the hole you drill with a rubber plug or a dab of black RTV sealant. You can move the nozzle to different sections and find an actual restriction point (ie snorkel or airbox base or lid or lid exit tube etc)

Similar for IAT but a cheap chinese LCD temp gauge will do.
Simple but precise.
 

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Grab a magnehelic gauge (these are sensitive vacuum gauges),
Similar for IAT but a cheap chinese LCD temp gauge will do.
Simple but precise.
:punk:
This is a fun thread and some good DIY "check out the info" on an airbox.

INRW (In The Real World) it is not as easy as simply measuring one aspect of any airbox,filter or CAI. The internet is full of claims but the bucks stops when one can use proper measuring devices and confirming everything on either/or an Engine and/or Chassis DYNO with the correct DELTA set (somebody that knows their DYNO and the operating program)for the test.
Over the years I have found some better personally established conclusions (The 5 Step problem solving approach) of information other then what I read at times on the internet. :nerd:

20180127_141144_resize.jpg

20180127_141153_resize.jpg

As for IAT's and other operating temperatures I use an Ultra Gauge to keep watch of most common ones and if I do go heavy on the engine performance modding I will also include oil, transmission fluid and EGT's among other's monitored.
 

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can anyone tell me the diameter of the inlet (to the MAF) in the airbox lid?
 
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