I am going to elaborate on this basis for an addition here. I typed it up during a lab section I had to be in, but was already done with. Maybe we can get a good "FAQ you" type thing going or something?
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Most MAF's display their airflow as simple voltage curve. The voltage starts out low and gets higher as airflow increases. This voltage change is not at a linear rate to the change in airflow.
Most MAF's have voltage output that can reach 6.5volts DC or even higher with enough airflow. The AFM also needs a reasonable minimum voltage to meter air at idle. Our ECU can read a maximum of 5.12volts DC, which depending on the airflow metering device used could be moving 300CFM or 1000+CFM of air.
The translation a stock ECU (or any ECU/PCM really) uses is referred to as a Transfer Function or a VQ Map. This is simply a lookup table that the ECU uses to determine how much air is being pulled through the MAF based on the voltage it receives from the MAF. There are additional tables on top of this for things like cold start, etc. The K value is stacked on to adjust for injector size, the dwell (void) time is also added to account for the time it takes the injectors to open. All of this is used to determine injector pulse-width (how much fuel is injected). This is a well-coordinated system capable of doing hundreds of calculation in a second. The system works so fast, it can almost act as if the engine were sitting still.
Finding a MAF capable of metering the amount of air your engine is capable of moving can be hard. There are many options available to both upgrade the MAF (or upgrade away from MAF entirely), and extend the metering of a MAF you have, or both.
An engine does not 'care' what kind of engine management system it is running. If required timing and fuel requirements are met and all other variables are exactly equal, the engine will perform almost exactly the same from system to system. The only difference is going to be inlet restriction based on the maf used, and depending on where it is located. Generally speaking, MAF is superior to Speed-Density (SD) when performance modifications are considered on factory cars. To put it simply SD has a "preconceived notion" of how much air the engine is getting based on its factory volumetric efficiency. Do anything to change that (exhaust, cams, etc) and you can throw your whole system off and lose power, or not gain any power at all. From an aftermarket standpoint, speed-density can be tailored specifically to the modified engine the system is being run on and does not have the drawback of having to have a sometimes bulky sensor in the airstream. For any typical aftermarket system to even match the performance across the board compared to a factory system takes hours and hours of time to develop a tune that works in all conditions (something the factory did for you already, but obviously they designed it for a stock engine).
A MAF, MAS, and AFM are not always the same thing. A MAF (Mass Air Flow) meter is the same thing as a MAS (Mass Air Sensor) but not the same thing as an AFM (Air Flow Meter). Though these terms are used interchangeably you should know they are in fact not the same.
Methods for getting the most out of your air metering:
1. Voltage Drop - commonly used to obtain a lower MAF voltage read by the ECU. The voltage of the MAF must extend beyond the measuring range of the ECU (most do) for this to work. You can use a Potentiometer to adjust the voltage (with one terminal going to ground, one to the maf and one to the ECU to "ground out" some of the signal voltage), and a modified VQmap or modified fuel map to account for the difference.
2. Air Bypass - Simple and probably the most effective means. Ashz's DoolZ and the JWT dual-pop both work on the same principal. Not all air is metered, but the difference is accounted for in the VQmap or fuel map. It can be a pain to tune correctly, but once established it is a good method to both releve the restriction of a maf, and the limitations of its metering ability.
3. Larger MAF sample tube – Cut apart the MAF and put it in a bigger housing. This reduces the airflow past the sensor itself by the amount equal to the increase in cross-sectional area of the tube.
3. Upgraded MAF From another car- Easy to do if you have either a VQmap for the new MAF, or a way to make one.
4. Custom made MAF - A few shops exist that custom make MAF's for a given application. Fine adjustments to a MAF may allow it to work as a blow-through (where the maf could be located by the throttle body in a pressurized system), be less restrictive, and offer greater metering ability. The recently defunct PRO-M was one of the most popular shops for making this type of custom MAF.
5. AFC or similar device - Plug and play voltage trimming, very user-friendly, but more or less a band-aid fix for making a new VQmap.
6. MAF Translator - Allows use of a GM MAF, which outputs a square-wave frequency instead of a voltage signal. The translator can be set to scale the frequency and output many different voltage curves for your ECU to read. Hence it "translates the airflow" from the seemingly limitless GM sensors into a format your ECU can read.
7. MAP ECU or similar - Uses a Manifold Absolute Pressure (MAP) sensor, engine RPM and air temperature to figure the amount of air the engine is moving, effectively converting your MAF system to speed-density. The MAP ECU feeds your ECU the correct voltage based on internal functions that you can program.
