Air Flow Meter discussion (WAS: "I'm missing something...)

[Will Reeve]

http://www.carlton24v.co.uk/efilist/afmvmap.csv comma separated text file.
It's just a section of the large amount of data I collected. In the end we
decided to go the MAF route as to use the MAP output we needed rpm as well
to simulate AFM signal correctly. Also the engine seemed to go "atmospheric"
full scale quite quickly, the AFM still had quite a bit of dynamic range
left before it full scaled.

Will
P.S. MAF (hot film) has been bought but not installed yet, other things
cropped up a slowed us down!

-----Original Message-----
From: owner-diy_efi at diy-efi.org [mailto:owner-diy_efi at diy-efi.org]On
Behalf Of Bruce
Sent: 18 November 2000 20:55
To: diy_efi at diy-efi.org
Subject: Re: Air Flow Meter discussion (WAS: "I'm missing something...)



You wouldn't happen to have it in a different formate would you?.
Bruce

From: "Will Reeve" <will at reeve.org.uk>
Subject: RE: Air Flow Meter discussion (WAS: "I'm missing something...)
> have a look at
> http://www.carlton24v.co.uk/efilist/afmvmap.zip
> Microsoft excel spreadsheet containg part of a data log between the AFM (a
> bosch flap device) and a map sensor on my car. Both signals were
'straight'
> from the sensor. I was investigating it for the inlet tract restriction
> reduction. You can see the pressure waveform on the MAP trace if you zoom
> in!
> Will

> Behalf Of Bruce
> Sent: 17 November 2002 00:25
> To: diy_efi at diy-efi.org
> Subject: Re: Air Flow Meter discussion (WAS: "I'm missing something...)
> Yep, I used to think that too.
> Until someone challenged me with his results.
> Then I data logged both my MAF and installed a MAP.
> It looks to be a tie or the MAF is slightly faster.
> The MAF was a processed output and the MAP was raw data.
> The thermistor in the new GM MAFs is very small.
> Bruce

> From: "Kevin _" <kiggly at hotmail.com>
> > Unfortunately, in the automotive world, all the aforementioned sensors
> > besides the MAP are VERY slow.  From the airflow change to its reported
> > measurement, you have a bare minimum of something like 20ms before all
the
> > corrections are applied.  On the hotwire, the automotive environment
> > requires a very durable sensor, so a big-ole thermistor is usually used
as
> > the hotwire element, which only adds to its latency.  Combine that with
> the
> > air response time of a turbo system that has 2 cubic feet of plumbing
that
> > is being compressed from 1:1 to 3:1 and you're in for some very
> > non-representative readings during spoolup and after you get off the
gas.
> > On the other hand, a general MAP sensor reacts in about 1ms.  This is by
> far
> > the superior way to go for making a drivable EFI setup.  With the
airflow
> > measuring devices, you'd probably have to wait about 4 engine cycles to
be
> > able to calculate an accurate airflow input at 9k rpm (13ms/cycle, total
> > wild guess of 40ms latency), where with the MAP setup you're able to
catch
> > it 1 cycle after the transition.  To take care of the latency issue, you
> > just have to piss fuel in with throttle transition corrections.
> > BTW - I just joined the list earlier today, there seems to be a lot of
> good
> > stuff here!
> > Kevin


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