Square wave signal from MAF sensor.

[Intuitivus]

Hi all,
Just found this forum by chance and maybe someone here can be helpful.
I'm looking to build a low cost flow bench for testing cylinder head airflow.Nothing fancy just something that can show differences before and after porting. Was thinking about using a MAF from a car as the sensor.I know there is a certain type that emits a square wave that changes with changes in air flow.I believe GM utilized this type at one time or another. I already have electronics to convert to CFM.

Does anyone know of a specific unit found on European vehicles that would meet my needs? And a data sheet,schematic,with conversion tables wouldn't be a bad idea either.

 

[JayMaechtlen]

I'm in the US, and can't offer specifics, but - you'd want a sensor that would measure a bit more than you expect your port to flow after the best possible porting job, right?
So figure that out, that would give you an idea of what size motor you'd want a sensor from.
Then look for MAFs with the appropriate signal format.
I think any number of GMs used that type of sensor - over here.
Don't know about Europe.
Check out the tuner forums for info.
Good Luck
Jay



Jay Maechtlen

http://www.laserpubs.com/techcomm

 

[decipha]

your are referring to a frequency based sensor, GM as well as a few others use them

A single cylinder head port will not flow anywhere near what most factory sensors are capable of measuring, however, the more measuring ability the sensor has the less resolution they typically have at very low flows, thus I recommend getting a sensor thats capable of ONLY measuring 120% of your expected peak airflow for greater resolution down low

The 'meter' includes the pipe inside diameter as well since they are dependent upon each other for airmass calibration

the center mounted MAF sensors tend to be less prone to turbulence and read a tad more stable as compare to offset sampling MAFs

 

[Intuitivus]

A single cylinder head port will not flow anywhere near what most factory sensors are capable of measuring, however, the more measuring ability the sensor has the less resolution they typically have at very low flows, thus I recommend getting a sensor thats capable of ONLY measuring 120% of your expected peak airflow for greater resolution down low

That's exactly what I was thinking, but what is low flow.I would think a MAF from a 2 liter 4 cylinder engine at idle speeds would be measuring low flow,but how low.I'm messing around with street heads,and 300 cfm is about the limit to what I want to be able to measure at high lift.At low lift say .200,I may not have the resolution to measure in the 90 to 150 cfm range with a MAF calibrated for 600cfm or more.
The pump I'm looking at is capable of 1210m³/hour (712cfm),so this is also maybe a little much.

I need to find some kind of documentation as to which MAF's are frequency based,and what cfm ranges they're rated for.

Or if anyone has a schematic as to exactly how something like this works,I could design my own for the ranges I need.

 

[GregLocock]

I'd have thunk the max flow rate for a MAF would be strongly related to redline rpm/60/2*capacity in m^3*1.22

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[decipha]

low flow is in reference to the sensors measuring ability, typically low air flow conditions that cause measuring instability occurs up to approximately 1.5% of the meters maximum measuring ability

this doesn't sound like much but when your dealing with an engine that requires a meter capable of measuring in excess of 1900 cfm (which is actually quite common on turbocharged v8 engines) that only idles at 1% to 1.1% of the meters capability (for example: 20 cfm, again typical modified v8) , it can cause some idle instability

most manufacturers leave about 25% headroom in the MAF

there are a few little tricks you can do to stabilize airflow for better measurements

honestly, you'd be better off using a voltage based MAF, some of the frequency based MAF's have an IC on them that converts voltage to hertz thus using voltage would eliminate that step and take up less processing power and time from an IC standpoint

its quite simple to do, about as easy as I just explained in this post, nothing fancy by any means

remember the "METERS" actual measuring ability is the culmination of the sensor element and its pipe diameter, you can simply put the meter in a larger pipe for increased measuring ability