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Most MAF's display their airflow as simple voltage curve. The voltage starts out low and gets higher as airflow increases. This voltage change is not at a linear rate to the change in airflow.
Most MAF's have voltage output that can reach 6.5volts DC or even higher with enough airflow. The AFM also needs a reasonable minimum voltage to meter air at idle. Our ECU can read a maximum of 5.12volts DC, which depending on the airflow metering device used could be moving 300CFM or 1000+CFM of air.
The translation a stock ECU (or any ECU/PCM really) uses is referred to as a Transfer Function or a VQ Map. This is simply a lookup table that the ECU uses to determine how much air is being pulled through the MAF based on the voltage it receives from the MAF. There are additional tables on top of this for things like cold start, etc. The K value is stacked on to adjust for injector size, the dwell (void) time is also added to account for the time it takes the injectors to open. All of this is used to determine injector pulse-width (how much fuel is injected). This is a well-coordinated system capable of doing hundreds of calculation in a second. The system works so fast, it can almost act as if the engine were sitting still.
Finding a MAF capable of metering the amount of air your engine is capable of moving can be hard. There are many options available to both upgrade the MAF (or upgrade away from MAF entirely), and extend the metering of a MAF you have, or both.
An engine does not 'care' what kind of engine management system it is running. If required timing and fuel requirements are met and all other variables are exactly equal, the engine will perform almost exactly the same from system to system. The only difference is going to be inlet restriction based on the maf used, and depending on where it is located. Generally speaking, MAF is superior to Speed-Density (SD) when performance modifications are considered on factory cars. To put it simply SD has a "preconceived notion" of how much air the engine is getting based on its factory volumetric efficiency. Do anything to change that (exhaust, cams, etc) and you can throw your whole system off and lose power, or not gain any power at all. From an aftermarket standpoint, speed-density can be tailored specifically to the modified engine the system is being run on and does not have the drawback of having to have a sometimes bulky sensor in the airstream. For any typical aftermarket system to even match the performance across the board compared to a factory system takes hours and hours of time to develop a tune that works in all conditions (something the factory did for you already, but obviously they designed it for a stock engine).
A MAF, MAS, and AFM are not always the same thing. A MAF (Mass Air Flow) meter is the same thing as a MAS (Mass Air Sensor) but not the same thing as an AFM (Air Flow Meter). Though these terms are used interchangeably you should know they are in fact not the same.
Methods for getting the most out of your air metering:
1. Voltage Drop - commonly used to obtain a lower MAF voltage read by the ECU. The voltage of the MAF must extend beyond the measuring range of the ECU (most do) for this to work. You can use a Potentiometer to adjust the voltage (with one terminal going to ground, one to the maf and one to the ECU to "ground out" some of the signal voltage), and a modified VQmap or modified fuel map to account for the difference.
2. Air Bypass - Simple and probably the most effective means. Ashz's DoolZ and the JWT dual-pop both work on the same principal. Not all air is metered, but the difference is accounted for in the VQmap or fuel map. It can be a pain to tune correctly, but once established it is a good method to both releve the restriction of a maf, and the limitations of its metering ability.
3. Larger MAF sample tube – Cut apart the MAF and put it in a bigger housing. This reduces the airflow past the sensor itself by the amount equal to the increase in cross-sectional area of the tube.
3. Upgraded MAF From another car- Easy to do if you have either a VQmap for the new MAF, or a way to make one.
4. Custom made MAF - A few shops exist that custom make MAF's for a given application. Fine adjustments to a MAF may allow it to work as a blow-through (where the maf could be located by the throttle body in a pressurized system), be less restrictive, and offer greater metering ability. The recently defunct PRO-M was one of the most popular shops for making this type of custom MAF.
5. AFC or similar device - Plug and play voltage trimming, very user-friendly, but more or less a band-aid fix for making a new VQmap.
6. MAF Translator - Allows use of a GM MAF, which outputs a square-wave frequency instead of a voltage signal. The translator can be set to scale the frequency and output many different voltage curves for your ECU to read. Hence it "translates the airflow" from the seemingly limitless GM sensors into a format your ECU can read.
7. MAP ECU or similar - Uses a Manifold Absolute Pressure (MAP) sensor, engine RPM and air temperature to figure the amount of air the engine is moving, effectively converting your MAF system to speed-density. The MAP ECU feeds your ECU the correct voltage based on internal functions that you can program.
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