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Performance gain from removing MAF screens?

8K views 22 replies 10 participants last post by  1994v12 
#1 ·
Hey guys,

So I was searching around the internet looking for ways to further improve my 600SEL (a never-ending quest by the way [emoji23]) and I did some research on the Bosch LH Jetronic system and I found this interesting bit of information in a book called "How to Tune and Modify Bosch Fuel Injection" By Ben Watson.

So according to this information, cutting away the screens on the MAF sensors will apparently increase airflow which makes sense. And from my understanding doesn't increased airflow essentially equal better performance? My question is, is there really gonna be a noticeable difference that makes it worth the effort and also will it be safe for the engine? I understand the point of these screens is to keep debris from entering the air supply to the engine but shouldn't the air filters that come BEFORE the MAF sensors take care of any sort of potential debris entering the air supply? I'm not trying to take some sort of shortcut here or anything to make my car go faster or anything like that, but if it works and wouldn't be detrimental to the car it seems like another little thing worth doing to the car. It seems like people have had success with this on other Mercedes models particularly the R170 SLK but I wanted to get your guys' input on this first for our model before I go doing stuff that I don't know what the end result of which will be. Any help is appreciated.
 
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#2 ·
Hmm, interesting. My first instinct would be to say there's no way the screens could make any difference, but I guess there's something to the idea.

The author said the increase in airflow would be 'considerable', which implies a performance increase (more air means more power, generally). But I have no idea what the gain would turn out to be in a practical sense. I still have a hard time believing the screens make that much difference.

Also, the screen is your last line of defense against debris getting sucked into the engine. Chances are your airbox/filter is up to the task, but is the small risk worth the extra couple of HP? I mean, maybe it is, but I'd want to know for sure that the increase in airflow was gong to do give at least another 5 or more horsepower.
 
#5 · (Edited)
Hmm, interesting. My first instinct would be to say there's no way the screens could make any difference, but I guess there's something to the idea.

The author said the increase in airflow would be 'considerable', which implies a performance increase (more air means more power, generally). But I have no idea what the gain would turn out to be in a practical sense. I still have a hard time believing the screens make that much difference.
Your gut feeling is probably correct. There are many *authors* out there that claim that "special" air-filters or that the DTM-style exhaust tips for example can also lead to significant increase in power.
But, and this is a big BUT, there are no dyno-results to substantiate any of those claims. It is all based on the amount of noise produced (or another completely subjective criterion).

My 2 cents -- to make gains in the power department, one needs more than that. Read -- more $$$.

Best regards,
Steve
 
#3 ·
From the information I've found its not necessarily the amount of air that is increased but the air flow would be more direct. Apparently the screens are a cause of substantial turbulence in the air, and removing them will allow the air to just blast through to the engine. The million dollar question of course is how much of a gain will this really provide if any

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#8 ·
Visually the M120 intakes have trumpets each side with smaller x-section than the mafs with the mesh.

I'd think the AFM mesh stabilizes and evens the airflow for more accurate AFM reading.
 
#9 · (Edited)
I read about this about 5 years ago, and was intrigued. So, I removed the protective screen on my MAF in my 2000 Volvo V70R. My though, just like yours, is that the air filter will do its job and catch anything that would be big enough to do any harm to the MAF or the Turbo, which is next in line. And, to this day, that car still has no screen on the MAF, with no ill side effects or anything getting past the air filter.

NOW, as far as any performance increases: I cannot say. Mostly because the car I tried it on has a turbo, and a very short intake (from inlet, though the air filter and MAF, to inlet of the turbo is shorter than the length of my arm), and only has two soft 60 degree bends; so there really isn't enough time for turbulence to effect the incoming air flow.
But, I can tell you this though: a MAF's job is to meter the amount of air that is flowing into the engine, and adjust the air/fuel mixture accordingly. So, if larger than normal amounts of air were to enter the system due to the removal of the protective screen; the MAF would compensate by for it by adjusting the fuel mixture down to cause normal levels of combustion. Thereby negating any benefit from the removal of the screen. So, will it increase performance by increasing air VOLUME? No.

But, when you look at air FLOW, it's a different story:
The less turbulent air is when flowing though pipes, the less pressure, or compression, it has. When talking about getting air into a normally aspirated engine, this is ideal. Because, the less resistance, the more it flows; the more it flows, more of it can end up in the cylinders. So, can it improve performance? I think yes.
With a NA engine that has long intake tubing, every turn and twist matters. Everything that is inserted into the flow causes turbulence. So, a protective screen that spans the diameter of the pipe... yeah, that's gonna cause some. And it will matter down the line when the turbulent air gets divided up and enters the cylinders.
I will say this though: when I redesign the intake piping for my M120, I will be taking the protective screens off the MAF sensors.
 
#20 ·
But, I can tell you this though: a MAF's job is to meter the amount of air that is flowing into the engine, and adjust the air/fuel mixture accordingly. So, if larger than normal amounts of air were to enter the system due to the removal of the protective screen; the MAF would compensate by for it by adjusting the fuel mixture down to cause normal levels of combustion. Thereby negating any benefit from the removal of the screen. So, will it increase performance by increasing air VOLUME? No.

