MAF Flow tables?
09-15-2009, 08:56 PM
#1
MAF Flow tables?
I am looking to make a "flow bench", and I use that term lightly, out of a shop vac and an SLP MAF. I can power the maf off a motorcylce battery and put an ammeter to measure amp draw and it should work. I just need the amp draw and associated CFM for an SLP LS1 MAF. Anyone know where I can get something like that?
09-15-2009, 09:44 PM
#2
Different vehicles/pcms have different calculation bases or curves. The maf is not a correct data giver, just a 5volt source with a thin wire on one end that is heated up and the pcm makes a calculation at how much current it takes to keep the thin wire at a set "state". I am not sure amps would work well. But I could be wrong, I guess milliamps could be read, it is a load and therefore has a draw. But I bet it wouldn't be too precise. Hertz is what the pcm will reference and "associate" with a particular airflow. Even then they make it freaking confusing by never really referencing cfm or something normal people can relate to. It's gotta be grams or lbs.
LIke the lingenfelter 100mm maf. It has multiple curves for different vehicles.
http://www.lingenfelter.com/sites/li...05-2006MAF.pdf
LIke the lingenfelter 100mm maf. It has multiple curves for different vehicles.
http://www.lingenfelter.com/sites/li...05-2006MAF.pdf
09-15-2009, 09:56 PM
#3
That all makes sence, but from the understanding that I have of MAFs, explained to me by a tuner in seattle (I forgot his name, well known in the LT1 arena, Vince maybe) is that among other things, the PCM measures amp draw at the MAF to calculate incoming air volume. This is also combined with temp and pressure for accuracey. This method is effectively the same as a "hot wire anemometer", except that I would have to correct for temp and pressure if I use a MAF. Does this sound reasonable?
09-16-2009, 07:47 AM
#5
Dewmanshu, I am still a bit basic in my understanding of current flow (draw). Can you explain the relationship between amp draw and Htz? If I can understand that relationship, I might be able to come up with a cheap, accurate flow meter.
09-16-2009, 08:35 AM
#6
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well, current flow measures exactly how much electricity is flowing through a system. hertz is a measure of frequency, like in a computer, processor speed is measured in hertz - how many operations can be performed in one second. in the case of my laptop, is is 2660 operations per second or 2660 Hz or 2.66GHz. you could also think about cordless phones 2.4 GHz means that signals are sent and received 2400 times per second.
hope this helps
hope this helps
09-16-2009, 08:47 AM
#7
well, current flow measures exactly how much electricity is flowing through a system. hertz is a measure of frequency, like in a computer, processor speed is measured in hertz - how many operations can be performed in one second. in the case of my laptop, is is 2660 operations per second or 2660 Hz or 2.66GHz. you could also think about cordless phones 2.4 GHz means that signals are sent and received 2400 times per second.
hope this helps
hope this helps
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09-16-2009, 09:02 AM
#8
I got this from http://www.engine-light-help.com/mas...ow-sensor.html
With that said, and GM MAFs being hot "wire" not hot "film", it seems that I should be able to associate voltage to a given volume of air, right? Or is there still something that I am not understanding? 
The main purpose of the Mass Air Flow (MAF) Sensor is to measure the volume and density of air entering the engine at any given time. The computer uses this information in conjunction with input from other sensors, to calculate the correct amount of fuel to deliver to the engine. Input from this sensor is also used indirectly to help calculate desired ignition timing and transmission operating strategies. MAF sensors are mainly designed as a "hot wire" sensor or a "hot film" sensor. Both sensors function in a similiar fashion. Hot wire sensors pass current across a platinum wire and hot film sensors pass current across a foil grid. The current level is regulated to maintain the hot wire, or film, at a predetermined temperature. This temp is either a direct value, or a value that is a set number of degrees above ambient (outside) air temperature.
So how does this tell us how much air is getting into the engine? Well, as air passes across the mass air flow sensor, it cools the hot wire, increasing the amount of current needed to keep that wire at the specified temperature. The amount that the wire is cooled is directly proportional to the temperature, density and humidity of the air passing through the sensor and as such, the current increase needed to heat the wire allows the computer to easily calculate the volume of air entering the engine.
mass air flow sensor
Mass air flow sensors typically either send a voltage, or frequency signal to the powertrain control module (PCM). Hot wire sensors typically have an operating range of 0 - 5 volts, with idle voltage being around .5 - .8 volts and full throttle application is normally between 4 and 5 volts. Hot film sensors typically produce a frequency out put of 30 - 50 Hz with 30 Hz being idle and 150 Hz at full throttle. There are some other subtle differences between the sensors but these do not affect function or purpose.
So how does this tell us how much air is getting into the engine? Well, as air passes across the mass air flow sensor, it cools the hot wire, increasing the amount of current needed to keep that wire at the specified temperature. The amount that the wire is cooled is directly proportional to the temperature, density and humidity of the air passing through the sensor and as such, the current increase needed to heat the wire allows the computer to easily calculate the volume of air entering the engine.
mass air flow sensor
Mass air flow sensors typically either send a voltage, or frequency signal to the powertrain control module (PCM). Hot wire sensors typically have an operating range of 0 - 5 volts, with idle voltage being around .5 - .8 volts and full throttle application is normally between 4 and 5 volts. Hot film sensors typically produce a frequency out put of 30 - 50 Hz with 30 Hz being idle and 150 Hz at full throttle. There are some other subtle differences between the sensors but these do not affect function or purpose.
09-16-2009, 09:26 AM
#9
Hmmm...I may have been a little too crude in my explanation of the "hot" wire. I believe the newer style GM MAFs use a sensor that is needed for all of the inductive readings. The pcm will be seeing the frequencies not draw (there isn't too much relationship for our discussion like explained above). Quite complicated I guess...get your hands on a "hot wire" style maf instead of the probable "cold wire" style you have and you can accomplish what you want. The one you have will work if you get an oscilloscope.
09-16-2009, 09:32 AM
#10
The voltage question you just asked... I have a feeling you are never going to be able to come up with (find) a premade table or graph for set values on cfm vs voltage or amps. The best is going to be frequency vs some air flow measurement.
If you do, it will be for the older "hot wire" set ups and therefore you are going to need to get your hands on a real "hot wire" MAF that is meant to be read with amps/load.
If you do, it will be for the older "hot wire" set ups and therefore you are going to need to get your hands on a real "hot wire" MAF that is meant to be read with amps/load.