Air flow meter to MAP conversion

[amichie]

Anybody know the relationship between airflow and manifold pressure in an NA engine.

I assume the closer to atmospheric pressure in the manifold the greater is the airflow.

What abour RPM?

A wide open throttle at low rpm under load would produce near atmospheric pressure in the manifold but perhaps not high airflow.

[wilbo666]

You've got a bit of electrical prowess,

Why not make a device that has

Inputs:
>Airflow (existing AFM)
>MAP (hook up the MAP sensor you want to use!)
>RPM
>TPS (I don't think this will really tell you much, but might as well log?)

From that you should be able to construct a lookup table of sorts (or work out the equation ) to allow you to convert the MAP voltage to the expected AFM voltage!

You're 100% that any box of tricks will need RPM, as you said, WOT at idle isn't as much airflow as WOT @ 6000rpm (but MAP should be similar ).


Edit:
In fact I might be able to lend you a box of tricks to do the logging if you want / need?

Cheers
Wilbo

[manny]

And if it gets too hard you can just try a MAP ECU

[amichie]

You've got a bit of electrical prowess,

Why not make a device that has

Inputs:
>Airflow (existing AFM)
>MAP (hook up the MAP sensor you want to use!)
>RPM
>TPS (I don't think this will really tell you much, but might as well log?)

From that you should be able to construct a lookup table of sorts (or work out the equation ) to allow you to convert the MAP voltage to the expected AFM voltage!

You're 100% that any box of tricks will need RPM, as you said, WOT at idle isn't as much airflow as WOT @ 6000rpm (but MAP should be similar ).


Edit:
In fact I might be able to lend you a box of tricks to do the logging if you want / need?

Cheers
Wilbo

I've been building a box today that will give me an airflow meter and a MAP sensor output.

The MAP I have is from a ford and converts the pressure into a square wave with the frequency varying from about 80 to 160 Hz.

I also have a hot wire MAF from a holden that also gives a frequency output.

I will bodge the whole thing together with duct tape and compare the outputs.

I might take you up on that offer of the data logger. I'll get back to you when I decide which way to go.

[brett_celicacoupe]

you might need intake air temp as im pretty sure a AFM would measure air mass flowing through it.

jaycar have those 128 load point 5v signal adjusters too

[brett_celicacoupe]

http://www.geocities.com/MotorCity/P...ject/AFMs.html

small amount of relevant info there

[amichie]

http://www.geocities.com/MotorCity/P...ject/AFMs.html

small amount of relevant info there

Thanks for that link. The toyota traindocs just show voltage output versus flap opening angle. Voltage versus airflow is more useful.

I also forgot about the JAYCAR adjuster. It might be the cheapest solution of all.

DO you know if the JAYCAR unit will accept a frequency input??

[wilbo666]

Can I ask why you are using a MAP sensor that outputs a frequency as opposed to the generic type that outputs an approx 0-5V signal?



Cheers
Wilbo

[JustCallMeOrlando]

Seconded. Just get a normal one, the voltage will be much easier to play with than a frequency.

[amichie]

Can I ask why you are using a MAP sensor that outputs a frequency as opposed to the generic type that outputs an approx 0-5V signal?



Cheers
Wilbo

I just happened to have a ford one. I didn't realise that other MAP sensor were more simple.

Can I ask what models use a 0-5V unit? Are the cheapies on ebay the generic type?

[Duk]

I also forgot about the JAYCAR adjuster. It might be the cheapest solution of all.

DO you know if the JAYCAR unit will accept a frequency input??

It doesn't.

[wilbo666]

I just happened to have a ford one. I didn't realise that other MAP sensor were more simple.

Can I ask what models use a 0-5V unit? Are the cheapies on ebay the generic type?

Almost anything else!

I've got a GM one and plug I'll send you for the cost of postage if ya want?

Cheers
Wilbo

[amichie]

Almost anything else!

I've got a GM one and plug I'll send you for the cost of postage if ya want?

Cheers
Wilbo

Yes please. PM me some details and I will direct deposit. Since my car is NA I think virtually anything will work. I would love to try and move it around the intake to try and figure out where any restrictions might be. I have long suspected MY LPG carb as a major restriction. I'd love to know the pressure drop across it.

[Duk]

I have long suspected MY LPG carb as a major restriction. I'd love to know the pressure drop across it.

http://www.autospeed.com/cms/A_110210/article.html

[oldcorollas]

these kind of MAP sensors (MPX4250 etc) are cheap... well.. about $15-20 from digikey. same as used in Megasquirts
http://www.freescale.com/files/senso...t/MPX4250A.pdf

[amichie]

these kind of MAP sensors (MPX4250 etc) are cheap... well.. about $15-20 from digikey. same as used in Megasquirts
http://www.freescale.com/files/senso...t/MPX4250A.pdf

That is just what I'm looking for. I might build a board with a few of these and plumb it into my intake at a number of points.

[oldcorollas]

there are also two port differential versions as well

[Duk]

there are also two port differential versions as well

Probably the prefered type, to compensate for changes in atmospheric pressure/altitude.

[brett_celicacoupe]

you can always use a U-tube manometer to look for pressure differences.

not hard to make either (clear hose + water)

[amichie]

you can always use a U-tube manometer to look for pressure differences.

not hard to make either (clear hose + water)

Agreed. Worth a try.