But, when you look at air FLOW, it's a different story:
The less turbulent air is when flowing though pipes, the less pressure, or compression, it has. When talking about getting air into a normally aspirated engine, this is ideal. Because, the less resistance, the more it flows; the more it flows, more of it can end up in the cylinders. So, can it improve performance? I think yes.
With a NA engine that has long intake tubing, every turn and twist matters. Everything that is inserted into the flow causes turbulence. So, a protective screen that spans the diameter of the pipe... yeah, that's gonna cause some. And it will matter down the line when the turbulent air gets divided up and enters the cylinders.
I will say this though: when I redesign the intake piping for my M120, I will be taking the protective screens off the MAF sensors.
the statement above is an error, and misconception. if the MAF senses a larger volume of air entering the engine, IT ADDS FUEL to match that throttle opening flow while driving ! it doesn't "adjust the fuel mixture down", it adjusts it UP !!
the MAF is there to measure the amount of incoming air, and add the appropriate amount of fuel to it. nothing more. the poster did not understand the way the OBD system works. if the MAF senses more air, it tells the computer add more fuel, which the computer then does. it's a loop, input sensor/output fuel injector system, with the ECM using the sensor inputs, to adjust the outputs. same thing with the MAP sensor in speed density mode, it's sensing load based on vacuum reading in the intake manifold. when vacuum drops, and the throttle valve is being opened, it adds fuel.
when you buy a "performance" MAF sensor, you get one that will do 2 things, sense a higher level of airflow at maximum high end, and starts off being richer from the get go. in other words, instead of it starting out at 0 on a scale of 0-10, it starts out at 1. so it's richer across the entire range by an increment or 2. that's how the aftermarket MAF tricks the computer into dumping more fuel than it should, to get more HP out of the engine. and it's all done with resistance and voltage/amperage readings, and temp readings.
 
#10 ·
Yes I agree that it seems to be not a matter of air volume but rather air flow. However there seems to be two opposing opinions forming on this topic. It seems that some believe that the screen helps combat the turbulence of incoming air, while others believe that the screen is the actual source of turbulence. I guess perhaps further research or a little testing might provide an answer as to which theory is correct

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#11 ·
Back in my Buick Grand National days this exact topic was covered. People felt they where getting all this additional power by removing the screen...others felt it was useless. I think the consensus was that some guys that worked for GM stated not to remove it as the screen does something to smooth or straighten the air flow/path and makes the sensor more stable on it's readings.
I think that was the bit of it; don't recall to much of the specifics. I say just leave them in, big deal. Unless your really bored and want to experiment find another set of MAF's and remove the screen and swap them in, then find a dyno.

Chris
 
#18 ·
from the 3.8 GM site:

The stock Throttle Body can be restrictive even on a stock engine. The factory installs a screen in the inlet of the Throttle Body to straighten the air as it travels into the MAF sensor. This provides a smoother idle and more consistent fuel delivery. For Maximum performance this screen is disruption in the airflow that can be removed with little or *no adverse effects. On the flow bench we have realized a 10-15% increase in airflow by removing the screen.
 
#19 · (Edited)
better yet, remove the entire MAF, get maximum airflow from the cross sectional area, and run the car on speed density system. one screen is kept in place, for all-out runs when air filters are pulled. performance increase ? substantial on the V12 engine. the M120 in stock form was hampered considerably by restrictive, lean burning emissions/engine controls, and intake/exhaust impediments. stay tuned as the intake tract is further improved, the next step is so simple, it's hiding in plain view.

2644122
 
#22 ·
Stay tuned as the intake tract is further improved, the next step is so simple, it's hiding in plain view.

View attachment 2644122
If you really want to address intake tract restriction, get rid of the ribbed factory elbows and use smooth hoses everywhere that you can. Gutting a MAF while leaving the actual sources of drag in the intake tract is chasing a rolling penny while ignoring the dollar bill floating by.
 
#21 · (Edited)
Let's look at that statement:
"So, if larger than normal amounts of air were to enter the system due to the removal of the protective screen; the MAF would compensate by for it by adjusting the fuel mixture down to cause normal levels of combustion."

If more air than normal enters the system for a specific amount of fuel the air/fuel ratio is higher than normal; let's say it should be 14.7 but now is 15.3. By measuring the amount of air (the screens are designed to ensure accuracy) and adding fuel, the ECU adjusts the air/fuel mixture back down to 14.7.

Adjustable MAFs were used to trick the ECU but aren't needed or desired with systems that can be tuned.

The dyno operator that I use really likes MAF systems because they can be tuned so much easier than a speed density system. Without a MAF to measure the actual airflow, lots of assumptions and fiddling have to be made to get the VE table right over the full range of engine performance; with a MAF, the response curve is tweaked to get the desired result.

Also a speed density system needs to be retuned after each significant mod whereas the MAF system just does what it does by measuring the actual airflow; no retuning required.

So little to be gained by a speed density system over a MAF and so much to be lost.
 
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