[Diy_efi] Hotwire AFM at other than atmospheric pressures

[David Allen]

  Just a small observation - the datasheet does say it measures 
independantly of air density.  That would make me beleive it would still 
register accurate mass-flow even under pressure.
  You might look at the sealing of the electronics package on top of the 
meter - from my euro car days I remember these open to the inside of the 
meter housing where the measured airflow is.  The circuitry was covered in 
soft gel.  If the measured air were way above atmospheric, it could force 
pressure inside the housing with the meter's electronics, then allow the gel 
to be expelled into the air stream as the pressure was released.  Just my 
two cents worth!
David


----- Original Message ----- 
From: "Mike" <niche at iinet.net.au>
To: <diy_efi at diy-efi.org>
Sent: Tuesday, September 04, 2007 2:14 AM
Subject: [Diy_efi] Hotwire AFM at other than atmospheric pressures


> Hi Chaps,
>
> Many years ago I recall reading in respect of the traditional hot wire 
> AFM's
> that Bosch suggested they not be used much above atmospheric pressure
> and were generally designed for use at intakes to engines that used turbos
> and not in any way on the compressor outlet regardless of charge 
> temperature.
>
> There are a few people however using them reliably on the exit of 
> intercoolers
> up to approx 10-20psi boost on ECU's that have no method of pressure 
> sensing,
> such as the factory Bosch/Hitachi ECU used on RB30 motors etc... Its also
> been observed that for large Intercoolers its beneficial to run them 
> afterwards
> if at least for faster transient load response.
>
> Here is a data sheet for the VLT Commodore AFM but I cant see any 
> exception
> report re operation at pressure, given the hot wire AFM is for the most 
> part a
> true mass flow sensing device then can anyone guess the issue re operation
> at 20psi - other than perhaps a structural failure and/or can someone 
> hazard
> a guess what the type of derating might be operating at that higher 
> pressure,
> such as running leaner in that it would report less flow than actually 
> exists etc...
>
> http://niche.iinet.net.au/VL_Technical/Bosch_MAF_900Kg.pdf
>
> Observations welcome ?
>
> Incidentally, the part number on the VLT Holden Commodore unit is 0 280 
> 212 008
> and I'm advised its the 900Kg range (but now I cant be sure) however, it 
> doesnt match
> the part number in the PDF file I got from a techie working for GMH many 
> years ago :-(
>
> Anyone have a PDF of the 0 280 212 008  AFM by chance ?
>
>
>
>
>
> Regards from
>
>
> Mike
> Perth, Western Australia
> VK/VL Commodore Fuse Rail panel that wont warp, twist or melt, guaranteed 
> !
> Twin tyres for most sedans, trikes and motorcycle sidecars
> http://niche.iinet.net.au
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