MAT Correction
05-31-2012, 10:10 PM
#63
Thought I'd share what the values do so that you can see for youself how the code impacts fueling based on tempature and the various % in correction scaling.
The fueling is scaled by the % calculated in the last two columns (one is for 100% MAT scaling, the other is values used at 50% MAT scaling).
I'll admit I was quick to think a bug exists, but I still do feel the calculations are probably not ideal... note how the band of no correction (shown around 68-70F where it is at 100% correction) is only a small area whereby changing from 100% to 50% MAT scaling doesn't impact when a change is seen based on the rounding and resolution used in the maths in the code.
Interesting and I'll continue this in the MSExtra forum to see if I can get James or Ken to respond and reply.
The fueling is scaled by the % calculated in the last two columns (one is for 100% MAT scaling, the other is values used at 50% MAT scaling).
I'll admit I was quick to think a bug exists, but I still do feel the calculations are probably not ideal... note how the band of no correction (shown around 68-70F where it is at 100% correction) is only a small area whereby changing from 100% to 50% MAT scaling doesn't impact when a change is seen based on the rounding and resolution used in the maths in the code.
Interesting and I'll continue this in the MSExtra forum to see if I can get James or Ken to respond and reply.
Code:
F C 100% 50% Corr Corr 32 0 108 104 36 2 107 103 40 4 106 103 44 7 105 103 48 9 104 102 52 11 104 102 56 13 103 101 60 16 102 101 64 18 101 101 68 20 100 100 72 22 100 100 76 24 99 99 80 27 98 99 84 29 97 99 88 31 97 98 92 33 96 98 96 36 95 98 100 38 95 97 104 40 94 97 108 42 93 97 112 44 93 96 116 47 92 96 120 49 91 96
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06-01-2012, 07:56 AM
#67
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The fact that at 116F it is pulling 8% of fuel sounds great unless you are in boost on the track on a hot day in Miami and your AFR that should be ~12 and you are seeing a very dangerous 13.5.
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06-01-2012, 09:10 AM
#69
Based on the that table let's saying the code is using 21C/70F as it's 100%...ok cool. To calculate percent difference from that assumed "standard value".... I'm going to use Rankine cuz i'm in 'merica....
New temp 120F
(delta T) / (Abs temp original) = ((70 - 120) / (70+460))*100+100 = 90.56, rounded up to 91
Now I'll admit I've messed around with 68-72 as the 'starting value', and none of them match up exactly with the table you posted up....every now and then one value will be mismatched by 1, might be due to how MS if it's rounding the numbers intermediately along the way or something, I'm not sure.
As far as the validity of this.. i may be off in my thinking, but I was using the P=rho*R*T equation.... P and R are constant for our purposes, which leaves rho (density) and T(absolute) to be inversely proportional... ie temp increases by 2 percent, 2 percent less air mass for a given pressure...needs 2 percent less fuel. BUT we're probably getting into the weeds here into theoretical stuff, that probably does not apply exactly for us. If any of my thinking or logic is off, let me know what you think, definitely open to discussion and learning.
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06-01-2012, 09:20 AM
#70
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this is the formula:
n = PV/RT
=> M = n x MM = PV/RT x MM
= (VE * MAP * CYL_DISP) / (R * (IAT-32) * 5/9 + 273)) x MMair
P = VE * MAP (i.e. the pressure in the cylinder in kPa),
V = CYL_DISP = the displacement of one cylinder (in liters),
R = 8.3143510 J/mol K,
and T = (IAT-32)* 5/9 + 273 to convert IAT from °Fahrenheit to Kelvin.
Then to calculate fueling:
Req_Fuel is calculated from the equation:
REQ_FUEL*10 = 36,000,000 * CID * AIRDEN(100kPA, 70°F)/(NCYL*AFR*INJFLOW ) * 1/DIVIDE_PULSE
Where:
36,000,000 is the number of tenths of a millisecond in an hour, used to get the pounds per 1/10 milllisecond from the pounds/hours rating of the injectors.
REQ_FUEL = Computed injector open time in tenths of millisecond.
CID = Cubic Inch Displacement.
AIRDEN = Air density (pounds per cubic inch) at MAP pressure of 100 Kpa, Air Temperature of 70 Degrees F, and Barometric Pressure of 30.00 In HG
NCYL = Number of Cylinders
INJFLOW = Injector Flow Rate in pounds per hour.
DIVIDE_PULSE = injection divide number for number of injections per engine cycle.
