Tech Tips
MAF Screen Removal
One Word ~ DON'T

 
Let me start by saying this article is a combination of research available on the internet, my humble opinion, and the following of hundreds of tech post regarding MAF Screen Removal. 
 
A few years ago Hot Rod Magazine ran an article on the proposed horsepower gain that could be had for free by the removal of the front and rear MAF Screens. Adding to the resulting screen removal frenzy are companies like TPIS that offer the service of removing the screens and "gutting" the fins, again, for a reported HP gain.
 
The most critical note to be realized (that most don't) is that the engines that these were being used on were heavily modified.
 
The Myth: Across the internet and word of mouth spread the news of this "free mod" and countless pages promoted the technique of MAF Screen Removal without considering some very basic theories and the potential harm of doing this mod. Consequently time after time you will see the post and topics "I removed my screens - now Code 33".
 

The Fact: The MAF Screen Removal Process WILL NOT CREATE horsepower within itself. It can only in the right conditions FREE UP horsepower that ALREADY EXIST and only under certain conditions.

Why?

1. Your stock MAF with screens will outflow your stock 48mm throttle body.
2. It will even outflow a 52mm throttle body.
3. It will also outflow your stock intake.

 
This Means: that if you are still using these stock components your MAF screen removal process is totally wasted and potentially (code 33) dangerous and could cost $100.00 + if you screw it up. The MAF has to be the most restrictive element in your chain of flow to even possibly make the mod worth anything and ONLY if you already have the horsepower to free up by a modified throttle body and intake.
 

Why the Screens?

 
What kicks me in the pants is not only do I personally feel that these screens are the single most important part of the MAF but that they serve multiple purposes. The screen in the front filters potential debris, prevents something from being dropped into the MAF when working on car, a tool slipping, etc., and the rear screen not only serves the same protective service but it also helps cushion potential damages to the fragile MAF wire that can be caused by a backfire under lean conditions. And these services are secondary to their primary purpose which is to regulate airflow for measuring purposes.
 

Are the Screens Restrictive?

 
Absolutely they are, but by design. Is your voltage regulator restrictive? Is your air cleaner restrictive? Is your fuel filter restrictive? Are your fuel injectors restrictive? Is your fuel pressure regulator restrictive? Yes they are.....by design. Would you remove your air cleaner or fuel filter? We are blessed with the common sense that although restrictive we find these components necessary for proper operation and to remove them would be foolish or asking for trouble. It is very unfortunate that we don't possess the same common sense regarding the MAF sensor.
 

Theory of Operation

 
Understand two terms first of all. Turbulent Airflow and Laminar Airflow. They are opposites. Without definition we can identify with "turbulent" but "laminar" airflow would define as "smooth, straightened out, regulated".
 
To help understand some conflicting articles I will point out an important factor here right away. There is no such thing as turbulence free airflow. Airflow is a "fluid flow" and a fluid flowing past obstructions, against boundaries, even the composition of the fluid itself in different densities and pressures create turbulence that can't be removed. So when we speak of Laminar Airflow being smoothed out and being the opposite of turbulent airflow we're speaking of a "controlled turbulence" vs. "uncontrolled turbulence".
 
Envision this process by thinking of your kitchen faucet. The little screen on the end. Take it out and watch your water flow increase but also notice it splash around and surge. You can see the uneven flow very easily. Put the aerator back in and see it smooth out in a more regulated even flow. Look at the end of most hair dryers and they will have a screen in them. Of course this is to prevent getting your hair sucked up in there and catching your head on fire BUT it also disperses the air in a more even, regulated pattern. Think of the construction of a dam on a river. You KNOW it is restrictive. It "holds back" the natural flow of water and regulates it to a desired given amount. Why? To do something productive with the process of flow. Just like your MAF screens.
 

The MAF Process

 
I am going to chop this section down to the most basic of processes. GM didn't invent this process, as a matter of fact it is the same process used by the weather industry to measure "chill factor" so it's theory was utilized by GM not invented by them.
 
1. You have a small wire inside your MAF which can be heated.
2. It is calibrated at zero airflow to be a certain temperature.
3. Air flowing across the wire cools it off. The more air flow the cooler the wire.
4. A voltage is supplied to that wire to keep it at a constant temperature. The more air flowing, the cooler the wire, the more voltage required to keep it the same temp.
5. This voltage fluctuation is a measurable, readable function which when converted to a digital output can be used for calibrations of airflow entering your intake.
6. These calibrations are referenced to a lookup table stored in your ECM and based on these fluctuations various functions of your engine are controlled based on the amount of airflow you are encountering.
 
The screens are there simply to provide a steady, stable, regulated environment for the most precise calculations available.
 
Now I will point you back to one of my previous "goofy-assed" examples and ask: Would it be easier to count the number of gallons that flow past a certain point in the river ...with the dam or without it? That is what your screens are for... to establish "near as possible" level playing field ground zero reference point for calibrations.
 

What Happens When They are Removed

 
Without the screen, the computer can not take a correct reading on how much air is entering the engine. When you port the MAF housing and/or remove the screens you are causing air to move by the sensors that is not being measured. Lower frequency outputs are being read by the lookup charts and the calculations are based on lower than actual airflow.

This makes the ECM lean out the fuel mixture and add timing. Then the oxygen sensors read the lean fuel mixture and bump it back up to compensate for the MAF sensors low readings.
 
In Summary I would say that I have heard of people making this mod and not having trouble codes. I have also heard of reported gains in performance. In both of these situations, if true, you have my respect and congratulations but I have never seen proof of these gains especially on a stock setup. I have however lost count of the number of post that are encountering trouble after making this "free" mod. Further I would say that if the horsepower is not there in the first place your sure not going to create any new horsepower cutting out your screens.
 
The MAF is a truly unique and awesome device that allows us to drive in different environments (altitudes) with no intake modifications. Allows us to make "other" performance mods without having to calibrate a new PROM. To butcher it and make it less accurate and precise just doesn't make sense to me.
 
1. If you are driving a stock intake car this mod will do absolutely nothing for you.
2. If you have such a heavily modified engine that it would make a difference Why are you using the MAF system anyway? .....you should be on Speed Density with a custom chip.
 
My personal disclaimer is this. If you have already cut your screens out I am not saying your stupid or you did something bad. I am saying that maybe you were misinformed or that there was a lack of information available to make the best possible decision for your situation. This article is not to point out mistakes, make fun of, or even say "I'm right ~ you're wrong". But merely to present an opposing view, a difference of opinion, and possibly a closer understanding of a mysterious, complex component.
 
 

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