[Gmecm] Ideal gas law and $58

[Rob Handley]

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