The AIRDEN function (used above) is defined by:
AIRDEN(MAP, temp) = 0.0391568* (MAP*10-31.0)/((temp+459.7) * 1728)
Or, in metric units (kg/m3, °C, kPa):
AIRDEN(MAP, temp) = 1.2929 * 273.13/(T+273.13) * MAP/101.325
n = PV/RT
=> M = n x MM = PV/RT x MM
= (VE * MAP * CYL_DISP) / (R * (IAT-32) * 5/9 + 273)) x MMair
P = VE * MAP (i.e. the pressure in the cylinder in kPa),
V = CYL_DISP = the displacement of one cylinder (in liters),
R = 8.3143510 J/mol K,
and T = (IAT-32)* 5/9 + 273 to convert IAT from °Fahrenheit to Kelvin.
Then to calculate fueling:
Req_Fuel is calculated from the equation:
REQ_FUEL*10 = 36,000,000 * CID * AIRDEN(100kPA, 70°F)/(NCYL*AFR*INJFLOW ) * 1/DIVIDE_PULSE
Where:
36,000,000 is the number of tenths of a millisecond in an hour, used to get the pounds per 1/10 milllisecond from the pounds/hours rating of the injectors.
REQ_FUEL = Computed injector open time in tenths of millisecond.
CID = Cubic Inch Displacement.
AIRDEN = Air density (pounds per cubic inch) at MAP pressure of 100 Kpa, Air Temperature of 70 Degrees F, and Barometric Pressure of 30.00 In HG
NCYL = Number of Cylinders
INJFLOW = Injector Flow Rate in pounds per hour.
DIVIDE_PULSE = injection divide number for number of injections per engine cycle.
The AIRDEN function (used above) is defined by:
AIRDEN(MAP, temp) = 0.0391568* (MAP*10-31.0)/((temp+459.7) * 1728)
Or, in metric units (kg/m3, °C, kPa):
AIRDEN(MAP, temp) = 1.2929 * 273.13/(T+273.13) * MAP/101.325
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06-01-2012, 09:32 AM
#71
Would it be hard/possible to change Gair resolution to 0.1%? I don't think that's gonna solve anything like guys have talked about in here, but seems like a good idea overall for more accuracy. I've really liked the other recent changes in finer resolution... EGO, etc.
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06-01-2012, 09:39 AM
#72
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I dunno I dont really have a problem with the resolution of the table. I'm able to completely negate the density correction... It was as simple as putting the MS on a stim, turning the AIT input pot, and watching how the Gair reacted. I tuned it out completely within 0.5% (in some spots Gair stays at 100.5%--not going to make or break me).
When I always brought up the issue, it's been assumed that my AIT is reporting false temps, therefore that's scewing up the code. and to use the Mat corrections table in the fashion I do is only solving the flawed data from my sensor.
but i have proven that my sensor reports back readings that are very close to readings under the hood as seen by a second identical AIT sensor.
So while the gas density law is law. what the fueling code doesn't take into effect is how the temperature of say the block of even the fuel relate to the air density.
As far as driving, if I need different fueling requirements base on temp, my EGO takes care of it and in boost my AFRs are very consistent and flat regardless of the ambient temp...so I dunno what to say.
When I always brought up the issue, it's been assumed that my AIT is reporting false temps, therefore that's scewing up the code. and to use the Mat corrections table in the fashion I do is only solving the flawed data from my sensor.
but i have proven that my sensor reports back readings that are very close to readings under the hood as seen by a second identical AIT sensor.
So while the gas density law is law. what the fueling code doesn't take into effect is how the temperature of say the block of even the fuel relate to the air density.
As far as driving, if I need different fueling requirements base on temp, my EGO takes care of it and in boost my AFRs are very consistent and flat regardless of the ambient temp...so I dunno what to say.
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06-01-2012, 09:56 AM
#74
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yeha pretty much. if I was road racing it, I'd wanna test the effects more...but just doing boosted pulls on the hwy or something, I have no issues. I've barely touched the tune on this thing in over a year and the thing I've tuned were random odds and ends, like new idle code and the new accel-pump and stuff.
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06-01-2012, 10:54 AM
#77
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unsure, can you confirm the leaness is actually the gammae going below 100%?
i dont ever remember having this issue on MSI I always had it decay starting at 2500 and finishing around 5000 IIRC.
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06-01-2012, 05:08 PM
#79
yeha pretty much. if I was road racing it, I'd wanna test the effects more...but just doing boosted pulls on the hwy or something, I have no issues. I've barely touched the tune on this thing in over a year and the thing I've tuned were random odds and ends, like new idle code and the new accel-pump and stuff.
There is an easy ini change that can be made to allow 1% scaling which would Pretty much turn it off.
G
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