MAF Screen
03-18-2005, 08:43 AM
#23
I would leave the screen in. I have seen a lot of crap somehow get sucked in tho the intake and stuck to the MAF screen. mostly leaves and other plant products. These are on everyday passenger cars that are bone stock.
If you want to take the screen out, there is a big snap ring outside the screen. Take the ring out and use a small pick to pull the screen out. very easy and no need to buy another MAF.
If you want to take the screen out, there is a big snap ring outside the screen. Take the ring out and use a small pick to pull the screen out. very easy and no need to buy another MAF.
03-18-2005, 09:50 AM
#24
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It seems that people believe the screen is meant to "straighten" the airflow through the MAF, but it would appear that the divider behind the filament is meant to do just that. Which probably explains the reason why everyone complains about the ported ends.
Just speculating. I haven't had the opportunity to test different scenarios with data loggers and tuning software. Maybe someone who has tuned a lot of cars and has seen different test cases will chime in...
Just speculating. I haven't had the opportunity to test different scenarios with data loggers and tuning software. Maybe someone who has tuned a lot of cars and has seen different test cases will chime in...
03-18-2005, 10:02 AM
#25
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I measured this all right back when I got my car. Not
at all calibrated, but using the same shop vac source
and measuring the vacuum level in the can, the stock
lid produced about 1/4"H2O drop, so did the screened MAF,
and the paper filters were well less. I expect the flow was
a small fraction of what the motor draws; don't concentrate
on the absolute numbers, just their relative weight.
Oh, and those ball-lickers over at WebShots dumped all my
photo howto albums, so don't bother following that link in
this thread:
https://ls1tech.com/forums/generation-iii-external-engine/70694-lid-o-rama-data.html
at all calibrated, but using the same shop vac source
and measuring the vacuum level in the can, the stock
lid produced about 1/4"H2O drop, so did the screened MAF,
and the paper filters were well less. I expect the flow was
a small fraction of what the motor draws; don't concentrate
on the absolute numbers, just their relative weight.
Oh, and those ball-lickers over at WebShots dumped all my
photo howto albums, so don't bother following that link in
this thread:
https://ls1tech.com/forums/generation-iii-external-engine/70694-lid-o-rama-data.html
03-18-2005, 01:30 PM
#26
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Fluid Dynamics 101
Originally Posted by technical
It seems that people believe the screen is meant to "straighten" the airflow through the MAF, but it would appear that the divider behind the filament is meant to do just that. Which probably explains the reason why everyone complains about the ported ends.
Screen increases small scale turbulence resulting in a flater velocity profile.
+ easier to calibrate MAF (less variability)
- increased pressure drop (lower mass flow efficiency AKA VE)
Sketched in 30 seconds
03-18-2005, 01:47 PM
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Well, first off I descreened my car and noticed a tiny difference. But I put a K&N on at the same time.
From an engineering perspective the screen is made to straighten out airflow as others have stated before. It IS needed on some vehicles with curved intakes (i.e. trucks and some other cars). However, on vettes and F-bodys the intake is pretty much straight, so you can get by without it. On the 02 Z06 and up GM eliminated the screen completely.
Descreening definitely will increase airflow compared to having it in. Air is a fluid. It experiences friction when flowing over something not moving. So all those little holes in the screen create lots of friction with the air passing by. In the case of a cylinder, the fastest point of fluid flow is in the center of the cylinder. As you move from the center out towards the walls the velocity of the air decreases and eventually reaches 0 at the wall of the cylinder; due to friction. So with the screen in you basically have all those little cylinders versus having one big cylinder with the screen out.
From an engineering perspective the screen is made to straighten out airflow as others have stated before. It IS needed on some vehicles with curved intakes (i.e. trucks and some other cars). However, on vettes and F-bodys the intake is pretty much straight, so you can get by without it. On the 02 Z06 and up GM eliminated the screen completely.
Descreening definitely will increase airflow compared to having it in. Air is a fluid. It experiences friction when flowing over something not moving. So all those little holes in the screen create lots of friction with the air passing by. In the case of a cylinder, the fastest point of fluid flow is in the center of the cylinder. As you move from the center out towards the walls the velocity of the air decreases and eventually reaches 0 at the wall of the cylinder; due to friction. So with the screen in you basically have all those little cylinders versus having one big cylinder with the screen out.
