[Gmecm] Ideal gas law and $58

[not a webot]

compressor (it is a turbo cal right?) nonlinearities? It might also be cold
start enrichment related.
just the 2 first thoughts I had

On 9/24/07, Rob Handley <Robin at furyworld.fsnet.co.uk> wrote:
>
> Don't know whether anybody's interested :-) but I have now perfectly
> matched
> every factor in $58's steady state (meaning: no acceleration enrichment
> or deceleration enleanment or closed loop or any other special
> contributions)
> injector base pulse width calculation with its equivalent derived directly
> from the ideal gas law. It is now absolutely clear that the (F31M) inverse
> MAT/IAT
> look-up array has been 'adjusted' from theoretically correct, for whatever
> reasons.
>
> This plot: http://213.162.107.39/temp/GM_inverseIATfactor_vs_IAT.gif shows
> the only contribution that the MAT/IAT makes to the steady state BPW
> calculation. The contribution is made via a multiplying factor in the
> range
> 0 to 1.
>
> The magenta line is the multiplying factor arising from the values that GM
> put in the (F31M) inverse MAT/IAT look-up array for the Sunbird. The dark
> blue line
> is the theoretically correct multplying factor.
>
> The GM contribution stops changing at 23.5C but only matches the
> theoretical
> line at 50 C. So why would GM make it such that the mixture was lean below
> 50 C and rich above it? Is 50 C the normal running air temperature for the
> Sunbird?
>
> Rob
>
> ----- Original Message -----
> From: "Dig" <turbodig at yahoo.com>
> To: <gmecm at diy-efi.org>
> Sent: 17 September 2007 18:37
> Subject: Re: [Gmecm] Ideal gas law
>
>
> Yup.  In fact, if I remember the Sunbird cal correctly, they're exactly
> the
> same.
> Given that one application is intercooled, and the other isn't, you would
> have thought these would have been markedly different.
>
> ----- Original Message ----
> From: Rob Handley <Robin at FuryWorld.fsnet.co.uk>
> To: gmecm at diy-efi.org
> Sent: Monday, September 17, 2007 12:18:23 PM
> Subject: Re: [Gmecm] Ideal gas law
>
> I have no reason to think the lookup isn't working. The values in the
> standard Sunbird F31M array are fixed for MAT = 23.5 C and above. Is it
> the
> same for the Sy/Ty ?
>
> Rob
>
> ----- Original Message -----
> From: "Dig" <turbodig at yahoo.com>
> To: <gmecm at diy-efi.org>
> Sent: 17 September 2007 14:37
> Subject: Re: [Gmecm] Natural gas law
>
>
> Are you talking about the values in the table, or are you saying the
> lookup
> isn't working?
>
> The factory calibration was, "less than perfect".
>
> The other thing at work here, is the fact that when temps heated up, they
> wanted a bit extra fuel to keep the detonation demons away.  24 c is a bit
> low to start doing that, IMO.
>
> Later,
>
> Dig
>
>
> ----- Original Message ----
> From: Rob Handley <Robin at FuryWorld.fsnet.co.uk>
> To: gmecm at diy-efi.org
> Sent: Saturday, September 15, 2007 10:15:46 AM
> Subject: [Gmecm] Natural gas law
>
> I've been trying to match the $58 BPW calculation with a hand made BPW
> calculation spreadsheet - which is based on the natural gas law.
>
> What's confusing me ATM is that, in $58, the inverse air temperature
> correction factor (array F31M) does not change when the MAT value is >23.5
> C.
>
> Since gas mass is inversely proportional to gas temperature (if pressure
> and
> volume are constant), the MAT contribution should have an effect at all
> temperatures, and this effect IS significant above 23.5 C.
>
> What am I missing?
>
> Rob
>
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