[Diy_efi] Hotwire AFM at other than atmospheric pressures

Mike niche
Tue Sep 4 07:14:34 UTC 2007

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...


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

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

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