03-18-2005, 02:11 PM
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Fluid dynamics 201
Originally Posted by SSpeedracer
Screen increases small scale turbulence resulting in a flater velocity profile.
+ easier to calibrate MAF (less variability)
- increased pressure drop (lower mass flow efficiency AKA VE)
+ easier to calibrate MAF (less variability)
- increased pressure drop (lower mass flow efficiency AKA VE)
03-18-2005, 03:08 PM
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Bowtieman is correct with what he said. I think he works on green or yellow things.lol If you remove the screen you will change the calibration of the MAF. DO NOT remove the screen unless u tune the table in the ECU. The screen is not keep bolts out of the motor. If U want to get the most power remove the screen and port the housing. NEXT port the throttle body. FIX the VE in the PCM with the MAF unplugged. Plug in MAF and calibrate the MAF table.
IF YOU ARE NOT TUNING DO NOTHING TO MAF it will change your air-fuel ratio.
IF YOU ARE NOT TUNING DO NOTHING TO MAF it will change your air-fuel ratio.
03-18-2005, 03:30 PM
#31
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Originally Posted by technical
But what does shape have to do with mass?
The sensor reads air velocity at a specific location. If the profile is linear "flat" then it doesnt matter where the sensor is located. Its the same velocity everywhere.
However if the the profile is parabolic, sensor location greatly affects what it reads. Air velocity is higher at the center and zero at the outside. Unless the MAF sensor is calibrated for a specific velocity profile, it may read the wrong net airflow. Remember that air velocity and air flowrate are two different things. One is how "fast" the air travels, the other is how much air goes through.
Old school term for mass flow efficiency is volumetric efficiency (VE). The MAF screen hinders air from filling the cylinder. From a scientific standpoint, VE is a function of bore x stroke and remains the same regardless. Its always 5.7 liters. However, air density and mass flow efficiency determine final HP.
03-18-2005, 03:55 PM
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The MAF doesn't measure velocity. Otherwise it would be a VAF. It measures the mass of air. Velocity is irrelavant to the mass of the air and ultimately the air fuel ratio. Temperature effects the mass as well. Velocity may stay the same at 40 degrees and 90 degrees but the mass is very different. I don't see how measuring velocity before the throttle would indicate anything for the ECM since the velocity will change once the air has entered the intake.
I still see no evidence pointing to the screen providing air flow manipulation.
I still see no evidence pointing to the screen providing air flow manipulation.
03-18-2005, 04:34 PM
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Originally Posted by technical
The MAF doesn't measure velocity. Otherwise it would be a VAF. It measures the mass of air. Velocity is irrelavant to the mass of the air and ultimately the air fuel ratio.
Velocity x cross section area x density = mass
Done
03-18-2005, 04:38 PM
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Originally Posted by YellowToy/A
Bowtieman is correct with what he said. I think he works on green or yellow things.lol If you remove the screen you will change the calibration of the MAF. DO NOT remove the screen unless u tune the table in the ECU. The screen is not keep bolts out of the motor. If U want to get the most power remove the screen and port the housing. NEXT port the throttle body. FIX the VE in the PCM with the MAF unplugged. Plug in MAF and calibrate the MAF table.
IF YOU ARE NOT TUNING DO NOTHING TO MAF it will change your air-fuel ratio.
IF YOU ARE NOT TUNING DO NOTHING TO MAF it will change your air-fuel ratio.
03-18-2005, 08:57 PM
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Technical I see at lest two people here that make a living working at engine OEMs telling you the same thing. If the air is not flowing smoothly thought the pipe it is hard to measure. The screen in the front and the screen back will change how the air flows in the pipe. The MAF does not measure velocity, but velocity of the air is the largest contributor to how much mass moves down the pipe. The flow is measured at few points with the MAF. If that flow is not constant across the pipe it will be hard to measure. Think of water moving a pipe. If the water is turning a corner it will be pushed to the side of the pipe. The screen will slow it down and the water will flow smoothly. That is why the second screen will help it will back up the flow like a dam. I have never seen two but it will work like that.
03-19-2005, 10:13 AM
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Originally Posted by YellowToy/A
Bowtieman is correct with what he said. I think he works on green or yellow things.lol If you remove the screen you will change the calibration of the MAF. DO NOT remove the screen unless u tune the table in the ECU. The screen is not keep bolts out of the motor. If U want to get the most power remove the screen and port the housing. NEXT port the throttle body. FIX the VE in the PCM with the MAF unplugged. Plug in MAF and calibrate the MAF table.
IF YOU ARE NOT TUNING DO NOTHING TO MAF it will change your air-fuel ratio.
IF YOU ARE NOT TUNING DO NOTHING TO MAF it will change your air-fuel ratio.
"SLP's high-performance 85mm mass-air-flow sensor flows a whopping 895 CFM (90 more than the stock 75mm MAF) enough to improve engine output by up to 10 horsepower. Or, remove the screen (not recommended on street cars) for an incredible 1000 CFM of air flow! This lightweight composite unit weighs one pound less than the factory MAF and is fully capable of supporting engine applications making over 600 horsepower. Compatible with stock and modified engines". They also say "For stock PCM's".
Last edited by cicerofire; 03-19-2005 at 10:24 AM.
03-19-2005, 10:27 AM
#37
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-If- the airflow is uniform across the face, or if it's
nonuniform in a way that happens not to matter,
then the screen is only a restriction.
If the intake tract biases the airflow then the sceen
fights that and stays closer to the "true" calibration
than without.
This is going to come down to cases, the lid in particular
on an Fbody is most of the intake tract and how it
shapes the airflow is going to matter to whether you
see a difference or not.
If you try it out in a nondestructive way you can always
go back if you don't like it. Aside from the sucking-up-
bolts thing, which is more a matter of hygeine.
nonuniform in a way that happens not to matter,
then the screen is only a restriction.
If the intake tract biases the airflow then the sceen
fights that and stays closer to the "true" calibration
than without.
This is going to come down to cases, the lid in particular
on an Fbody is most of the intake tract and how it
shapes the airflow is going to matter to whether you
see a difference or not.
If you try it out in a nondestructive way you can always
go back if you don't like it. Aside from the sucking-up-
bolts thing, which is more a matter of hygeine.
03-19-2005, 10:27 AM
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Cicero
The MAF is calibrated with the screen on . Did you monitor the trim in the PCM before and after the change? You need to do it on the same day because they will change day to day. The PCM will trim the change out(no screen) and you will never see it unless you look but the trims will change.
The MAF is calibrated with the screen on . Did you monitor the trim in the PCM before and after the change? You need to do it on the same day because they will change day to day. The PCM will trim the change out(no screen) and you will never see it unless you look but the trims will change.
03-19-2005, 11:51 AM
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Originally Posted by SSpeedracer
Einstein -
Velocity x cross section area x density = mass
Done
Velocity x cross section area x density = mass
Done
Originally Posted by YellowToy/A
Technical I see at lest two people here that make a living working at engine OEMs telling you the same thing. If the air is not flowing smoothly thought the pipe it is hard to measure. The screen in the front and the screen back will change how the air flows in the pipe. The MAF does not measure velocity, but velocity of the air is the largest contributor to how much mass moves down the pipe. The flow is measured at few points with the MAF. If that flow is not constant across the pipe it will be hard to measure. Think of water moving a pipe. If the water is turning a corner it will be pushed to the side of the pipe. The screen will slow it down and the water will flow smoothly. That is why the second screen will help it will back up the flow like a dam. I have never seen two but it will work like that.
For some reason I just can't picure this. I looked that the 30 second sketch, but can't understand how mass changes that way. Maybe I'm confusing mass with pressure?
I thought --> density * volume = mass?
03-19-2005, 12:19 PM
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technical
The sensor measures the mass of air that is going into the engine over time. This is in pounds per minute of air. What the PCM is trying to do is find out how much air is in cyl. If the MAF sensor is wrong the PCM will put in more or less fuel to get the air/fuel mix what it thinks it should be. The big part of what the senor measures is velocity of the air over time to get mass of air that goes into the engine over time. The mass of air has to be corrected for things like temp and density.
The sensor measures the mass of air that is going into the engine over time. This is in pounds per minute of air. What the PCM is trying to do is find out how much air is in cyl. If the MAF sensor is wrong the PCM will put in more or less fuel to get the air/fuel mix what it thinks it should be. The big part of what the senor measures is velocity of the air over time to get mass of air that goes into the engine over time. The mass of air has to be corrected for things like temp and density.